1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
5 <book id="drmDevelopersGuide">
7 <title>Linux DRM Developer's Guide</title>
11 <firstname>Jesse</firstname>
12 <surname>Barnes</surname>
13 <contrib>Initial version</contrib>
15 <orgname>Intel Corporation</orgname>
17 <email>jesse.barnes@intel.com</email>
22 <firstname>Laurent</firstname>
23 <surname>Pinchart</surname>
24 <contrib>Driver internals</contrib>
26 <orgname>Ideas on board SPRL</orgname>
28 <email>laurent.pinchart@ideasonboard.com</email>
33 <firstname>Daniel</firstname>
34 <surname>Vetter</surname>
35 <contrib>Contributions all over the place</contrib>
37 <orgname>Intel Corporation</orgname>
39 <email>daniel.vetter@ffwll.ch</email>
46 <year>2008-2009</year>
47 <year>2013-2014</year>
48 <holder>Intel Corporation</holder>
52 <holder>Laurent Pinchart</holder>
57 The contents of this file may be used under the terms of the GNU
58 General Public License version 2 (the "GPL") as distributed in
59 the kernel source COPYING file.
64 <!-- Put document revisions here, newest first. -->
66 <revnumber>1.0</revnumber>
67 <date>2012-07-13</date>
68 <authorinitials>LP</authorinitials>
69 <revremark>Added extensive documentation about driver internals.
78 <title>DRM Core</title>
81 This first part of the DRM Developer's Guide documents core DRM code,
82 helper libraries for writing drivers and generic userspace interfaces
83 exposed by DRM drivers.
87 <chapter id="drmIntroduction">
88 <title>Introduction</title>
90 The Linux DRM layer contains code intended to support the needs
91 of complex graphics devices, usually containing programmable
92 pipelines well suited to 3D graphics acceleration. Graphics
93 drivers in the kernel may make use of DRM functions to make
94 tasks like memory management, interrupt handling and DMA easier,
95 and provide a uniform interface to applications.
98 A note on versions: this guide covers features found in the DRM
99 tree, including the TTM memory manager, output configuration and
100 mode setting, and the new vblank internals, in addition to all
101 the regular features found in current kernels.
104 [Insert diagram of typical DRM stack here]
110 <chapter id="drmInternals">
111 <title>DRM Internals</title>
113 This chapter documents DRM internals relevant to driver authors
114 and developers working to add support for the latest features to
118 First, we go over some typical driver initialization
119 requirements, like setting up command buffers, creating an
120 initial output configuration, and initializing core services.
121 Subsequent sections cover core internals in more detail,
122 providing implementation notes and examples.
125 The DRM layer provides several services to graphics drivers,
126 many of them driven by the application interfaces it provides
127 through libdrm, the library that wraps most of the DRM ioctls.
128 These include vblank event handling, memory
129 management, output management, framebuffer management, command
130 submission & fencing, suspend/resume support, and DMA
134 <!-- Internals: driver init -->
137 <title>Driver Initialization</title>
139 At the core of every DRM driver is a <structname>drm_driver</structname>
140 structure. Drivers typically statically initialize a drm_driver structure,
141 and then pass it to one of the <function>drm_*_init()</function> functions
142 to register it with the DRM subsystem.
145 Newer drivers that no longer require a <structname>drm_bus</structname>
146 structure can alternatively use the low-level device initialization and
147 registration functions such as <function>drm_dev_alloc()</function> and
148 <function>drm_dev_register()</function> directly.
151 The <structname>drm_driver</structname> structure contains static
152 information that describes the driver and features it supports, and
153 pointers to methods that the DRM core will call to implement the DRM API.
154 We will first go through the <structname>drm_driver</structname> static
155 information fields, and will then describe individual operations in
156 details as they get used in later sections.
159 <title>Driver Information</title>
161 <title>Driver Features</title>
163 Drivers inform the DRM core about their requirements and supported
164 features by setting appropriate flags in the
165 <structfield>driver_features</structfield> field. Since those flags
166 influence the DRM core behaviour since registration time, most of them
167 must be set to registering the <structname>drm_driver</structname>
170 <synopsis>u32 driver_features;</synopsis>
172 <title>Driver Feature Flags</title>
174 <term>DRIVER_USE_AGP</term>
176 Driver uses AGP interface, the DRM core will manage AGP resources.
180 <term>DRIVER_REQUIRE_AGP</term>
182 Driver needs AGP interface to function. AGP initialization failure
183 will become a fatal error.
187 <term>DRIVER_PCI_DMA</term>
189 Driver is capable of PCI DMA, mapping of PCI DMA buffers to
190 userspace will be enabled. Deprecated.
194 <term>DRIVER_SG</term>
196 Driver can perform scatter/gather DMA, allocation and mapping of
197 scatter/gather buffers will be enabled. Deprecated.
201 <term>DRIVER_HAVE_DMA</term>
203 Driver supports DMA, the userspace DMA API will be supported.
208 <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
210 DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
211 managed by the DRM Core. The core will support simple IRQ handler
212 installation when the flag is set. The installation process is
213 described in <xref linkend="drm-irq-registration"/>.</para>
214 <para>DRIVER_IRQ_SHARED indicates whether the device & handler
215 support shared IRQs (note that this is required of PCI drivers).
219 <term>DRIVER_GEM</term>
221 Driver use the GEM memory manager.
225 <term>DRIVER_MODESET</term>
227 Driver supports mode setting interfaces (KMS).
231 <term>DRIVER_PRIME</term>
233 Driver implements DRM PRIME buffer sharing.
237 <term>DRIVER_RENDER</term>
239 Driver supports dedicated render nodes.
245 <title>Major, Minor and Patchlevel</title>
248 int patchlevel;</synopsis>
250 The DRM core identifies driver versions by a major, minor and patch
251 level triplet. The information is printed to the kernel log at
252 initialization time and passed to userspace through the
253 DRM_IOCTL_VERSION ioctl.
256 The major and minor numbers are also used to verify the requested driver
257 API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
258 between minor versions, applications can call DRM_IOCTL_SET_VERSION to
259 select a specific version of the API. If the requested major isn't equal
260 to the driver major, or the requested minor is larger than the driver
261 minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
262 the driver's set_version() method will be called with the requested
267 <title>Name, Description and Date</title>
268 <synopsis>char *name;
270 char *date;</synopsis>
272 The driver name is printed to the kernel log at initialization time,
273 used for IRQ registration and passed to userspace through
277 The driver description is a purely informative string passed to
278 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
282 The driver date, formatted as YYYYMMDD, is meant to identify the date of
283 the latest modification to the driver. However, as most drivers fail to
284 update it, its value is mostly useless. The DRM core prints it to the
285 kernel log at initialization time and passes it to userspace through the
286 DRM_IOCTL_VERSION ioctl.
291 <title>Device Registration</title>
293 A number of functions are provided to help with device registration.
294 The functions deal with PCI, USB and platform devices, respectively.
296 !Edrivers/gpu/drm/drm_pci.c
297 !Edrivers/gpu/drm/drm_usb.c
298 !Edrivers/gpu/drm/drm_platform.c
300 New drivers that no longer rely on the services provided by the
301 <structname>drm_bus</structname> structure can call the low-level
302 device registration functions directly. The
303 <function>drm_dev_alloc()</function> function can be used to allocate
304 and initialize a new <structname>drm_device</structname> structure.
305 Drivers will typically want to perform some additional setup on this
306 structure, such as allocating driver-specific data and storing a
307 pointer to it in the DRM device's <structfield>dev_private</structfield>
308 field. Drivers should also set the device's unique name using the
309 <function>drm_dev_set_unique()</function> function. After it has been
310 set up a device can be registered with the DRM subsystem by calling
311 <function>drm_dev_register()</function>. This will cause the device to
312 be exposed to userspace and will call the driver's
313 <structfield>.load()</structfield> implementation. When a device is
314 removed, the DRM device can safely be unregistered and freed by calling
315 <function>drm_dev_unregister()</function> followed by a call to
316 <function>drm_dev_unref()</function>.
318 !Edrivers/gpu/drm/drm_drv.c
321 <title>Driver Load</title>
323 The <methodname>load</methodname> method is the driver and device
324 initialization entry point. The method is responsible for allocating and
325 initializing driver private data, performing resource allocation and
326 mapping (e.g. acquiring
327 clocks, mapping registers or allocating command buffers), initializing
328 the memory manager (<xref linkend="drm-memory-management"/>), installing
329 the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
330 vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
331 setting (<xref linkend="drm-mode-setting"/>) and initial output
332 configuration (<xref linkend="drm-kms-init"/>).
335 If compatibility is a concern (e.g. with drivers converted over from
336 User Mode Setting to Kernel Mode Setting), care must be taken to prevent
337 device initialization and control that is incompatible with currently
338 active userspace drivers. For instance, if user level mode setting
339 drivers are in use, it would be problematic to perform output discovery
340 & configuration at load time. Likewise, if user-level drivers
341 unaware of memory management are in use, memory management and command
342 buffer setup may need to be omitted. These requirements are
343 driver-specific, and care needs to be taken to keep both old and new
344 applications and libraries working.
346 <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
348 The method takes two arguments, a pointer to the newly created
349 <structname>drm_device</structname> and flags. The flags are used to
350 pass the <structfield>driver_data</structfield> field of the device id
351 corresponding to the device passed to <function>drm_*_init()</function>.
352 Only PCI devices currently use this, USB and platform DRM drivers have
353 their <methodname>load</methodname> method called with flags to 0.
356 <title>Driver Private Data</title>
358 The driver private hangs off the main
359 <structname>drm_device</structname> structure and can be used for
360 tracking various device-specific bits of information, like register
361 offsets, command buffer status, register state for suspend/resume, etc.
362 At load time, a driver may simply allocate one and set
363 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
364 appropriately; it should be freed and
365 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
366 set to NULL when the driver is unloaded.
369 <sect3 id="drm-irq-registration">
370 <title>IRQ Registration</title>
372 The DRM core tries to facilitate IRQ handler registration and
373 unregistration by providing <function>drm_irq_install</function> and
374 <function>drm_irq_uninstall</function> functions. Those functions only
375 support a single interrupt per device, devices that use more than one
376 IRQs need to be handled manually.
379 <title>Managed IRQ Registration</title>
381 <function>drm_irq_install</function> starts by calling the
382 <methodname>irq_preinstall</methodname> driver operation. The operation
383 is optional and must make sure that the interrupt will not get fired by
384 clearing all pending interrupt flags or disabling the interrupt.
387 The passed-in IRQ will then be requested by a call to
388 <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
389 feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
393 The IRQ handler function must be provided as the mandatory irq_handler
394 driver operation. It will get passed directly to
395 <function>request_irq</function> and thus has the same prototype as all
396 IRQ handlers. It will get called with a pointer to the DRM device as the
400 Finally the function calls the optional
401 <methodname>irq_postinstall</methodname> driver operation. The operation
402 usually enables interrupts (excluding the vblank interrupt, which is
403 enabled separately), but drivers may choose to enable/disable interrupts
407 <function>drm_irq_uninstall</function> is similarly used to uninstall an
408 IRQ handler. It starts by waking up all processes waiting on a vblank
409 interrupt to make sure they don't hang, and then calls the optional
410 <methodname>irq_uninstall</methodname> driver operation. The operation
411 must disable all hardware interrupts. Finally the function frees the IRQ
412 by calling <function>free_irq</function>.
416 <title>Manual IRQ Registration</title>
418 Drivers that require multiple interrupt handlers can't use the managed
419 IRQ registration functions. In that case IRQs must be registered and
420 unregistered manually (usually with the <function>request_irq</function>
421 and <function>free_irq</function> functions, or their devm_* equivalent).
424 When manually registering IRQs, drivers must not set the DRIVER_HAVE_IRQ
425 driver feature flag, and must not provide the
426 <methodname>irq_handler</methodname> driver operation. They must set the
427 <structname>drm_device</structname> <structfield>irq_enabled</structfield>
428 field to 1 upon registration of the IRQs, and clear it to 0 after
429 unregistering the IRQs.
434 <title>Memory Manager Initialization</title>
436 Every DRM driver requires a memory manager which must be initialized at
437 load time. DRM currently contains two memory managers, the Translation
438 Table Manager (TTM) and the Graphics Execution Manager (GEM).
439 This document describes the use of the GEM memory manager only. See
440 <xref linkend="drm-memory-management"/> for details.
444 <title>Miscellaneous Device Configuration</title>
446 Another task that may be necessary for PCI devices during configuration
447 is mapping the video BIOS. On many devices, the VBIOS describes device
448 configuration, LCD panel timings (if any), and contains flags indicating
449 device state. Mapping the BIOS can be done using the pci_map_rom() call,
450 a convenience function that takes care of mapping the actual ROM,
451 whether it has been shadowed into memory (typically at address 0xc0000)
452 or exists on the PCI device in the ROM BAR. Note that after the ROM has
453 been mapped and any necessary information has been extracted, it should
454 be unmapped; on many devices, the ROM address decoder is shared with
455 other BARs, so leaving it mapped could cause undesired behaviour like
456 hangs or memory corruption.
457 <!--!Fdrivers/pci/rom.c pci_map_rom-->
463 <!-- Internals: memory management -->
465 <sect1 id="drm-memory-management">
466 <title>Memory management</title>
468 Modern Linux systems require large amount of graphics memory to store
469 frame buffers, textures, vertices and other graphics-related data. Given
470 the very dynamic nature of many of that data, managing graphics memory
471 efficiently is thus crucial for the graphics stack and plays a central
472 role in the DRM infrastructure.
475 The DRM core includes two memory managers, namely Translation Table Maps
476 (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
477 manager to be developed and tried to be a one-size-fits-them all
478 solution. It provides a single userspace API to accommodate the need of
479 all hardware, supporting both Unified Memory Architecture (UMA) devices
480 and devices with dedicated video RAM (i.e. most discrete video cards).
481 This resulted in a large, complex piece of code that turned out to be
482 hard to use for driver development.
485 GEM started as an Intel-sponsored project in reaction to TTM's
486 complexity. Its design philosophy is completely different: instead of
487 providing a solution to every graphics memory-related problems, GEM
488 identified common code between drivers and created a support library to
489 share it. GEM has simpler initialization and execution requirements than
490 TTM, but has no video RAM management capabilities and is thus limited to
494 <title>The Translation Table Manager (TTM)</title>
496 TTM design background and information belongs here.
499 <title>TTM initialization</title>
500 <warning><para>This section is outdated.</para></warning>
502 Drivers wishing to support TTM must fill out a drm_bo_driver
503 structure. The structure contains several fields with function
504 pointers for initializing the TTM, allocating and freeing memory,
505 waiting for command completion and fence synchronization, and memory
506 migration. See the radeon_ttm.c file for an example of usage.
509 The ttm_global_reference structure is made up of several fields:
512 struct ttm_global_reference {
513 enum ttm_global_types global_type;
516 int (*init) (struct ttm_global_reference *);
517 void (*release) (struct ttm_global_reference *);
521 There should be one global reference structure for your memory
522 manager as a whole, and there will be others for each object
523 created by the memory manager at runtime. Your global TTM should
524 have a type of TTM_GLOBAL_TTM_MEM. The size field for the global
525 object should be sizeof(struct ttm_mem_global), and the init and
526 release hooks should point at your driver-specific init and
527 release routines, which probably eventually call
528 ttm_mem_global_init and ttm_mem_global_release, respectively.
531 Once your global TTM accounting structure is set up and initialized
532 by calling ttm_global_item_ref() on it,
533 you need to create a buffer object TTM to
534 provide a pool for buffer object allocation by clients and the
535 kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO,
536 and its size should be sizeof(struct ttm_bo_global). Again,
537 driver-specific init and release functions may be provided,
538 likely eventually calling ttm_bo_global_init() and
539 ttm_bo_global_release(), respectively. Also, like the previous
540 object, ttm_global_item_ref() is used to create an initial reference
541 count for the TTM, which will call your initialization function.
546 <title>The Graphics Execution Manager (GEM)</title>
548 The GEM design approach has resulted in a memory manager that doesn't
549 provide full coverage of all (or even all common) use cases in its
550 userspace or kernel API. GEM exposes a set of standard memory-related
551 operations to userspace and a set of helper functions to drivers, and let
552 drivers implement hardware-specific operations with their own private API.
555 The GEM userspace API is described in the
556 <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
557 Execution Manager</citetitle></ulink> article on LWN. While slightly
558 outdated, the document provides a good overview of the GEM API principles.
559 Buffer allocation and read and write operations, described as part of the
560 common GEM API, are currently implemented using driver-specific ioctls.
563 GEM is data-agnostic. It manages abstract buffer objects without knowing
564 what individual buffers contain. APIs that require knowledge of buffer
565 contents or purpose, such as buffer allocation or synchronization
566 primitives, are thus outside of the scope of GEM and must be implemented
567 using driver-specific ioctls.
570 On a fundamental level, GEM involves several operations:
572 <listitem>Memory allocation and freeing</listitem>
573 <listitem>Command execution</listitem>
574 <listitem>Aperture management at command execution time</listitem>
576 Buffer object allocation is relatively straightforward and largely
577 provided by Linux's shmem layer, which provides memory to back each
581 Device-specific operations, such as command execution, pinning, buffer
582 read & write, mapping, and domain ownership transfers are left to
583 driver-specific ioctls.
586 <title>GEM Initialization</title>
588 Drivers that use GEM must set the DRIVER_GEM bit in the struct
589 <structname>drm_driver</structname>
590 <structfield>driver_features</structfield> field. The DRM core will
591 then automatically initialize the GEM core before calling the
592 <methodname>load</methodname> operation. Behind the scene, this will
593 create a DRM Memory Manager object which provides an address space
594 pool for object allocation.
597 In a KMS configuration, drivers need to allocate and initialize a
598 command ring buffer following core GEM initialization if required by
599 the hardware. UMA devices usually have what is called a "stolen"
600 memory region, which provides space for the initial framebuffer and
601 large, contiguous memory regions required by the device. This space is
602 typically not managed by GEM, and must be initialized separately into
603 its own DRM MM object.
607 <title>GEM Objects Creation</title>
609 GEM splits creation of GEM objects and allocation of the memory that
610 backs them in two distinct operations.
613 GEM objects are represented by an instance of struct
614 <structname>drm_gem_object</structname>. Drivers usually need to extend
615 GEM objects with private information and thus create a driver-specific
616 GEM object structure type that embeds an instance of struct
617 <structname>drm_gem_object</structname>.
620 To create a GEM object, a driver allocates memory for an instance of its
621 specific GEM object type and initializes the embedded struct
622 <structname>drm_gem_object</structname> with a call to
623 <function>drm_gem_object_init</function>. The function takes a pointer to
624 the DRM device, a pointer to the GEM object and the buffer object size
628 GEM uses shmem to allocate anonymous pageable memory.
629 <function>drm_gem_object_init</function> will create an shmfs file of
630 the requested size and store it into the struct
631 <structname>drm_gem_object</structname> <structfield>filp</structfield>
632 field. The memory is used as either main storage for the object when the
633 graphics hardware uses system memory directly or as a backing store
637 Drivers are responsible for the actual physical pages allocation by
638 calling <function>shmem_read_mapping_page_gfp</function> for each page.
639 Note that they can decide to allocate pages when initializing the GEM
640 object, or to delay allocation until the memory is needed (for instance
641 when a page fault occurs as a result of a userspace memory access or
642 when the driver needs to start a DMA transfer involving the memory).
645 Anonymous pageable memory allocation is not always desired, for instance
646 when the hardware requires physically contiguous system memory as is
647 often the case in embedded devices. Drivers can create GEM objects with
648 no shmfs backing (called private GEM objects) by initializing them with
649 a call to <function>drm_gem_private_object_init</function> instead of
650 <function>drm_gem_object_init</function>. Storage for private GEM
651 objects must be managed by drivers.
654 Drivers that do not need to extend GEM objects with private information
655 can call the <function>drm_gem_object_alloc</function> function to
656 allocate and initialize a struct <structname>drm_gem_object</structname>
657 instance. The GEM core will call the optional driver
658 <methodname>gem_init_object</methodname> operation after initializing
659 the GEM object with <function>drm_gem_object_init</function>.
660 <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
663 No alloc-and-init function exists for private GEM objects.
667 <title>GEM Objects Lifetime</title>
669 All GEM objects are reference-counted by the GEM core. References can be
670 acquired and release by <function>calling drm_gem_object_reference</function>
671 and <function>drm_gem_object_unreference</function> respectively. The
672 caller must hold the <structname>drm_device</structname>
673 <structfield>struct_mutex</structfield> lock. As a convenience, GEM
674 provides the <function>drm_gem_object_reference_unlocked</function> and
675 <function>drm_gem_object_unreference_unlocked</function> functions that
676 can be called without holding the lock.
679 When the last reference to a GEM object is released the GEM core calls
680 the <structname>drm_driver</structname>
681 <methodname>gem_free_object</methodname> operation. That operation is
682 mandatory for GEM-enabled drivers and must free the GEM object and all
683 associated resources.
686 <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
687 Drivers are responsible for freeing all GEM object resources, including
688 the resources created by the GEM core. If an mmap offset has been
689 created for the object (in which case
690 <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
691 is not NULL) it must be freed by a call to
692 <function>drm_gem_free_mmap_offset</function>. The shmfs backing store
693 must be released by calling <function>drm_gem_object_release</function>
694 (that function can safely be called if no shmfs backing store has been
699 <title>GEM Objects Naming</title>
701 Communication between userspace and the kernel refers to GEM objects
702 using local handles, global names or, more recently, file descriptors.
703 All of those are 32-bit integer values; the usual Linux kernel limits
704 apply to the file descriptors.
707 GEM handles are local to a DRM file. Applications get a handle to a GEM
708 object through a driver-specific ioctl, and can use that handle to refer
709 to the GEM object in other standard or driver-specific ioctls. Closing a
710 DRM file handle frees all its GEM handles and dereferences the
711 associated GEM objects.
714 To create a handle for a GEM object drivers call
715 <function>drm_gem_handle_create</function>. The function takes a pointer
716 to the DRM file and the GEM object and returns a locally unique handle.
717 When the handle is no longer needed drivers delete it with a call to
718 <function>drm_gem_handle_delete</function>. Finally the GEM object
719 associated with a handle can be retrieved by a call to
720 <function>drm_gem_object_lookup</function>.
723 Handles don't take ownership of GEM objects, they only take a reference
724 to the object that will be dropped when the handle is destroyed. To
725 avoid leaking GEM objects, drivers must make sure they drop the
726 reference(s) they own (such as the initial reference taken at object
727 creation time) as appropriate, without any special consideration for the
728 handle. For example, in the particular case of combined GEM object and
729 handle creation in the implementation of the
730 <methodname>dumb_create</methodname> operation, drivers must drop the
731 initial reference to the GEM object before returning the handle.
734 GEM names are similar in purpose to handles but are not local to DRM
735 files. They can be passed between processes to reference a GEM object
736 globally. Names can't be used directly to refer to objects in the DRM
737 API, applications must convert handles to names and names to handles
738 using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
739 respectively. The conversion is handled by the DRM core without any
740 driver-specific support.
743 GEM also supports buffer sharing with dma-buf file descriptors through
744 PRIME. GEM-based drivers must use the provided helpers functions to
745 implement the exporting and importing correctly. See <xref linkend="drm-prime-support" />.
746 Since sharing file descriptors is inherently more secure than the
747 easily guessable and global GEM names it is the preferred buffer
748 sharing mechanism. Sharing buffers through GEM names is only supported
749 for legacy userspace. Furthermore PRIME also allows cross-device
750 buffer sharing since it is based on dma-bufs.
753 <sect3 id="drm-gem-objects-mapping">
754 <title>GEM Objects Mapping</title>
756 Because mapping operations are fairly heavyweight GEM favours
757 read/write-like access to buffers, implemented through driver-specific
758 ioctls, over mapping buffers to userspace. However, when random access
759 to the buffer is needed (to perform software rendering for instance),
760 direct access to the object can be more efficient.
763 The mmap system call can't be used directly to map GEM objects, as they
764 don't have their own file handle. Two alternative methods currently
765 co-exist to map GEM objects to userspace. The first method uses a
766 driver-specific ioctl to perform the mapping operation, calling
767 <function>do_mmap</function> under the hood. This is often considered
768 dubious, seems to be discouraged for new GEM-enabled drivers, and will
769 thus not be described here.
772 The second method uses the mmap system call on the DRM file handle.
773 <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
774 off_t offset);</synopsis>
775 DRM identifies the GEM object to be mapped by a fake offset passed
776 through the mmap offset argument. Prior to being mapped, a GEM object
777 must thus be associated with a fake offset. To do so, drivers must call
778 <function>drm_gem_create_mmap_offset</function> on the object. The
779 function allocates a fake offset range from a pool and stores the
780 offset divided by PAGE_SIZE in
781 <literal>obj->map_list.hash.key</literal>. Care must be taken not to
782 call <function>drm_gem_create_mmap_offset</function> if a fake offset
783 has already been allocated for the object. This can be tested by
784 <literal>obj->map_list.map</literal> being non-NULL.
787 Once allocated, the fake offset value
788 (<literal>obj->map_list.hash.key << PAGE_SHIFT</literal>)
789 must be passed to the application in a driver-specific way and can then
790 be used as the mmap offset argument.
793 The GEM core provides a helper method <function>drm_gem_mmap</function>
794 to handle object mapping. The method can be set directly as the mmap
795 file operation handler. It will look up the GEM object based on the
796 offset value and set the VMA operations to the
797 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
798 field. Note that <function>drm_gem_mmap</function> doesn't map memory to
799 userspace, but relies on the driver-provided fault handler to map pages
803 To use <function>drm_gem_mmap</function>, drivers must fill the struct
804 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
805 field with a pointer to VM operations.
808 <synopsis>struct vm_operations_struct *gem_vm_ops
810 struct vm_operations_struct {
811 void (*open)(struct vm_area_struct * area);
812 void (*close)(struct vm_area_struct * area);
813 int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
817 The <methodname>open</methodname> and <methodname>close</methodname>
818 operations must update the GEM object reference count. Drivers can use
819 the <function>drm_gem_vm_open</function> and
820 <function>drm_gem_vm_close</function> helper functions directly as open
824 The fault operation handler is responsible for mapping individual pages
825 to userspace when a page fault occurs. Depending on the memory
826 allocation scheme, drivers can allocate pages at fault time, or can
827 decide to allocate memory for the GEM object at the time the object is
831 Drivers that want to map the GEM object upfront instead of handling page
832 faults can implement their own mmap file operation handler.
836 <title>Memory Coherency</title>
838 When mapped to the device or used in a command buffer, backing pages
839 for an object are flushed to memory and marked write combined so as to
840 be coherent with the GPU. Likewise, if the CPU accesses an object
841 after the GPU has finished rendering to the object, then the object
842 must be made coherent with the CPU's view of memory, usually involving
843 GPU cache flushing of various kinds. This core CPU<->GPU
844 coherency management is provided by a device-specific ioctl, which
845 evaluates an object's current domain and performs any necessary
846 flushing or synchronization to put the object into the desired
847 coherency domain (note that the object may be busy, i.e. an active
848 render target; in that case, setting the domain blocks the client and
849 waits for rendering to complete before performing any necessary
850 flushing operations).
854 <title>Command Execution</title>
856 Perhaps the most important GEM function for GPU devices is providing a
857 command execution interface to clients. Client programs construct
858 command buffers containing references to previously allocated memory
859 objects, and then submit them to GEM. At that point, GEM takes care to
860 bind all the objects into the GTT, execute the buffer, and provide
861 necessary synchronization between clients accessing the same buffers.
862 This often involves evicting some objects from the GTT and re-binding
863 others (a fairly expensive operation), and providing relocation
864 support which hides fixed GTT offsets from clients. Clients must take
865 care not to submit command buffers that reference more objects than
866 can fit in the GTT; otherwise, GEM will reject them and no rendering
867 will occur. Similarly, if several objects in the buffer require fence
868 registers to be allocated for correct rendering (e.g. 2D blits on
869 pre-965 chips), care must be taken not to require more fence registers
870 than are available to the client. Such resource management should be
871 abstracted from the client in libdrm.
875 <title>GEM Function Reference</title>
876 !Edrivers/gpu/drm/drm_gem.c
880 <title>VMA Offset Manager</title>
881 !Pdrivers/gpu/drm/drm_vma_manager.c vma offset manager
882 !Edrivers/gpu/drm/drm_vma_manager.c
883 !Iinclude/drm/drm_vma_manager.h
885 <sect2 id="drm-prime-support">
886 <title>PRIME Buffer Sharing</title>
888 PRIME is the cross device buffer sharing framework in drm, originally
889 created for the OPTIMUS range of multi-gpu platforms. To userspace
890 PRIME buffers are dma-buf based file descriptors.
893 <title>Overview and Driver Interface</title>
895 Similar to GEM global names, PRIME file descriptors are
896 also used to share buffer objects across processes. They offer
897 additional security: as file descriptors must be explicitly sent over
898 UNIX domain sockets to be shared between applications, they can't be
899 guessed like the globally unique GEM names.
902 Drivers that support the PRIME
903 API must set the DRIVER_PRIME bit in the struct
904 <structname>drm_driver</structname>
905 <structfield>driver_features</structfield> field, and implement the
906 <methodname>prime_handle_to_fd</methodname> and
907 <methodname>prime_fd_to_handle</methodname> operations.
910 <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
911 struct drm_file *file_priv, uint32_t handle,
912 uint32_t flags, int *prime_fd);
913 int (*prime_fd_to_handle)(struct drm_device *dev,
914 struct drm_file *file_priv, int prime_fd,
915 uint32_t *handle);</synopsis>
916 Those two operations convert a handle to a PRIME file descriptor and
917 vice versa. Drivers must use the kernel dma-buf buffer sharing framework
918 to manage the PRIME file descriptors. Similar to the mode setting
919 API PRIME is agnostic to the underlying buffer object manager, as
920 long as handles are 32bit unsigned integers.
923 While non-GEM drivers must implement the operations themselves, GEM
924 drivers must use the <function>drm_gem_prime_handle_to_fd</function>
925 and <function>drm_gem_prime_fd_to_handle</function> helper functions.
926 Those helpers rely on the driver
927 <methodname>gem_prime_export</methodname> and
928 <methodname>gem_prime_import</methodname> operations to create a dma-buf
929 instance from a GEM object (dma-buf exporter role) and to create a GEM
930 object from a dma-buf instance (dma-buf importer role).
933 <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
934 struct drm_gem_object *obj,
936 struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
937 struct dma_buf *dma_buf);</synopsis>
938 These two operations are mandatory for GEM drivers that support
943 <title>PRIME Helper Functions</title>
944 !Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
948 <title>PRIME Function References</title>
949 !Edrivers/gpu/drm/drm_prime.c
952 <title>DRM MM Range Allocator</title>
954 <title>Overview</title>
955 !Pdrivers/gpu/drm/drm_mm.c Overview
958 <title>LRU Scan/Eviction Support</title>
959 !Pdrivers/gpu/drm/drm_mm.c lru scan roaster
963 <title>DRM MM Range Allocator Function References</title>
964 !Edrivers/gpu/drm/drm_mm.c
965 !Iinclude/drm/drm_mm.h
969 <!-- Internals: mode setting -->
971 <sect1 id="drm-mode-setting">
972 <title>Mode Setting</title>
974 Drivers must initialize the mode setting core by calling
975 <function>drm_mode_config_init</function> on the DRM device. The function
976 initializes the <structname>drm_device</structname>
977 <structfield>mode_config</structfield> field and never fails. Once done,
978 mode configuration must be setup by initializing the following fields.
982 <synopsis>int min_width, min_height;
983 int max_width, max_height;</synopsis>
985 Minimum and maximum width and height of the frame buffers in pixel
990 <synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
991 <para>Mode setting functions.</para>
995 <title>Display Modes Function Reference</title>
996 !Iinclude/drm/drm_modes.h
997 !Edrivers/gpu/drm/drm_modes.c
1000 <title>Frame Buffer Creation</title>
1001 <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
1002 struct drm_file *file_priv,
1003 struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
1005 Frame buffers are abstract memory objects that provide a source of
1006 pixels to scanout to a CRTC. Applications explicitly request the
1007 creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
1008 receive an opaque handle that can be passed to the KMS CRTC control,
1009 plane configuration and page flip functions.
1012 Frame buffers rely on the underneath memory manager for low-level memory
1013 operations. When creating a frame buffer applications pass a memory
1014 handle (or a list of memory handles for multi-planar formats) through
1015 the <parameter>drm_mode_fb_cmd2</parameter> argument. For drivers using
1016 GEM as their userspace buffer management interface this would be a GEM
1017 handle. Drivers are however free to use their own backing storage object
1018 handles, e.g. vmwgfx directly exposes special TTM handles to userspace
1019 and so expects TTM handles in the create ioctl and not GEM handles.
1022 Drivers must first validate the requested frame buffer parameters passed
1023 through the mode_cmd argument. In particular this is where invalid
1024 sizes, pixel formats or pitches can be caught.
1027 If the parameters are deemed valid, drivers then create, initialize and
1028 return an instance of struct <structname>drm_framebuffer</structname>.
1029 If desired the instance can be embedded in a larger driver-specific
1030 structure. Drivers must fill its <structfield>width</structfield>,
1031 <structfield>height</structfield>, <structfield>pitches</structfield>,
1032 <structfield>offsets</structfield>, <structfield>depth</structfield>,
1033 <structfield>bits_per_pixel</structfield> and
1034 <structfield>pixel_format</structfield> fields from the values passed
1035 through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
1036 should call the <function>drm_helper_mode_fill_fb_struct</function>
1037 helper function to do so.
1041 The initialization of the new framebuffer instance is finalized with a
1042 call to <function>drm_framebuffer_init</function> which takes a pointer
1043 to DRM frame buffer operations (struct
1044 <structname>drm_framebuffer_funcs</structname>). Note that this function
1045 publishes the framebuffer and so from this point on it can be accessed
1046 concurrently from other threads. Hence it must be the last step in the
1047 driver's framebuffer initialization sequence. Frame buffer operations
1051 <synopsis>int (*create_handle)(struct drm_framebuffer *fb,
1052 struct drm_file *file_priv, unsigned int *handle);</synopsis>
1054 Create a handle to the frame buffer underlying memory object. If
1055 the frame buffer uses a multi-plane format, the handle will
1056 reference the memory object associated with the first plane.
1059 Drivers call <function>drm_gem_handle_create</function> to create
1064 <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
1066 Destroy the frame buffer object and frees all associated
1067 resources. Drivers must call
1068 <function>drm_framebuffer_cleanup</function> to free resources
1069 allocated by the DRM core for the frame buffer object, and must
1070 make sure to unreference all memory objects associated with the
1071 frame buffer. Handles created by the
1072 <methodname>create_handle</methodname> operation are released by
1077 <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
1078 struct drm_file *file_priv, unsigned flags, unsigned color,
1079 struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
1081 This optional operation notifies the driver that a region of the
1082 frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
1089 The lifetime of a drm framebuffer is controlled with a reference count,
1090 drivers can grab additional references with
1091 <function>drm_framebuffer_reference</function>and drop them
1092 again with <function>drm_framebuffer_unreference</function>. For
1093 driver-private framebuffers for which the last reference is never
1094 dropped (e.g. for the fbdev framebuffer when the struct
1095 <structname>drm_framebuffer</structname> is embedded into the fbdev
1096 helper struct) drivers can manually clean up a framebuffer at module
1098 <function>drm_framebuffer_unregister_private</function>.
1102 <title>Dumb Buffer Objects</title>
1104 The KMS API doesn't standardize backing storage object creation and
1105 leaves it to driver-specific ioctls. Furthermore actually creating a
1106 buffer object even for GEM-based drivers is done through a
1107 driver-specific ioctl - GEM only has a common userspace interface for
1108 sharing and destroying objects. While not an issue for full-fledged
1109 graphics stacks that include device-specific userspace components (in
1110 libdrm for instance), this limit makes DRM-based early boot graphics
1111 unnecessarily complex.
1114 Dumb objects partly alleviate the problem by providing a standard
1115 API to create dumb buffers suitable for scanout, which can then be used
1116 to create KMS frame buffers.
1119 To support dumb objects drivers must implement the
1120 <methodname>dumb_create</methodname>,
1121 <methodname>dumb_destroy</methodname> and
1122 <methodname>dumb_map_offset</methodname> operations.
1126 <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
1127 struct drm_mode_create_dumb *args);</synopsis>
1129 The <methodname>dumb_create</methodname> operation creates a driver
1130 object (GEM or TTM handle) suitable for scanout based on the
1131 width, height and depth from the struct
1132 <structname>drm_mode_create_dumb</structname> argument. It fills the
1133 argument's <structfield>handle</structfield>,
1134 <structfield>pitch</structfield> and <structfield>size</structfield>
1135 fields with a handle for the newly created object and its line
1136 pitch and size in bytes.
1140 <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
1141 uint32_t handle);</synopsis>
1143 The <methodname>dumb_destroy</methodname> operation destroys a dumb
1144 object created by <methodname>dumb_create</methodname>.
1148 <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
1149 uint32_t handle, uint64_t *offset);</synopsis>
1151 The <methodname>dumb_map_offset</methodname> operation associates an
1152 mmap fake offset with the object given by the handle and returns
1153 it. Drivers must use the
1154 <function>drm_gem_create_mmap_offset</function> function to
1155 associate the fake offset as described in
1156 <xref linkend="drm-gem-objects-mapping"/>.
1161 Note that dumb objects may not be used for gpu acceleration, as has been
1162 attempted on some ARM embedded platforms. Such drivers really must have
1163 a hardware-specific ioctl to allocate suitable buffer objects.
1167 <title>Output Polling</title>
1168 <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
1170 This operation notifies the driver that the status of one or more
1171 connectors has changed. Drivers that use the fb helper can just call the
1172 <function>drm_fb_helper_hotplug_event</function> function to handle this
1177 <title>Locking</title>
1179 Beside some lookup structures with their own locking (which is hidden
1180 behind the interface functions) most of the modeset state is protected
1181 by the <code>dev-<mode_config.lock</code> mutex and additionally
1182 per-crtc locks to allow cursor updates, pageflips and similar operations
1183 to occur concurrently with background tasks like output detection.
1184 Operations which cross domains like a full modeset always grab all
1185 locks. Drivers there need to protect resources shared between crtcs with
1186 additional locking. They also need to be careful to always grab the
1187 relevant crtc locks if a modset functions touches crtc state, e.g. for
1188 load detection (which does only grab the <code>mode_config.lock</code>
1189 to allow concurrent screen updates on live crtcs).
1194 <!-- Internals: kms initialization and cleanup -->
1196 <sect1 id="drm-kms-init">
1197 <title>KMS Initialization and Cleanup</title>
1199 A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
1200 and connectors. KMS drivers must thus create and initialize all those
1201 objects at load time after initializing mode setting.
1204 <title>CRTCs (struct <structname>drm_crtc</structname>)</title>
1206 A CRTC is an abstraction representing a part of the chip that contains a
1207 pointer to a scanout buffer. Therefore, the number of CRTCs available
1208 determines how many independent scanout buffers can be active at any
1209 given time. The CRTC structure contains several fields to support this:
1210 a pointer to some video memory (abstracted as a frame buffer object), a
1211 display mode, and an (x, y) offset into the video memory to support
1212 panning or configurations where one piece of video memory spans multiple
1216 <title>CRTC Initialization</title>
1218 A KMS device must create and register at least one struct
1219 <structname>drm_crtc</structname> instance. The instance is allocated
1220 and zeroed by the driver, possibly as part of a larger structure, and
1221 registered with a call to <function>drm_crtc_init</function> with a
1222 pointer to CRTC functions.
1225 <sect3 id="drm-kms-crtcops">
1226 <title>CRTC Operations</title>
1228 <title>Set Configuration</title>
1229 <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
1231 Apply a new CRTC configuration to the device. The configuration
1232 specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
1233 the frame buffer, a display mode and an array of connectors to drive
1234 with the CRTC if possible.
1237 If the frame buffer specified in the configuration is NULL, the driver
1238 must detach all encoders connected to the CRTC and all connectors
1239 attached to those encoders and disable them.
1242 This operation is called with the mode config lock held.
1245 Note that the drm core has no notion of restoring the mode setting
1246 state after resume, since all resume handling is in the full
1247 responsibility of the driver. The common mode setting helper library
1248 though provides a helper which can be used for this:
1249 <function>drm_helper_resume_force_mode</function>.
1253 <title>Page Flipping</title>
1254 <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
1255 struct drm_pending_vblank_event *event);</synopsis>
1257 Schedule a page flip to the given frame buffer for the CRTC. This
1258 operation is called with the mode config mutex held.
1261 Page flipping is a synchronization mechanism that replaces the frame
1262 buffer being scanned out by the CRTC with a new frame buffer during
1263 vertical blanking, avoiding tearing. When an application requests a page
1264 flip the DRM core verifies that the new frame buffer is large enough to
1265 be scanned out by the CRTC in the currently configured mode and then
1266 calls the CRTC <methodname>page_flip</methodname> operation with a
1267 pointer to the new frame buffer.
1270 The <methodname>page_flip</methodname> operation schedules a page flip.
1271 Once any pending rendering targeting the new frame buffer has
1272 completed, the CRTC will be reprogrammed to display that frame buffer
1273 after the next vertical refresh. The operation must return immediately
1274 without waiting for rendering or page flip to complete and must block
1275 any new rendering to the frame buffer until the page flip completes.
1278 If a page flip can be successfully scheduled the driver must set the
1279 <code>drm_crtc-<fb</code> field to the new framebuffer pointed to
1280 by <code>fb</code>. This is important so that the reference counting
1281 on framebuffers stays balanced.
1284 If a page flip is already pending, the
1285 <methodname>page_flip</methodname> operation must return
1286 -<errorname>EBUSY</errorname>.
1289 To synchronize page flip to vertical blanking the driver will likely
1290 need to enable vertical blanking interrupts. It should call
1291 <function>drm_vblank_get</function> for that purpose, and call
1292 <function>drm_vblank_put</function> after the page flip completes.
1295 If the application has requested to be notified when page flip completes
1296 the <methodname>page_flip</methodname> operation will be called with a
1297 non-NULL <parameter>event</parameter> argument pointing to a
1298 <structname>drm_pending_vblank_event</structname> instance. Upon page
1299 flip completion the driver must call <methodname>drm_send_vblank_event</methodname>
1300 to fill in the event and send to wake up any waiting processes.
1301 This can be performed with
1302 <programlisting><![CDATA[
1303 spin_lock_irqsave(&dev->event_lock, flags);
1305 drm_send_vblank_event(dev, pipe, event);
1306 spin_unlock_irqrestore(&dev->event_lock, flags);
1307 ]]></programlisting>
1310 FIXME: Could drivers that don't need to wait for rendering to complete
1311 just add the event to <literal>dev->vblank_event_list</literal> and
1312 let the DRM core handle everything, as for "normal" vertical blanking
1316 While waiting for the page flip to complete, the
1317 <literal>event->base.link</literal> list head can be used freely by
1318 the driver to store the pending event in a driver-specific list.
1321 If the file handle is closed before the event is signaled, drivers must
1322 take care to destroy the event in their
1323 <methodname>preclose</methodname> operation (and, if needed, call
1324 <function>drm_vblank_put</function>).
1328 <title>Miscellaneous</title>
1331 <synopsis>void (*set_property)(struct drm_crtc *crtc,
1332 struct drm_property *property, uint64_t value);</synopsis>
1334 Set the value of the given CRTC property to
1335 <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1336 for more information about properties.
1340 <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
1341 uint32_t start, uint32_t size);</synopsis>
1343 Apply a gamma table to the device. The operation is optional.
1347 <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
1349 Destroy the CRTC when not needed anymore. See
1350 <xref linkend="drm-kms-init"/>.
1358 <title>Planes (struct <structname>drm_plane</structname>)</title>
1360 A plane represents an image source that can be blended with or overlayed
1361 on top of a CRTC during the scanout process. Planes are associated with
1362 a frame buffer to crop a portion of the image memory (source) and
1363 optionally scale it to a destination size. The result is then blended
1364 with or overlayed on top of a CRTC.
1367 The DRM core recognizes three types of planes:
1370 DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC. Primary
1371 planes are the planes operated upon by by CRTC modesetting and flipping
1372 operations described in <xref linkend="drm-kms-crtcops"/>.
1375 DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC. Cursor
1376 planes are the planes operated upon by the DRM_IOCTL_MODE_CURSOR and
1377 DRM_IOCTL_MODE_CURSOR2 ioctls.
1380 DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor planes.
1381 Some drivers refer to these types of planes as "sprites" internally.
1384 For compatibility with legacy userspace, only overlay planes are made
1385 available to userspace by default. Userspace clients may set the
1386 DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate that
1387 they wish to receive a universal plane list containing all plane types.
1390 <title>Plane Initialization</title>
1392 To create a plane, a KMS drivers allocates and
1393 zeroes an instances of struct <structname>drm_plane</structname>
1394 (possibly as part of a larger structure) and registers it with a call
1395 to <function>drm_universal_plane_init</function>. The function takes a bitmask
1396 of the CRTCs that can be associated with the plane, a pointer to the
1397 plane functions, a list of format supported formats, and the type of
1398 plane (primary, cursor, or overlay) being initialized.
1401 Cursor and overlay planes are optional. All drivers should provide
1402 one primary plane per CRTC (although this requirement may change in
1403 the future); drivers that do not wish to provide special handling for
1404 primary planes may make use of the helper functions described in
1405 <xref linkend="drm-kms-planehelpers"/> to create and register a
1406 primary plane with standard capabilities.
1410 <title>Plane Operations</title>
1413 <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
1414 struct drm_framebuffer *fb, int crtc_x, int crtc_y,
1415 unsigned int crtc_w, unsigned int crtc_h,
1416 uint32_t src_x, uint32_t src_y,
1417 uint32_t src_w, uint32_t src_h);</synopsis>
1419 Enable and configure the plane to use the given CRTC and frame buffer.
1422 The source rectangle in frame buffer memory coordinates is given by
1423 the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
1424 <parameter>src_w</parameter> and <parameter>src_h</parameter>
1425 parameters (as 16.16 fixed point values). Devices that don't support
1426 subpixel plane coordinates can ignore the fractional part.
1429 The destination rectangle in CRTC coordinates is given by the
1430 <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
1431 <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
1432 parameters (as integer values). Devices scale the source rectangle to
1433 the destination rectangle. If scaling is not supported, and the source
1434 rectangle size doesn't match the destination rectangle size, the
1435 driver must return a -<errorname>EINVAL</errorname> error.
1439 <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
1441 Disable the plane. The DRM core calls this method in response to a
1442 DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
1443 Disabled planes must not be processed by the CRTC.
1447 <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
1449 Destroy the plane when not needed anymore. See
1450 <xref linkend="drm-kms-init"/>.
1457 <title>Encoders (struct <structname>drm_encoder</structname>)</title>
1459 An encoder takes pixel data from a CRTC and converts it to a format
1460 suitable for any attached connectors. On some devices, it may be
1461 possible to have a CRTC send data to more than one encoder. In that
1462 case, both encoders would receive data from the same scanout buffer,
1463 resulting in a "cloned" display configuration across the connectors
1464 attached to each encoder.
1467 <title>Encoder Initialization</title>
1469 As for CRTCs, a KMS driver must create, initialize and register at
1470 least one struct <structname>drm_encoder</structname> instance. The
1471 instance is allocated and zeroed by the driver, possibly as part of a
1475 Drivers must initialize the struct <structname>drm_encoder</structname>
1476 <structfield>possible_crtcs</structfield> and
1477 <structfield>possible_clones</structfield> fields before registering the
1478 encoder. Both fields are bitmasks of respectively the CRTCs that the
1479 encoder can be connected to, and sibling encoders candidate for cloning.
1482 After being initialized, the encoder must be registered with a call to
1483 <function>drm_encoder_init</function>. The function takes a pointer to
1484 the encoder functions and an encoder type. Supported types are
1487 DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
1490 DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
1493 DRM_MODE_ENCODER_LVDS for display panels
1496 DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
1500 DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
1505 Encoders must be attached to a CRTC to be used. DRM drivers leave
1506 encoders unattached at initialization time. Applications (or the fbdev
1507 compatibility layer when implemented) are responsible for attaching the
1508 encoders they want to use to a CRTC.
1512 <title>Encoder Operations</title>
1515 <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
1517 Called to destroy the encoder when not needed anymore. See
1518 <xref linkend="drm-kms-init"/>.
1522 <synopsis>void (*set_property)(struct drm_plane *plane,
1523 struct drm_property *property, uint64_t value);</synopsis>
1525 Set the value of the given plane property to
1526 <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1527 for more information about properties.
1534 <title>Connectors (struct <structname>drm_connector</structname>)</title>
1536 A connector is the final destination for pixel data on a device, and
1537 usually connects directly to an external display device like a monitor
1538 or laptop panel. A connector can only be attached to one encoder at a
1539 time. The connector is also the structure where information about the
1540 attached display is kept, so it contains fields for display data, EDID
1541 data, DPMS & connection status, and information about modes
1542 supported on the attached displays.
1545 <title>Connector Initialization</title>
1547 Finally a KMS driver must create, initialize, register and attach at
1548 least one struct <structname>drm_connector</structname> instance. The
1549 instance is created as other KMS objects and initialized by setting the
1554 <term><structfield>interlace_allowed</structfield></term>
1556 Whether the connector can handle interlaced modes.
1560 <term><structfield>doublescan_allowed</structfield></term>
1562 Whether the connector can handle doublescan.
1566 <term><structfield>display_info
1567 </structfield></term>
1569 Display information is filled from EDID information when a display
1570 is detected. For non hot-pluggable displays such as flat panels in
1571 embedded systems, the driver should initialize the
1572 <structfield>display_info</structfield>.<structfield>width_mm</structfield>
1574 <structfield>display_info</structfield>.<structfield>height_mm</structfield>
1575 fields with the physical size of the display.
1579 <term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
1581 Connector polling mode, a combination of
1584 <term>DRM_CONNECTOR_POLL_HPD</term>
1586 The connector generates hotplug events and doesn't need to be
1587 periodically polled. The CONNECT and DISCONNECT flags must not
1588 be set together with the HPD flag.
1592 <term>DRM_CONNECTOR_POLL_CONNECT</term>
1594 Periodically poll the connector for connection.
1598 <term>DRM_CONNECTOR_POLL_DISCONNECT</term>
1600 Periodically poll the connector for disconnection.
1604 Set to 0 for connectors that don't support connection status
1610 The connector is then registered with a call to
1611 <function>drm_connector_init</function> with a pointer to the connector
1612 functions and a connector type, and exposed through sysfs with a call to
1613 <function>drm_connector_register</function>.
1616 Supported connector types are
1618 <listitem>DRM_MODE_CONNECTOR_VGA</listitem>
1619 <listitem>DRM_MODE_CONNECTOR_DVII</listitem>
1620 <listitem>DRM_MODE_CONNECTOR_DVID</listitem>
1621 <listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
1622 <listitem>DRM_MODE_CONNECTOR_Composite</listitem>
1623 <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
1624 <listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
1625 <listitem>DRM_MODE_CONNECTOR_Component</listitem>
1626 <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
1627 <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
1628 <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
1629 <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
1630 <listitem>DRM_MODE_CONNECTOR_TV</listitem>
1631 <listitem>DRM_MODE_CONNECTOR_eDP</listitem>
1632 <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
1636 Connectors must be attached to an encoder to be used. For devices that
1637 map connectors to encoders 1:1, the connector should be attached at
1638 initialization time with a call to
1639 <function>drm_mode_connector_attach_encoder</function>. The driver must
1640 also set the <structname>drm_connector</structname>
1641 <structfield>encoder</structfield> field to point to the attached
1645 Finally, drivers must initialize the connectors state change detection
1646 with a call to <function>drm_kms_helper_poll_init</function>. If at
1647 least one connector is pollable but can't generate hotplug interrupts
1648 (indicated by the DRM_CONNECTOR_POLL_CONNECT and
1649 DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
1650 automatically be queued to periodically poll for changes. Connectors
1651 that can generate hotplug interrupts must be marked with the
1652 DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
1653 call <function>drm_helper_hpd_irq_event</function>. The function will
1654 queue a delayed work to check the state of all connectors, but no
1655 periodic polling will be done.
1659 <title>Connector Operations</title>
1661 Unless otherwise state, all operations are mandatory.
1665 <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
1667 The DPMS operation sets the power state of a connector. The mode
1670 <listitem><para>DRM_MODE_DPMS_ON</para></listitem>
1671 <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
1672 <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
1673 <listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
1677 In all but DPMS_ON mode the encoder to which the connector is attached
1678 should put the display in low-power mode by driving its signals
1679 appropriately. If more than one connector is attached to the encoder
1680 care should be taken not to change the power state of other displays as
1681 a side effect. Low-power mode should be propagated to the encoders and
1682 CRTCs when all related connectors are put in low-power mode.
1686 <title>Modes</title>
1687 <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
1688 uint32_t max_height);</synopsis>
1690 Fill the mode list with all supported modes for the connector. If the
1691 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1692 arguments are non-zero, the implementation must ignore all modes wider
1693 than <parameter>max_width</parameter> or higher than
1694 <parameter>max_height</parameter>.
1697 The connector must also fill in this operation its
1698 <structfield>display_info</structfield>
1699 <structfield>width_mm</structfield> and
1700 <structfield>height_mm</structfield> fields with the connected display
1701 physical size in millimeters. The fields should be set to 0 if the value
1702 isn't known or is not applicable (for instance for projector devices).
1706 <title>Connection Status</title>
1708 The connection status is updated through polling or hotplug events when
1709 supported (see <xref linkend="drm-kms-connector-polled"/>). The status
1710 value is reported to userspace through ioctls and must not be used
1711 inside the driver, as it only gets initialized by a call to
1712 <function>drm_mode_getconnector</function> from userspace.
1714 <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
1715 bool force);</synopsis>
1717 Check to see if anything is attached to the connector. The
1718 <parameter>force</parameter> parameter is set to false whilst polling or
1719 to true when checking the connector due to user request.
1720 <parameter>force</parameter> can be used by the driver to avoid
1721 expensive, destructive operations during automated probing.
1724 Return connector_status_connected if something is connected to the
1725 connector, connector_status_disconnected if nothing is connected and
1726 connector_status_unknown if the connection state isn't known.
1729 Drivers should only return connector_status_connected if the connection
1730 status has really been probed as connected. Connectors that can't detect
1731 the connection status, or failed connection status probes, should return
1732 connector_status_unknown.
1736 <title>Miscellaneous</title>
1739 <synopsis>void (*set_property)(struct drm_connector *connector,
1740 struct drm_property *property, uint64_t value);</synopsis>
1742 Set the value of the given connector property to
1743 <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1744 for more information about properties.
1748 <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
1750 Destroy the connector when not needed anymore. See
1751 <xref linkend="drm-kms-init"/>.
1759 <title>Cleanup</title>
1761 The DRM core manages its objects' lifetime. When an object is not needed
1762 anymore the core calls its destroy function, which must clean up and
1763 free every resource allocated for the object. Every
1764 <function>drm_*_init</function> call must be matched with a
1765 corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
1766 (<function>drm_crtc_cleanup</function>), planes
1767 (<function>drm_plane_cleanup</function>), encoders
1768 (<function>drm_encoder_cleanup</function>) and connectors
1769 (<function>drm_connector_cleanup</function>). Furthermore, connectors
1770 that have been added to sysfs must be removed by a call to
1771 <function>drm_connector_unregister</function> before calling
1772 <function>drm_connector_cleanup</function>.
1775 Connectors state change detection must be cleanup up with a call to
1776 <function>drm_kms_helper_poll_fini</function>.
1780 <title>Output discovery and initialization example</title>
1781 <programlisting><![CDATA[
1782 void intel_crt_init(struct drm_device *dev)
1784 struct drm_connector *connector;
1785 struct intel_output *intel_output;
1787 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
1791 connector = &intel_output->base;
1792 drm_connector_init(dev, &intel_output->base,
1793 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
1795 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
1796 DRM_MODE_ENCODER_DAC);
1798 drm_mode_connector_attach_encoder(&intel_output->base,
1799 &intel_output->enc);
1801 /* Set up the DDC bus. */
1802 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
1803 if (!intel_output->ddc_bus) {
1804 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
1809 intel_output->type = INTEL_OUTPUT_ANALOG;
1810 connector->interlace_allowed = 0;
1811 connector->doublescan_allowed = 0;
1813 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
1814 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
1816 drm_connector_register(connector);
1817 }]]></programlisting>
1819 In the example above (taken from the i915 driver), a CRTC, connector and
1820 encoder combination is created. A device-specific i2c bus is also
1821 created for fetching EDID data and performing monitor detection. Once
1822 the process is complete, the new connector is registered with sysfs to
1823 make its properties available to applications.
1827 <title>KMS API Functions</title>
1828 !Edrivers/gpu/drm/drm_crtc.c
1831 <title>KMS Locking</title>
1832 !Pdrivers/gpu/drm/drm_modeset_lock.c kms locking
1833 !Iinclude/drm/drm_modeset_lock.h
1834 !Edrivers/gpu/drm/drm_modeset_lock.c
1838 <!-- Internals: kms helper functions -->
1841 <title>Mode Setting Helper Functions</title>
1843 The plane, CRTC, encoder and connector functions provided by the drivers
1844 implement the DRM API. They're called by the DRM core and ioctl handlers
1845 to handle device state changes and configuration request. As implementing
1846 those functions often requires logic not specific to drivers, mid-layer
1847 helper functions are available to avoid duplicating boilerplate code.
1850 The DRM core contains one mid-layer implementation. The mid-layer provides
1851 implementations of several plane, CRTC, encoder and connector functions
1852 (called from the top of the mid-layer) that pre-process requests and call
1853 lower-level functions provided by the driver (at the bottom of the
1854 mid-layer). For instance, the
1855 <function>drm_crtc_helper_set_config</function> function can be used to
1856 fill the struct <structname>drm_crtc_funcs</structname>
1857 <structfield>set_config</structfield> field. When called, it will split
1858 the <methodname>set_config</methodname> operation in smaller, simpler
1859 operations and call the driver to handle them.
1862 To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
1863 <function>drm_encoder_helper_add</function> and
1864 <function>drm_connector_helper_add</function> functions to install their
1865 mid-layer bottom operations handlers, and fill the
1866 <structname>drm_crtc_funcs</structname>,
1867 <structname>drm_encoder_funcs</structname> and
1868 <structname>drm_connector_funcs</structname> structures with pointers to
1869 the mid-layer top API functions. Installing the mid-layer bottom operation
1870 handlers is best done right after registering the corresponding KMS object.
1873 The mid-layer is not split between CRTC, encoder and connector operations.
1874 To use it, a driver must provide bottom functions for all of the three KMS
1878 <title>Helper Functions</title>
1881 <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
1883 The <function>drm_crtc_helper_set_config</function> helper function
1884 is a CRTC <methodname>set_config</methodname> implementation. It
1885 first tries to locate the best encoder for each connector by calling
1886 the connector <methodname>best_encoder</methodname> helper
1890 After locating the appropriate encoders, the helper function will
1891 call the <methodname>mode_fixup</methodname> encoder and CRTC helper
1892 operations to adjust the requested mode, or reject it completely in
1893 which case an error will be returned to the application. If the new
1894 configuration after mode adjustment is identical to the current
1895 configuration the helper function will return without performing any
1899 If the adjusted mode is identical to the current mode but changes to
1900 the frame buffer need to be applied, the
1901 <function>drm_crtc_helper_set_config</function> function will call
1902 the CRTC <methodname>mode_set_base</methodname> helper operation. If
1903 the adjusted mode differs from the current mode, or if the
1904 <methodname>mode_set_base</methodname> helper operation is not
1905 provided, the helper function performs a full mode set sequence by
1906 calling the <methodname>prepare</methodname>,
1907 <methodname>mode_set</methodname> and
1908 <methodname>commit</methodname> CRTC and encoder helper operations,
1913 <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
1915 The <function>drm_helper_connector_dpms</function> helper function
1916 is a connector <methodname>dpms</methodname> implementation that
1917 tracks power state of connectors. To use the function, drivers must
1918 provide <methodname>dpms</methodname> helper operations for CRTCs
1919 and encoders to apply the DPMS state to the device.
1922 The mid-layer doesn't track the power state of CRTCs and encoders.
1923 The <methodname>dpms</methodname> helper operations can thus be
1924 called with a mode identical to the currently active mode.
1928 <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
1929 uint32_t maxX, uint32_t maxY);</synopsis>
1931 The <function>drm_helper_probe_single_connector_modes</function> helper
1932 function is a connector <methodname>fill_modes</methodname>
1933 implementation that updates the connection status for the connector
1934 and then retrieves a list of modes by calling the connector
1935 <methodname>get_modes</methodname> helper operation.
1938 The function filters out modes larger than
1939 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1940 if specified. It then calls the optional connector
1941 <methodname>mode_valid</methodname> helper operation for each mode in
1942 the probed list to check whether the mode is valid for the connector.
1948 <title>CRTC Helper Operations</title>
1950 <listitem id="drm-helper-crtc-mode-fixup">
1951 <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
1952 const struct drm_display_mode *mode,
1953 struct drm_display_mode *adjusted_mode);</synopsis>
1955 Let CRTCs adjust the requested mode or reject it completely. This
1956 operation returns true if the mode is accepted (possibly after being
1957 adjusted) or false if it is rejected.
1960 The <methodname>mode_fixup</methodname> operation should reject the
1961 mode if it can't reasonably use it. The definition of "reasonable"
1962 is currently fuzzy in this context. One possible behaviour would be
1963 to set the adjusted mode to the panel timings when a fixed-mode
1964 panel is used with hardware capable of scaling. Another behaviour
1965 would be to accept any input mode and adjust it to the closest mode
1966 supported by the hardware (FIXME: This needs to be clarified).
1970 <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
1971 struct drm_framebuffer *old_fb)</synopsis>
1973 Move the CRTC on the current frame buffer (stored in
1974 <literal>crtc->fb</literal>) to position (x,y). Any of the frame
1975 buffer, x position or y position may have been modified.
1978 This helper operation is optional. If not provided, the
1979 <function>drm_crtc_helper_set_config</function> function will fall
1980 back to the <methodname>mode_set</methodname> helper operation.
1983 FIXME: Why are x and y passed as arguments, as they can be accessed
1984 through <literal>crtc->x</literal> and
1985 <literal>crtc->y</literal>?
1989 <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
1991 Prepare the CRTC for mode setting. This operation is called after
1992 validating the requested mode. Drivers use it to perform
1993 device-specific operations required before setting the new mode.
1997 <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
1998 struct drm_display_mode *adjusted_mode, int x, int y,
1999 struct drm_framebuffer *old_fb);</synopsis>
2001 Set a new mode, position and frame buffer. Depending on the device
2002 requirements, the mode can be stored internally by the driver and
2003 applied in the <methodname>commit</methodname> operation, or
2004 programmed to the hardware immediately.
2007 The <methodname>mode_set</methodname> operation returns 0 on success
2008 or a negative error code if an error occurs.
2012 <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
2014 Commit a mode. This operation is called after setting the new mode.
2015 Upon return the device must use the new mode and be fully
2022 <title>Encoder Helper Operations</title>
2025 <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
2026 const struct drm_display_mode *mode,
2027 struct drm_display_mode *adjusted_mode);</synopsis>
2029 Let encoders adjust the requested mode or reject it completely. This
2030 operation returns true if the mode is accepted (possibly after being
2031 adjusted) or false if it is rejected. See the
2032 <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
2033 operation</link> for an explanation of the allowed adjustments.
2037 <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
2039 Prepare the encoder for mode setting. This operation is called after
2040 validating the requested mode. Drivers use it to perform
2041 device-specific operations required before setting the new mode.
2045 <synopsis>void (*mode_set)(struct drm_encoder *encoder,
2046 struct drm_display_mode *mode,
2047 struct drm_display_mode *adjusted_mode);</synopsis>
2049 Set a new mode. Depending on the device requirements, the mode can
2050 be stored internally by the driver and applied in the
2051 <methodname>commit</methodname> operation, or programmed to the
2052 hardware immediately.
2056 <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
2058 Commit a mode. This operation is called after setting the new mode.
2059 Upon return the device must use the new mode and be fully
2066 <title>Connector Helper Operations</title>
2069 <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
2071 Return a pointer to the best encoder for the connecter. Device that
2072 map connectors to encoders 1:1 simply return the pointer to the
2073 associated encoder. This operation is mandatory.
2077 <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
2079 Fill the connector's <structfield>probed_modes</structfield> list
2080 by parsing EDID data with <function>drm_add_edid_modes</function> or
2081 calling <function>drm_mode_probed_add</function> directly for every
2082 supported mode and return the number of modes it has detected. This
2083 operation is mandatory.
2086 When adding modes manually the driver creates each mode with a call to
2087 <function>drm_mode_create</function> and must fill the following fields.
2090 <synopsis>__u32 type;</synopsis>
2092 Mode type bitmask, a combination of
2095 <term>DRM_MODE_TYPE_BUILTIN</term>
2096 <listitem><para>not used?</para></listitem>
2099 <term>DRM_MODE_TYPE_CLOCK_C</term>
2100 <listitem><para>not used?</para></listitem>
2103 <term>DRM_MODE_TYPE_CRTC_C</term>
2104 <listitem><para>not used?</para></listitem>
2108 DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
2111 <para>not used?</para>
2115 <term>DRM_MODE_TYPE_DEFAULT</term>
2116 <listitem><para>not used?</para></listitem>
2119 <term>DRM_MODE_TYPE_USERDEF</term>
2120 <listitem><para>not used?</para></listitem>
2123 <term>DRM_MODE_TYPE_DRIVER</term>
2126 The mode has been created by the driver (as opposed to
2127 to user-created modes).
2132 Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
2133 create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
2138 <synopsis>__u32 clock;</synopsis>
2139 <para>Pixel clock frequency in kHz unit</para>
2142 <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
2143 __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
2144 <para>Horizontal and vertical timing information</para>
2146 Active Front Sync Back
2148 <-----------------------><----------------><-------------><-------------->
2150 //////////////////////|
2151 ////////////////////// |
2152 ////////////////////// |.................. ................
2155 <----- [hv]display ----->
2156 <------------- [hv]sync_start ------------>
2157 <--------------------- [hv]sync_end --------------------->
2158 <-------------------------------- [hv]total ----------------------------->
2162 <synopsis>__u16 hskew;
2163 __u16 vscan;</synopsis>
2164 <para>Unknown</para>
2167 <synopsis>__u32 flags;</synopsis>
2169 Mode flags, a combination of
2172 <term>DRM_MODE_FLAG_PHSYNC</term>
2174 Horizontal sync is active high
2178 <term>DRM_MODE_FLAG_NHSYNC</term>
2180 Horizontal sync is active low
2184 <term>DRM_MODE_FLAG_PVSYNC</term>
2186 Vertical sync is active high
2190 <term>DRM_MODE_FLAG_NVSYNC</term>
2192 Vertical sync is active low
2196 <term>DRM_MODE_FLAG_INTERLACE</term>
2202 <term>DRM_MODE_FLAG_DBLSCAN</term>
2204 Mode uses doublescan
2208 <term>DRM_MODE_FLAG_CSYNC</term>
2210 Mode uses composite sync
2214 <term>DRM_MODE_FLAG_PCSYNC</term>
2216 Composite sync is active high
2220 <term>DRM_MODE_FLAG_NCSYNC</term>
2222 Composite sync is active low
2226 <term>DRM_MODE_FLAG_HSKEW</term>
2228 hskew provided (not used?)
2232 <term>DRM_MODE_FLAG_BCAST</term>
2238 <term>DRM_MODE_FLAG_PIXMUX</term>
2244 <term>DRM_MODE_FLAG_DBLCLK</term>
2250 <term>DRM_MODE_FLAG_CLKDIV2</term>
2258 Note that modes marked with the INTERLACE or DBLSCAN flags will be
2260 <function>drm_helper_probe_single_connector_modes</function> if
2261 the connector's <structfield>interlace_allowed</structfield> or
2262 <structfield>doublescan_allowed</structfield> field is set to 0.
2266 <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
2268 Mode name. The driver must call
2269 <function>drm_mode_set_name</function> to fill the mode name from
2270 <structfield>hdisplay</structfield>,
2271 <structfield>vdisplay</structfield> and interlace flag after
2272 filling the corresponding fields.
2278 The <structfield>vrefresh</structfield> value is computed by
2279 <function>drm_helper_probe_single_connector_modes</function>.
2282 When parsing EDID data, <function>drm_add_edid_modes</function> fill the
2283 connector <structfield>display_info</structfield>
2284 <structfield>width_mm</structfield> and
2285 <structfield>height_mm</structfield> fields. When creating modes
2286 manually the <methodname>get_modes</methodname> helper operation must
2287 set the <structfield>display_info</structfield>
2288 <structfield>width_mm</structfield> and
2289 <structfield>height_mm</structfield> fields if they haven't been set
2290 already (for instance at initialization time when a fixed-size panel is
2291 attached to the connector). The mode <structfield>width_mm</structfield>
2292 and <structfield>height_mm</structfield> fields are only used internally
2293 during EDID parsing and should not be set when creating modes manually.
2297 <synopsis>int (*mode_valid)(struct drm_connector *connector,
2298 struct drm_display_mode *mode);</synopsis>
2300 Verify whether a mode is valid for the connector. Return MODE_OK for
2301 supported modes and one of the enum drm_mode_status values (MODE_*)
2302 for unsupported modes. This operation is optional.
2305 As the mode rejection reason is currently not used beside for
2306 immediately removing the unsupported mode, an implementation can
2307 return MODE_BAD regardless of the exact reason why the mode is not
2311 Note that the <methodname>mode_valid</methodname> helper operation is
2312 only called for modes detected by the device, and
2313 <emphasis>not</emphasis> for modes set by the user through the CRTC
2314 <methodname>set_config</methodname> operation.
2320 <title>Modeset Helper Functions Reference</title>
2321 !Edrivers/gpu/drm/drm_crtc_helper.c
2324 <title>Output Probing Helper Functions Reference</title>
2325 !Pdrivers/gpu/drm/drm_probe_helper.c output probing helper overview
2326 !Edrivers/gpu/drm/drm_probe_helper.c
2329 <title>fbdev Helper Functions Reference</title>
2330 !Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers
2331 !Edrivers/gpu/drm/drm_fb_helper.c
2332 !Iinclude/drm/drm_fb_helper.h
2335 <title>Display Port Helper Functions Reference</title>
2336 !Pdrivers/gpu/drm/drm_dp_helper.c dp helpers
2337 !Iinclude/drm/drm_dp_helper.h
2338 !Edrivers/gpu/drm/drm_dp_helper.c
2341 <title>Display Port MST Helper Functions Reference</title>
2342 !Pdrivers/gpu/drm/drm_dp_mst_topology.c dp mst helper
2343 !Iinclude/drm/drm_dp_mst_helper.h
2344 !Edrivers/gpu/drm/drm_dp_mst_topology.c
2347 <title>EDID Helper Functions Reference</title>
2348 !Edrivers/gpu/drm/drm_edid.c
2351 <title>Rectangle Utilities Reference</title>
2352 !Pinclude/drm/drm_rect.h rect utils
2353 !Iinclude/drm/drm_rect.h
2354 !Edrivers/gpu/drm/drm_rect.c
2357 <title>Flip-work Helper Reference</title>
2358 !Pinclude/drm/drm_flip_work.h flip utils
2359 !Iinclude/drm/drm_flip_work.h
2360 !Edrivers/gpu/drm/drm_flip_work.c
2363 <title>HDMI Infoframes Helper Reference</title>
2365 Strictly speaking this is not a DRM helper library but generally useable
2366 by any driver interfacing with HDMI outputs like v4l or alsa drivers.
2367 But it nicely fits into the overall topic of mode setting helper
2368 libraries and hence is also included here.
2370 !Iinclude/linux/hdmi.h
2371 !Edrivers/video/hdmi.c
2374 <title id="drm-kms-planehelpers">Plane Helper Reference</title>
2375 !Edrivers/gpu/drm/drm_plane_helper.c Plane Helpers
2379 <!-- Internals: kms properties -->
2381 <sect1 id="drm-kms-properties">
2382 <title>KMS Properties</title>
2384 Drivers may need to expose additional parameters to applications than
2385 those described in the previous sections. KMS supports attaching
2386 properties to CRTCs, connectors and planes and offers a userspace API to
2387 list, get and set the property values.
2390 Properties are identified by a name that uniquely defines the property
2391 purpose, and store an associated value. For all property types except blob
2392 properties the value is a 64-bit unsigned integer.
2395 KMS differentiates between properties and property instances. Drivers
2396 first create properties and then create and associate individual instances
2397 of those properties to objects. A property can be instantiated multiple
2398 times and associated with different objects. Values are stored in property
2399 instances, and all other property information are stored in the property
2400 and shared between all instances of the property.
2403 Every property is created with a type that influences how the KMS core
2404 handles the property. Supported property types are
2407 <term>DRM_MODE_PROP_RANGE</term>
2408 <listitem><para>Range properties report their minimum and maximum
2409 admissible values. The KMS core verifies that values set by
2410 application fit in that range.</para></listitem>
2413 <term>DRM_MODE_PROP_ENUM</term>
2414 <listitem><para>Enumerated properties take a numerical value that
2415 ranges from 0 to the number of enumerated values defined by the
2416 property minus one, and associate a free-formed string name to each
2417 value. Applications can retrieve the list of defined value-name pairs
2418 and use the numerical value to get and set property instance values.
2422 <term>DRM_MODE_PROP_BITMASK</term>
2423 <listitem><para>Bitmask properties are enumeration properties that
2424 additionally restrict all enumerated values to the 0..63 range.
2425 Bitmask property instance values combine one or more of the
2426 enumerated bits defined by the property.</para></listitem>
2429 <term>DRM_MODE_PROP_BLOB</term>
2430 <listitem><para>Blob properties store a binary blob without any format
2431 restriction. The binary blobs are created as KMS standalone objects,
2432 and blob property instance values store the ID of their associated
2434 <para>Blob properties are only used for the connector EDID property
2435 and cannot be created by drivers.</para></listitem>
2440 To create a property drivers call one of the following functions depending
2441 on the property type. All property creation functions take property flags
2442 and name, as well as type-specific arguments.
2445 <synopsis>struct drm_property *drm_property_create_range(struct drm_device *dev, int flags,
2447 uint64_t min, uint64_t max);</synopsis>
2448 <para>Create a range property with the given minimum and maximum
2452 <synopsis>struct drm_property *drm_property_create_enum(struct drm_device *dev, int flags,
2454 const struct drm_prop_enum_list *props,
2455 int num_values);</synopsis>
2456 <para>Create an enumerated property. The <parameter>props</parameter>
2457 argument points to an array of <parameter>num_values</parameter>
2458 value-name pairs.</para>
2461 <synopsis>struct drm_property *drm_property_create_bitmask(struct drm_device *dev,
2462 int flags, const char *name,
2463 const struct drm_prop_enum_list *props,
2464 int num_values);</synopsis>
2465 <para>Create a bitmask property. The <parameter>props</parameter>
2466 argument points to an array of <parameter>num_values</parameter>
2467 value-name pairs.</para>
2472 Properties can additionally be created as immutable, in which case they
2473 will be read-only for applications but can be modified by the driver. To
2474 create an immutable property drivers must set the DRM_MODE_PROP_IMMUTABLE
2475 flag at property creation time.
2478 When no array of value-name pairs is readily available at property
2479 creation time for enumerated or range properties, drivers can create
2480 the property using the <function>drm_property_create</function> function
2481 and manually add enumeration value-name pairs by calling the
2482 <function>drm_property_add_enum</function> function. Care must be taken to
2483 properly specify the property type through the <parameter>flags</parameter>
2487 After creating properties drivers can attach property instances to CRTC,
2488 connector and plane objects by calling the
2489 <function>drm_object_attach_property</function>. The function takes a
2490 pointer to the target object, a pointer to the previously created property
2491 and an initial instance value.
2494 <title>Existing KMS Properties</title>
2496 The following table gives description of drm properties exposed by various
2499 <table border="1" cellpadding="0" cellspacing="0">
2501 <tr style="font-weight: bold;">
2502 <td valign="top" >Owner Module/Drivers</td>
2503 <td valign="top" >Group</td>
2504 <td valign="top" >Property Name</td>
2505 <td valign="top" >Type</td>
2506 <td valign="top" >Property Values</td>
2507 <td valign="top" >Object attached</td>
2508 <td valign="top" >Description/Restrictions</td>
2511 <td rowspan="21" valign="top" >DRM</td>
2512 <td rowspan="2" valign="top" >Generic</td>
2513 <td valign="top" >“EDID”</td>
2514 <td valign="top" >BLOB | IMMUTABLE</td>
2515 <td valign="top" >0</td>
2516 <td valign="top" >Connector</td>
2517 <td valign="top" >Contains id of edid blob ptr object.</td>
2520 <td valign="top" >“DPMS”</td>
2521 <td valign="top" >ENUM</td>
2522 <td valign="top" >{ “On”, “Standby”, “Suspend”, “Off” }</td>
2523 <td valign="top" >Connector</td>
2524 <td valign="top" >Contains DPMS operation mode value.</td>
2527 <td rowspan="1" valign="top" >Plane</td>
2528 <td valign="top" >“type”</td>
2529 <td valign="top" >ENUM | IMMUTABLE</td>
2530 <td valign="top" >{ "Overlay", "Primary", "Cursor" }</td>
2531 <td valign="top" >Plane</td>
2532 <td valign="top" >Plane type</td>
2535 <td rowspan="2" valign="top" >DVI-I</td>
2536 <td valign="top" >“subconnector”</td>
2537 <td valign="top" >ENUM</td>
2538 <td valign="top" >{ “Unknown”, “DVI-D”, “DVI-A” }</td>
2539 <td valign="top" >Connector</td>
2540 <td valign="top" >TBD</td>
2543 <td valign="top" >“select subconnector”</td>
2544 <td valign="top" >ENUM</td>
2545 <td valign="top" >{ “Automatic”, “DVI-D”, “DVI-A” }</td>
2546 <td valign="top" >Connector</td>
2547 <td valign="top" >TBD</td>
2550 <td rowspan="13" valign="top" >TV</td>
2551 <td valign="top" >“subconnector”</td>
2552 <td valign="top" >ENUM</td>
2553 <td valign="top" >{ "Unknown", "Composite", "SVIDEO", "Component", "SCART" }</td>
2554 <td valign="top" >Connector</td>
2555 <td valign="top" >TBD</td>
2558 <td valign="top" >“select subconnector”</td>
2559 <td valign="top" >ENUM</td>
2560 <td valign="top" >{ "Automatic", "Composite", "SVIDEO", "Component", "SCART" }</td>
2561 <td valign="top" >Connector</td>
2562 <td valign="top" >TBD</td>
2565 <td valign="top" >“mode”</td>
2566 <td valign="top" >ENUM</td>
2567 <td valign="top" >{ "NTSC_M", "NTSC_J", "NTSC_443", "PAL_B" } etc.</td>
2568 <td valign="top" >Connector</td>
2569 <td valign="top" >TBD</td>
2572 <td valign="top" >“left margin”</td>
2573 <td valign="top" >RANGE</td>
2574 <td valign="top" >Min=0, Max=100</td>
2575 <td valign="top" >Connector</td>
2576 <td valign="top" >TBD</td>
2579 <td valign="top" >“right margin”</td>
2580 <td valign="top" >RANGE</td>
2581 <td valign="top" >Min=0, Max=100</td>
2582 <td valign="top" >Connector</td>
2583 <td valign="top" >TBD</td>
2586 <td valign="top" >“top margin”</td>
2587 <td valign="top" >RANGE</td>
2588 <td valign="top" >Min=0, Max=100</td>
2589 <td valign="top" >Connector</td>
2590 <td valign="top" >TBD</td>
2593 <td valign="top" >“bottom margin”</td>
2594 <td valign="top" >RANGE</td>
2595 <td valign="top" >Min=0, Max=100</td>
2596 <td valign="top" >Connector</td>
2597 <td valign="top" >TBD</td>
2600 <td valign="top" >“brightness”</td>
2601 <td valign="top" >RANGE</td>
2602 <td valign="top" >Min=0, Max=100</td>
2603 <td valign="top" >Connector</td>
2604 <td valign="top" >TBD</td>
2607 <td valign="top" >“contrast”</td>
2608 <td valign="top" >RANGE</td>
2609 <td valign="top" >Min=0, Max=100</td>
2610 <td valign="top" >Connector</td>
2611 <td valign="top" >TBD</td>
2614 <td valign="top" >“flicker reduction”</td>
2615 <td valign="top" >RANGE</td>
2616 <td valign="top" >Min=0, Max=100</td>
2617 <td valign="top" >Connector</td>
2618 <td valign="top" >TBD</td>
2621 <td valign="top" >“overscan”</td>
2622 <td valign="top" >RANGE</td>
2623 <td valign="top" >Min=0, Max=100</td>
2624 <td valign="top" >Connector</td>
2625 <td valign="top" >TBD</td>
2628 <td valign="top" >“saturation”</td>
2629 <td valign="top" >RANGE</td>
2630 <td valign="top" >Min=0, Max=100</td>
2631 <td valign="top" >Connector</td>
2632 <td valign="top" >TBD</td>
2635 <td valign="top" >“hue”</td>
2636 <td valign="top" >RANGE</td>
2637 <td valign="top" >Min=0, Max=100</td>
2638 <td valign="top" >Connector</td>
2639 <td valign="top" >TBD</td>
2642 <td rowspan="3" valign="top" >Optional</td>
2643 <td valign="top" >“scaling mode”</td>
2644 <td valign="top" >ENUM</td>
2645 <td valign="top" >{ "None", "Full", "Center", "Full aspect" }</td>
2646 <td valign="top" >Connector</td>
2647 <td valign="top" >TBD</td>
2650 <td valign="top" >"aspect ratio"</td>
2651 <td valign="top" >ENUM</td>
2652 <td valign="top" >{ "None", "4:3", "16:9" }</td>
2653 <td valign="top" >Connector</td>
2654 <td valign="top" >DRM property to set aspect ratio from user space app.
2655 This enum is made generic to allow addition of custom aspect
2659 <td valign="top" >“dirty”</td>
2660 <td valign="top" >ENUM | IMMUTABLE</td>
2661 <td valign="top" >{ "Off", "On", "Annotate" }</td>
2662 <td valign="top" >Connector</td>
2663 <td valign="top" >TBD</td>
2666 <td rowspan="21" valign="top" >i915</td>
2667 <td rowspan="2" valign="top" >Generic</td>
2668 <td valign="top" >"Broadcast RGB"</td>
2669 <td valign="top" >ENUM</td>
2670 <td valign="top" >{ "Automatic", "Full", "Limited 16:235" }</td>
2671 <td valign="top" >Connector</td>
2672 <td valign="top" >TBD</td>
2675 <td valign="top" >“audio”</td>
2676 <td valign="top" >ENUM</td>
2677 <td valign="top" >{ "force-dvi", "off", "auto", "on" }</td>
2678 <td valign="top" >Connector</td>
2679 <td valign="top" >TBD</td>
2682 <td rowspan="1" valign="top" >Plane</td>
2683 <td valign="top" >“rotation”</td>
2684 <td valign="top" >BITMASK</td>
2685 <td valign="top" >{ 0, "rotate-0" }, { 2, "rotate-180" }</td>
2686 <td valign="top" >Plane</td>
2687 <td valign="top" >TBD</td>
2690 <td rowspan="17" valign="top" >SDVO-TV</td>
2691 <td valign="top" >“mode”</td>
2692 <td valign="top" >ENUM</td>
2693 <td valign="top" >{ "NTSC_M", "NTSC_J", "NTSC_443", "PAL_B" } etc.</td>
2694 <td valign="top" >Connector</td>
2695 <td valign="top" >TBD</td>
2698 <td valign="top" >"left_margin"</td>
2699 <td valign="top" >RANGE</td>
2700 <td valign="top" >Min=0, Max= SDVO dependent</td>
2701 <td valign="top" >Connector</td>
2702 <td valign="top" >TBD</td>
2705 <td valign="top" >"right_margin"</td>
2706 <td valign="top" >RANGE</td>
2707 <td valign="top" >Min=0, Max= SDVO dependent</td>
2708 <td valign="top" >Connector</td>
2709 <td valign="top" >TBD</td>
2712 <td valign="top" >"top_margin"</td>
2713 <td valign="top" >RANGE</td>
2714 <td valign="top" >Min=0, Max= SDVO dependent</td>
2715 <td valign="top" >Connector</td>
2716 <td valign="top" >TBD</td>
2719 <td valign="top" >"bottom_margin"</td>
2720 <td valign="top" >RANGE</td>
2721 <td valign="top" >Min=0, Max= SDVO dependent</td>
2722 <td valign="top" >Connector</td>
2723 <td valign="top" >TBD</td>
2726 <td valign="top" >“hpos”</td>
2727 <td valign="top" >RANGE</td>
2728 <td valign="top" >Min=0, Max= SDVO dependent</td>
2729 <td valign="top" >Connector</td>
2730 <td valign="top" >TBD</td>
2733 <td valign="top" >“vpos”</td>
2734 <td valign="top" >RANGE</td>
2735 <td valign="top" >Min=0, Max= SDVO dependent</td>
2736 <td valign="top" >Connector</td>
2737 <td valign="top" >TBD</td>
2740 <td valign="top" >“contrast”</td>
2741 <td valign="top" >RANGE</td>
2742 <td valign="top" >Min=0, Max= SDVO dependent</td>
2743 <td valign="top" >Connector</td>
2744 <td valign="top" >TBD</td>
2747 <td valign="top" >“saturation”</td>
2748 <td valign="top" >RANGE</td>
2749 <td valign="top" >Min=0, Max= SDVO dependent</td>
2750 <td valign="top" >Connector</td>
2751 <td valign="top" >TBD</td>
2754 <td valign="top" >“hue”</td>
2755 <td valign="top" >RANGE</td>
2756 <td valign="top" >Min=0, Max= SDVO dependent</td>
2757 <td valign="top" >Connector</td>
2758 <td valign="top" >TBD</td>
2761 <td valign="top" >“sharpness”</td>
2762 <td valign="top" >RANGE</td>
2763 <td valign="top" >Min=0, Max= SDVO dependent</td>
2764 <td valign="top" >Connector</td>
2765 <td valign="top" >TBD</td>
2768 <td valign="top" >“flicker_filter”</td>
2769 <td valign="top" >RANGE</td>
2770 <td valign="top" >Min=0, Max= SDVO dependent</td>
2771 <td valign="top" >Connector</td>
2772 <td valign="top" >TBD</td>
2775 <td valign="top" >“flicker_filter_adaptive”</td>
2776 <td valign="top" >RANGE</td>
2777 <td valign="top" >Min=0, Max= SDVO dependent</td>
2778 <td valign="top" >Connector</td>
2779 <td valign="top" >TBD</td>
2782 <td valign="top" >“flicker_filter_2d”</td>
2783 <td valign="top" >RANGE</td>
2784 <td valign="top" >Min=0, Max= SDVO dependent</td>
2785 <td valign="top" >Connector</td>
2786 <td valign="top" >TBD</td>
2789 <td valign="top" >“tv_chroma_filter”</td>
2790 <td valign="top" >RANGE</td>
2791 <td valign="top" >Min=0, Max= SDVO dependent</td>
2792 <td valign="top" >Connector</td>
2793 <td valign="top" >TBD</td>
2796 <td valign="top" >“tv_luma_filter”</td>
2797 <td valign="top" >RANGE</td>
2798 <td valign="top" >Min=0, Max= SDVO dependent</td>
2799 <td valign="top" >Connector</td>
2800 <td valign="top" >TBD</td>
2803 <td valign="top" >“dot_crawl”</td>
2804 <td valign="top" >RANGE</td>
2805 <td valign="top" >Min=0, Max=1</td>
2806 <td valign="top" >Connector</td>
2807 <td valign="top" >TBD</td>
2810 <td valign="top" >SDVO-TV/LVDS</td>
2811 <td valign="top" >“brightness”</td>
2812 <td valign="top" >RANGE</td>
2813 <td valign="top" >Min=0, Max= SDVO dependent</td>
2814 <td valign="top" >Connector</td>
2815 <td valign="top" >TBD</td>
2818 <td rowspan="2" valign="top" >CDV gma-500</td>
2819 <td rowspan="2" valign="top" >Generic</td>
2820 <td valign="top" >"Broadcast RGB"</td>
2821 <td valign="top" >ENUM</td>
2822 <td valign="top" >{ “Full”, “Limited 16:235” }</td>
2823 <td valign="top" >Connector</td>
2824 <td valign="top" >TBD</td>
2827 <td valign="top" >"Broadcast RGB"</td>
2828 <td valign="top" >ENUM</td>
2829 <td valign="top" >{ “off”, “auto”, “on” }</td>
2830 <td valign="top" >Connector</td>
2831 <td valign="top" >TBD</td>
2834 <td rowspan="19" valign="top" >Poulsbo</td>
2835 <td rowspan="1" valign="top" >Generic</td>
2836 <td valign="top" >“backlight”</td>
2837 <td valign="top" >RANGE</td>
2838 <td valign="top" >Min=0, Max=100</td>
2839 <td valign="top" >Connector</td>
2840 <td valign="top" >TBD</td>
2843 <td rowspan="17" valign="top" >SDVO-TV</td>
2844 <td valign="top" >“mode”</td>
2845 <td valign="top" >ENUM</td>
2846 <td valign="top" >{ "NTSC_M", "NTSC_J", "NTSC_443", "PAL_B" } etc.</td>
2847 <td valign="top" >Connector</td>
2848 <td valign="top" >TBD</td>
2851 <td valign="top" >"left_margin"</td>
2852 <td valign="top" >RANGE</td>
2853 <td valign="top" >Min=0, Max= SDVO dependent</td>
2854 <td valign="top" >Connector</td>
2855 <td valign="top" >TBD</td>
2858 <td valign="top" >"right_margin"</td>
2859 <td valign="top" >RANGE</td>
2860 <td valign="top" >Min=0, Max= SDVO dependent</td>
2861 <td valign="top" >Connector</td>
2862 <td valign="top" >TBD</td>
2865 <td valign="top" >"top_margin"</td>
2866 <td valign="top" >RANGE</td>
2867 <td valign="top" >Min=0, Max= SDVO dependent</td>
2868 <td valign="top" >Connector</td>
2869 <td valign="top" >TBD</td>
2872 <td valign="top" >"bottom_margin"</td>
2873 <td valign="top" >RANGE</td>
2874 <td valign="top" >Min=0, Max= SDVO dependent</td>
2875 <td valign="top" >Connector</td>
2876 <td valign="top" >TBD</td>
2879 <td valign="top" >“hpos”</td>
2880 <td valign="top" >RANGE</td>
2881 <td valign="top" >Min=0, Max= SDVO dependent</td>
2882 <td valign="top" >Connector</td>
2883 <td valign="top" >TBD</td>
2886 <td valign="top" >“vpos”</td>
2887 <td valign="top" >RANGE</td>
2888 <td valign="top" >Min=0, Max= SDVO dependent</td>
2889 <td valign="top" >Connector</td>
2890 <td valign="top" >TBD</td>
2893 <td valign="top" >“contrast”</td>
2894 <td valign="top" >RANGE</td>
2895 <td valign="top" >Min=0, Max= SDVO dependent</td>
2896 <td valign="top" >Connector</td>
2897 <td valign="top" >TBD</td>
2900 <td valign="top" >“saturation”</td>
2901 <td valign="top" >RANGE</td>
2902 <td valign="top" >Min=0, Max= SDVO dependent</td>
2903 <td valign="top" >Connector</td>
2904 <td valign="top" >TBD</td>
2907 <td valign="top" >“hue”</td>
2908 <td valign="top" >RANGE</td>
2909 <td valign="top" >Min=0, Max= SDVO dependent</td>
2910 <td valign="top" >Connector</td>
2911 <td valign="top" >TBD</td>
2914 <td valign="top" >“sharpness”</td>
2915 <td valign="top" >RANGE</td>
2916 <td valign="top" >Min=0, Max= SDVO dependent</td>
2917 <td valign="top" >Connector</td>
2918 <td valign="top" >TBD</td>
2921 <td valign="top" >“flicker_filter”</td>
2922 <td valign="top" >RANGE</td>
2923 <td valign="top" >Min=0, Max= SDVO dependent</td>
2924 <td valign="top" >Connector</td>
2925 <td valign="top" >TBD</td>
2928 <td valign="top" >“flicker_filter_adaptive”</td>
2929 <td valign="top" >RANGE</td>
2930 <td valign="top" >Min=0, Max= SDVO dependent</td>
2931 <td valign="top" >Connector</td>
2932 <td valign="top" >TBD</td>
2935 <td valign="top" >“flicker_filter_2d”</td>
2936 <td valign="top" >RANGE</td>
2937 <td valign="top" >Min=0, Max= SDVO dependent</td>
2938 <td valign="top" >Connector</td>
2939 <td valign="top" >TBD</td>
2942 <td valign="top" >“tv_chroma_filter”</td>
2943 <td valign="top" >RANGE</td>
2944 <td valign="top" >Min=0, Max= SDVO dependent</td>
2945 <td valign="top" >Connector</td>
2946 <td valign="top" >TBD</td>
2949 <td valign="top" >“tv_luma_filter”</td>
2950 <td valign="top" >RANGE</td>
2951 <td valign="top" >Min=0, Max= SDVO dependent</td>
2952 <td valign="top" >Connector</td>
2953 <td valign="top" >TBD</td>
2956 <td valign="top" >“dot_crawl”</td>
2957 <td valign="top" >RANGE</td>
2958 <td valign="top" >Min=0, Max=1</td>
2959 <td valign="top" >Connector</td>
2960 <td valign="top" >TBD</td>
2963 <td valign="top" >SDVO-TV/LVDS</td>
2964 <td valign="top" >“brightness”</td>
2965 <td valign="top" >RANGE</td>
2966 <td valign="top" >Min=0, Max= SDVO dependent</td>
2967 <td valign="top" >Connector</td>
2968 <td valign="top" >TBD</td>
2971 <td rowspan="11" valign="top" >armada</td>
2972 <td rowspan="2" valign="top" >CRTC</td>
2973 <td valign="top" >"CSC_YUV"</td>
2974 <td valign="top" >ENUM</td>
2975 <td valign="top" >{ "Auto" , "CCIR601", "CCIR709" }</td>
2976 <td valign="top" >CRTC</td>
2977 <td valign="top" >TBD</td>
2980 <td valign="top" >"CSC_RGB"</td>
2981 <td valign="top" >ENUM</td>
2982 <td valign="top" >{ "Auto", "Computer system", "Studio" }</td>
2983 <td valign="top" >CRTC</td>
2984 <td valign="top" >TBD</td>
2987 <td rowspan="9" valign="top" >Overlay</td>
2988 <td valign="top" >"colorkey"</td>
2989 <td valign="top" >RANGE</td>
2990 <td valign="top" >Min=0, Max=0xffffff</td>
2991 <td valign="top" >Plane</td>
2992 <td valign="top" >TBD</td>
2995 <td valign="top" >"colorkey_min"</td>
2996 <td valign="top" >RANGE</td>
2997 <td valign="top" >Min=0, Max=0xffffff</td>
2998 <td valign="top" >Plane</td>
2999 <td valign="top" >TBD</td>
3002 <td valign="top" >"colorkey_max"</td>
3003 <td valign="top" >RANGE</td>
3004 <td valign="top" >Min=0, Max=0xffffff</td>
3005 <td valign="top" >Plane</td>
3006 <td valign="top" >TBD</td>
3009 <td valign="top" >"colorkey_val"</td>
3010 <td valign="top" >RANGE</td>
3011 <td valign="top" >Min=0, Max=0xffffff</td>
3012 <td valign="top" >Plane</td>
3013 <td valign="top" >TBD</td>
3016 <td valign="top" >"colorkey_alpha"</td>
3017 <td valign="top" >RANGE</td>
3018 <td valign="top" >Min=0, Max=0xffffff</td>
3019 <td valign="top" >Plane</td>
3020 <td valign="top" >TBD</td>
3023 <td valign="top" >"colorkey_mode"</td>
3024 <td valign="top" >ENUM</td>
3025 <td valign="top" >{ "disabled", "Y component", "U component"
3026 , "V component", "RGB", “R component", "G component", "B component" }</td>
3027 <td valign="top" >Plane</td>
3028 <td valign="top" >TBD</td>
3031 <td valign="top" >"brightness"</td>
3032 <td valign="top" >RANGE</td>
3033 <td valign="top" >Min=0, Max=256 + 255</td>
3034 <td valign="top" >Plane</td>
3035 <td valign="top" >TBD</td>
3038 <td valign="top" >"contrast"</td>
3039 <td valign="top" >RANGE</td>
3040 <td valign="top" >Min=0, Max=0x7fff</td>
3041 <td valign="top" >Plane</td>
3042 <td valign="top" >TBD</td>
3045 <td valign="top" >"saturation"</td>
3046 <td valign="top" >RANGE</td>
3047 <td valign="top" >Min=0, Max=0x7fff</td>
3048 <td valign="top" >Plane</td>
3049 <td valign="top" >TBD</td>
3052 <td rowspan="2" valign="top" >exynos</td>
3053 <td valign="top" >CRTC</td>
3054 <td valign="top" >“mode”</td>
3055 <td valign="top" >ENUM</td>
3056 <td valign="top" >{ "normal", "blank" }</td>
3057 <td valign="top" >CRTC</td>
3058 <td valign="top" >TBD</td>
3061 <td valign="top" >Overlay</td>
3062 <td valign="top" >“zpos”</td>
3063 <td valign="top" >RANGE</td>
3064 <td valign="top" >Min=0, Max=MAX_PLANE-1</td>
3065 <td valign="top" >Plane</td>
3066 <td valign="top" >TBD</td>
3069 <td rowspan="2" valign="top" >i2c/ch7006_drv</td>
3070 <td valign="top" >Generic</td>
3071 <td valign="top" >“scale”</td>
3072 <td valign="top" >RANGE</td>
3073 <td valign="top" >Min=0, Max=2</td>
3074 <td valign="top" >Connector</td>
3075 <td valign="top" >TBD</td>
3078 <td rowspan="1" valign="top" >TV</td>
3079 <td valign="top" >“mode”</td>
3080 <td valign="top" >ENUM</td>
3081 <td valign="top" >{ "PAL", "PAL-M","PAL-N"}, ”PAL-Nc"
3082 , "PAL-60", "NTSC-M", "NTSC-J" }</td>
3083 <td valign="top" >Connector</td>
3084 <td valign="top" >TBD</td>
3087 <td rowspan="15" valign="top" >nouveau</td>
3088 <td rowspan="6" valign="top" >NV10 Overlay</td>
3089 <td valign="top" >"colorkey"</td>
3090 <td valign="top" >RANGE</td>
3091 <td valign="top" >Min=0, Max=0x01ffffff</td>
3092 <td valign="top" >Plane</td>
3093 <td valign="top" >TBD</td>
3096 <td valign="top" >“contrast”</td>
3097 <td valign="top" >RANGE</td>
3098 <td valign="top" >Min=0, Max=8192-1</td>
3099 <td valign="top" >Plane</td>
3100 <td valign="top" >TBD</td>
3103 <td valign="top" >“brightness”</td>
3104 <td valign="top" >RANGE</td>
3105 <td valign="top" >Min=0, Max=1024</td>
3106 <td valign="top" >Plane</td>
3107 <td valign="top" >TBD</td>
3110 <td valign="top" >“hue”</td>
3111 <td valign="top" >RANGE</td>
3112 <td valign="top" >Min=0, Max=359</td>
3113 <td valign="top" >Plane</td>
3114 <td valign="top" >TBD</td>
3117 <td valign="top" >“saturation”</td>
3118 <td valign="top" >RANGE</td>
3119 <td valign="top" >Min=0, Max=8192-1</td>
3120 <td valign="top" >Plane</td>
3121 <td valign="top" >TBD</td>
3124 <td valign="top" >“iturbt_709”</td>
3125 <td valign="top" >RANGE</td>
3126 <td valign="top" >Min=0, Max=1</td>
3127 <td valign="top" >Plane</td>
3128 <td valign="top" >TBD</td>
3131 <td rowspan="2" valign="top" >Nv04 Overlay</td>
3132 <td valign="top" >“colorkey”</td>
3133 <td valign="top" >RANGE</td>
3134 <td valign="top" >Min=0, Max=0x01ffffff</td>
3135 <td valign="top" >Plane</td>
3136 <td valign="top" >TBD</td>
3139 <td valign="top" >“brightness”</td>
3140 <td valign="top" >RANGE</td>
3141 <td valign="top" >Min=0, Max=1024</td>
3142 <td valign="top" >Plane</td>
3143 <td valign="top" >TBD</td>
3146 <td rowspan="7" valign="top" >Display</td>
3147 <td valign="top" >“dithering mode”</td>
3148 <td valign="top" >ENUM</td>
3149 <td valign="top" >{ "auto", "off", "on" }</td>
3150 <td valign="top" >Connector</td>
3151 <td valign="top" >TBD</td>
3154 <td valign="top" >“dithering depth”</td>
3155 <td valign="top" >ENUM</td>
3156 <td valign="top" >{ "auto", "off", "on", "static 2x2", "dynamic 2x2", "temporal" }</td>
3157 <td valign="top" >Connector</td>
3158 <td valign="top" >TBD</td>
3161 <td valign="top" >“underscan”</td>
3162 <td valign="top" >ENUM</td>
3163 <td valign="top" >{ "auto", "6 bpc", "8 bpc" }</td>
3164 <td valign="top" >Connector</td>
3165 <td valign="top" >TBD</td>
3168 <td valign="top" >“underscan hborder”</td>
3169 <td valign="top" >RANGE</td>
3170 <td valign="top" >Min=0, Max=128</td>
3171 <td valign="top" >Connector</td>
3172 <td valign="top" >TBD</td>
3175 <td valign="top" >“underscan vborder”</td>
3176 <td valign="top" >RANGE</td>
3177 <td valign="top" >Min=0, Max=128</td>
3178 <td valign="top" >Connector</td>
3179 <td valign="top" >TBD</td>
3182 <td valign="top" >“vibrant hue”</td>
3183 <td valign="top" >RANGE</td>
3184 <td valign="top" >Min=0, Max=180</td>
3185 <td valign="top" >Connector</td>
3186 <td valign="top" >TBD</td>
3189 <td valign="top" >“color vibrance”</td>
3190 <td valign="top" >RANGE</td>
3191 <td valign="top" >Min=0, Max=200</td>
3192 <td valign="top" >Connector</td>
3193 <td valign="top" >TBD</td>
3196 <td rowspan="2" valign="top" >omap</td>
3197 <td rowspan="2" valign="top" >Generic</td>
3198 <td valign="top" >“rotation”</td>
3199 <td valign="top" >BITMASK</td>
3200 <td valign="top" >{ 0, "rotate-0" },
3202 { 2, "rotate-180" },
3203 { 3, "rotate-270" },
3205 { 5, "reflect-y" }</td>
3206 <td valign="top" >CRTC, Plane</td>
3207 <td valign="top" >TBD</td>
3210 <td valign="top" >“zorder”</td>
3211 <td valign="top" >RANGE</td>
3212 <td valign="top" >Min=0, Max=3</td>
3213 <td valign="top" >CRTC, Plane</td>
3214 <td valign="top" >TBD</td>
3217 <td valign="top" >qxl</td>
3218 <td valign="top" >Generic</td>
3219 <td valign="top" >“hotplug_mode_update"</td>
3220 <td valign="top" >RANGE</td>
3221 <td valign="top" >Min=0, Max=1</td>
3222 <td valign="top" >Connector</td>
3223 <td valign="top" >TBD</td>
3226 <td rowspan="9" valign="top" >radeon</td>
3227 <td valign="top" >DVI-I</td>
3228 <td valign="top" >“coherent”</td>
3229 <td valign="top" >RANGE</td>
3230 <td valign="top" >Min=0, Max=1</td>
3231 <td valign="top" >Connector</td>
3232 <td valign="top" >TBD</td>
3235 <td valign="top" >DAC enable load detect</td>
3236 <td valign="top" >“load detection”</td>
3237 <td valign="top" >RANGE</td>
3238 <td valign="top" >Min=0, Max=1</td>
3239 <td valign="top" >Connector</td>
3240 <td valign="top" >TBD</td>
3243 <td valign="top" >TV Standard</td>
3244 <td valign="top" >"tv standard"</td>
3245 <td valign="top" >ENUM</td>
3246 <td valign="top" >{ "ntsc", "pal", "pal-m", "pal-60", "ntsc-j"
3247 , "scart-pal", "pal-cn", "secam" }</td>
3248 <td valign="top" >Connector</td>
3249 <td valign="top" >TBD</td>
3252 <td valign="top" >legacy TMDS PLL detect</td>
3253 <td valign="top" >"tmds_pll"</td>
3254 <td valign="top" >ENUM</td>
3255 <td valign="top" >{ "driver", "bios" }</td>
3256 <td valign="top" >-</td>
3257 <td valign="top" >TBD</td>
3260 <td rowspan="3" valign="top" >Underscan</td>
3261 <td valign="top" >"underscan"</td>
3262 <td valign="top" >ENUM</td>
3263 <td valign="top" >{ "off", "on", "auto" }</td>
3264 <td valign="top" >Connector</td>
3265 <td valign="top" >TBD</td>
3268 <td valign="top" >"underscan hborder"</td>
3269 <td valign="top" >RANGE</td>
3270 <td valign="top" >Min=0, Max=128</td>
3271 <td valign="top" >Connector</td>
3272 <td valign="top" >TBD</td>
3275 <td valign="top" >"underscan vborder"</td>
3276 <td valign="top" >RANGE</td>
3277 <td valign="top" >Min=0, Max=128</td>
3278 <td valign="top" >Connector</td>
3279 <td valign="top" >TBD</td>
3282 <td valign="top" >Audio</td>
3283 <td valign="top" >“audio”</td>
3284 <td valign="top" >ENUM</td>
3285 <td valign="top" >{ "off", "on", "auto" }</td>
3286 <td valign="top" >Connector</td>
3287 <td valign="top" >TBD</td>
3290 <td valign="top" >FMT Dithering</td>
3291 <td valign="top" >“dither”</td>
3292 <td valign="top" >ENUM</td>
3293 <td valign="top" >{ "off", "on" }</td>
3294 <td valign="top" >Connector</td>
3295 <td valign="top" >TBD</td>
3298 <td rowspan="3" valign="top" >rcar-du</td>
3299 <td rowspan="3" valign="top" >Generic</td>
3300 <td valign="top" >"alpha"</td>
3301 <td valign="top" >RANGE</td>
3302 <td valign="top" >Min=0, Max=255</td>
3303 <td valign="top" >Plane</td>
3304 <td valign="top" >TBD</td>
3307 <td valign="top" >"colorkey"</td>
3308 <td valign="top" >RANGE</td>
3309 <td valign="top" >Min=0, Max=0x01ffffff</td>
3310 <td valign="top" >Plane</td>
3311 <td valign="top" >TBD</td>
3314 <td valign="top" >"zpos"</td>
3315 <td valign="top" >RANGE</td>
3316 <td valign="top" >Min=1, Max=7</td>
3317 <td valign="top" >Plane</td>
3318 <td valign="top" >TBD</td>
3325 <!-- Internals: vertical blanking -->
3327 <sect1 id="drm-vertical-blank">
3328 <title>Vertical Blanking</title>
3330 Vertical blanking plays a major role in graphics rendering. To achieve
3331 tear-free display, users must synchronize page flips and/or rendering to
3332 vertical blanking. The DRM API offers ioctls to perform page flips
3333 synchronized to vertical blanking and wait for vertical blanking.
3336 The DRM core handles most of the vertical blanking management logic, which
3337 involves filtering out spurious interrupts, keeping race-free blanking
3338 counters, coping with counter wrap-around and resets and keeping use
3339 counts. It relies on the driver to generate vertical blanking interrupts
3340 and optionally provide a hardware vertical blanking counter. Drivers must
3341 implement the following operations.
3345 <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
3346 void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
3348 Enable or disable vertical blanking interrupts for the given CRTC.
3352 <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
3354 Retrieve the value of the vertical blanking counter for the given
3355 CRTC. If the hardware maintains a vertical blanking counter its value
3356 should be returned. Otherwise drivers can use the
3357 <function>drm_vblank_count</function> helper function to handle this
3363 Drivers must initialize the vertical blanking handling core with a call to
3364 <function>drm_vblank_init</function> in their
3365 <methodname>load</methodname> operation. The function will set the struct
3366 <structname>drm_device</structname>
3367 <structfield>vblank_disable_allowed</structfield> field to 0. This will
3368 keep vertical blanking interrupts enabled permanently until the first mode
3369 set operation, where <structfield>vblank_disable_allowed</structfield> is
3370 set to 1. The reason behind this is not clear. Drivers can set the field
3371 to 1 after <function>calling drm_vblank_init</function> to make vertical
3372 blanking interrupts dynamically managed from the beginning.
3375 Vertical blanking interrupts can be enabled by the DRM core or by drivers
3376 themselves (for instance to handle page flipping operations). The DRM core
3377 maintains a vertical blanking use count to ensure that the interrupts are
3378 not disabled while a user still needs them. To increment the use count,
3379 drivers call <function>drm_vblank_get</function>. Upon return vertical
3380 blanking interrupts are guaranteed to be enabled.
3383 To decrement the use count drivers call
3384 <function>drm_vblank_put</function>. Only when the use count drops to zero
3385 will the DRM core disable the vertical blanking interrupts after a delay
3386 by scheduling a timer. The delay is accessible through the vblankoffdelay
3387 module parameter or the <varname>drm_vblank_offdelay</varname> global
3388 variable and expressed in milliseconds. Its default value is 5000 ms.
3391 When a vertical blanking interrupt occurs drivers only need to call the
3392 <function>drm_handle_vblank</function> function to account for the
3396 Resources allocated by <function>drm_vblank_init</function> must be freed
3397 with a call to <function>drm_vblank_cleanup</function> in the driver
3398 <methodname>unload</methodname> operation handler.
3401 <title>Vertical Blanking and Interrupt Handling Functions Reference</title>
3402 !Edrivers/gpu/drm/drm_irq.c
3403 !Iinclude/drm/drmP.h drm_crtc_vblank_waitqueue
3407 <!-- Internals: open/close, file operations and ioctls -->
3410 <title>Open/Close, File Operations and IOCTLs</title>
3412 <title>Open and Close</title>
3413 <synopsis>int (*firstopen) (struct drm_device *);
3414 void (*lastclose) (struct drm_device *);
3415 int (*open) (struct drm_device *, struct drm_file *);
3416 void (*preclose) (struct drm_device *, struct drm_file *);
3417 void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
3418 <abstract>Open and close handlers. None of those methods are mandatory.
3421 The <methodname>firstopen</methodname> method is called by the DRM core
3422 for legacy UMS (User Mode Setting) drivers only when an application
3423 opens a device that has no other opened file handle. UMS drivers can
3424 implement it to acquire device resources. KMS drivers can't use the
3425 method and must acquire resources in the <methodname>load</methodname>
3429 Similarly the <methodname>lastclose</methodname> method is called when
3430 the last application holding a file handle opened on the device closes
3431 it, for both UMS and KMS drivers. Additionally, the method is also
3432 called at module unload time or, for hot-pluggable devices, when the
3433 device is unplugged. The <methodname>firstopen</methodname> and
3434 <methodname>lastclose</methodname> calls can thus be unbalanced.
3437 The <methodname>open</methodname> method is called every time the device
3438 is opened by an application. Drivers can allocate per-file private data
3439 in this method and store them in the struct
3440 <structname>drm_file</structname> <structfield>driver_priv</structfield>
3441 field. Note that the <methodname>open</methodname> method is called
3442 before <methodname>firstopen</methodname>.
3445 The close operation is split into <methodname>preclose</methodname> and
3446 <methodname>postclose</methodname> methods. Drivers must stop and
3447 cleanup all per-file operations in the <methodname>preclose</methodname>
3448 method. For instance pending vertical blanking and page flip events must
3449 be cancelled. No per-file operation is allowed on the file handle after
3450 returning from the <methodname>preclose</methodname> method.
3453 Finally the <methodname>postclose</methodname> method is called as the
3454 last step of the close operation, right before calling the
3455 <methodname>lastclose</methodname> method if no other open file handle
3456 exists for the device. Drivers that have allocated per-file private data
3457 in the <methodname>open</methodname> method should free it here.
3460 The <methodname>lastclose</methodname> method should restore CRTC and
3461 plane properties to default value, so that a subsequent open of the
3462 device will not inherit state from the previous user. It can also be
3463 used to execute delayed power switching state changes, e.g. in
3464 conjunction with the vga-switcheroo infrastructure. Beyond that KMS
3465 drivers should not do any further cleanup. Only legacy UMS drivers might
3466 need to clean up device state so that the vga console or an independent
3467 fbdev driver could take over.
3471 <title>File Operations</title>
3472 <synopsis>const struct file_operations *fops</synopsis>
3473 <abstract>File operations for the DRM device node.</abstract>
3475 Drivers must define the file operations structure that forms the DRM
3476 userspace API entry point, even though most of those operations are
3477 implemented in the DRM core. The <methodname>open</methodname>,
3478 <methodname>release</methodname> and <methodname>ioctl</methodname>
3479 operations are handled by
3481 .owner = THIS_MODULE,
3483 .release = drm_release,
3484 .unlocked_ioctl = drm_ioctl,
3485 #ifdef CONFIG_COMPAT
3486 .compat_ioctl = drm_compat_ioctl,
3491 Drivers that implement private ioctls that requires 32/64bit
3492 compatibility support must provide their own
3493 <methodname>compat_ioctl</methodname> handler that processes private
3494 ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
3497 The <methodname>read</methodname> and <methodname>poll</methodname>
3498 operations provide support for reading DRM events and polling them. They
3503 .llseek = no_llseek,
3507 The memory mapping implementation varies depending on how the driver
3508 manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
3509 while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
3510 <xref linkend="drm-gem"/>.
3512 .mmap = drm_gem_mmap,
3516 No other file operation is supported by the DRM API.
3520 <title>IOCTLs</title>
3521 <synopsis>struct drm_ioctl_desc *ioctls;
3522 int num_ioctls;</synopsis>
3523 <abstract>Driver-specific ioctls descriptors table.</abstract>
3525 Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
3526 descriptors table is indexed by the ioctl number offset from the base
3527 value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
3531 <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
3533 <parameter>ioctl</parameter> is the ioctl name. Drivers must define
3534 the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
3535 offset from DRM_COMMAND_BASE and the ioctl number respectively. The
3536 first macro is private to the device while the second must be exposed
3537 to userspace in a public header.
3540 <parameter>func</parameter> is a pointer to the ioctl handler function
3541 compatible with the <type>drm_ioctl_t</type> type.
3542 <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
3543 struct drm_file *file_priv);</programlisting>
3546 <parameter>flags</parameter> is a bitmask combination of the following
3547 values. It restricts how the ioctl is allowed to be called.
3550 DRM_AUTH - Only authenticated callers allowed
3553 DRM_MASTER - The ioctl can only be called on the master file
3557 DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
3560 DRM_CONTROL_ALLOW - The ioctl can only be called on a control
3564 DRM_UNLOCKED - The ioctl handler will be called without locking
3565 the DRM global mutex
3573 <title>Legacy Support Code</title>
3575 The section very briefly covers some of the old legacy support code which
3576 is only used by old DRM drivers which have done a so-called shadow-attach
3577 to the underlying device instead of registering as a real driver. This
3578 also includes some of the old generic buffer management and command
3579 submission code. Do not use any of this in new and modern drivers.
3583 <title>Legacy Suspend/Resume</title>
3585 The DRM core provides some suspend/resume code, but drivers wanting full
3586 suspend/resume support should provide save() and restore() functions.
3587 These are called at suspend, hibernate, or resume time, and should perform
3588 any state save or restore required by your device across suspend or
3591 <synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
3592 int (*resume) (struct drm_device *);</synopsis>
3594 Those are legacy suspend and resume methods which
3595 <emphasis>only</emphasis> work with the legacy shadow-attach driver
3596 registration functions. New driver should use the power management
3597 interface provided by their bus type (usually through
3598 the struct <structname>device_driver</structname> dev_pm_ops) and set
3599 these methods to NULL.
3604 <title>Legacy DMA Services</title>
3606 This should cover how DMA mapping etc. is supported by the core.
3607 These functions are deprecated and should not be used.
3616 - Document the struct_mutex catch-all lock
3617 - Document connector properties
3619 - Why is the load method optional?
3620 - What are drivers supposed to set the initial display state to, and how?
3621 Connector's DPMS states are not initialized and are thus equal to
3622 DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
3623 drm_helper_disable_unused_functions(), which disables unused encoders and
3624 CRTCs, but doesn't touch the connectors' DPMS state, and
3625 drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
3626 that don't implement (or just don't use) fbcon compatibility need to call
3627 those functions themselves?
3628 - KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
3629 around mode setting. Should this be done in the DRM core?
3630 - vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
3631 call and never set back to 0. It seems to be safe to permanently set it to 1
3632 in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
3633 well. This should be investigated.
3634 - crtc and connector .save and .restore operations are only used internally in
3635 drivers, should they be removed from the core?
3636 - encoder mid-layer .save and .restore operations are only used internally in
3637 drivers, should they be removed from the core?
3638 - encoder mid-layer .detect operation is only used internally in drivers,
3639 should it be removed from the core?
3642 <!-- External interfaces -->
3644 <chapter id="drmExternals">
3645 <title>Userland interfaces</title>
3647 The DRM core exports several interfaces to applications,
3648 generally intended to be used through corresponding libdrm
3649 wrapper functions. In addition, drivers export device-specific
3650 interfaces for use by userspace drivers & device-aware
3651 applications through ioctls and sysfs files.
3654 External interfaces include: memory mapping, context management,
3655 DMA operations, AGP management, vblank control, fence
3656 management, memory management, and output management.
3659 Cover generic ioctls and sysfs layout here. We only need high-level
3660 info, since man pages should cover the rest.
3663 <!-- External: render nodes -->
3666 <title>Render nodes</title>
3668 DRM core provides multiple character-devices for user-space to use.
3669 Depending on which device is opened, user-space can perform a different
3670 set of operations (mainly ioctls). The primary node is always created
3671 and called card<num>. Additionally, a currently
3672 unused control node, called controlD<num> is also
3673 created. The primary node provides all legacy operations and
3674 historically was the only interface used by userspace. With KMS, the
3675 control node was introduced. However, the planned KMS control interface
3676 has never been written and so the control node stays unused to date.
3679 With the increased use of offscreen renderers and GPGPU applications,
3680 clients no longer require running compositors or graphics servers to
3681 make use of a GPU. But the DRM API required unprivileged clients to
3682 authenticate to a DRM-Master prior to getting GPU access. To avoid this
3683 step and to grant clients GPU access without authenticating, render
3684 nodes were introduced. Render nodes solely serve render clients, that
3685 is, no modesetting or privileged ioctls can be issued on render nodes.
3686 Only non-global rendering commands are allowed. If a driver supports
3687 render nodes, it must advertise it via the DRIVER_RENDER
3688 DRM driver capability. If not supported, the primary node must be used
3689 for render clients together with the legacy drmAuth authentication
3693 If a driver advertises render node support, DRM core will create a
3694 separate render node called renderD<num>. There will
3695 be one render node per device. No ioctls except PRIME-related ioctls
3696 will be allowed on this node. Especially GEM_OPEN will be
3697 explicitly prohibited. Render nodes are designed to avoid the
3698 buffer-leaks, which occur if clients guess the flink names or mmap
3699 offsets on the legacy interface. Additionally to this basic interface,
3700 drivers must mark their driver-dependent render-only ioctls as
3701 DRM_RENDER_ALLOW so render clients can use them. Driver
3702 authors must be careful not to allow any privileged ioctls on render
3706 With render nodes, user-space can now control access to the render node
3707 via basic file-system access-modes. A running graphics server which
3708 authenticates clients on the privileged primary/legacy node is no longer
3709 required. Instead, a client can open the render node and is immediately
3710 granted GPU access. Communication between clients (or servers) is done
3711 via PRIME. FLINK from render node to legacy node is not supported. New
3712 clients must not use the insecure FLINK interface.
3715 Besides dropping all modeset/global ioctls, render nodes also drop the
3716 DRM-Master concept. There is no reason to associate render clients with
3717 a DRM-Master as they are independent of any graphics server. Besides,
3718 they must work without any running master, anyway.
3719 Drivers must be able to run without a master object if they support
3720 render nodes. If, on the other hand, a driver requires shared state
3721 between clients which is visible to user-space and accessible beyond
3722 open-file boundaries, they cannot support render nodes.
3726 <!-- External: vblank handling -->
3729 <title>VBlank event handling</title>
3731 The DRM core exposes two vertical blank related ioctls:
3734 <term>DRM_IOCTL_WAIT_VBLANK</term>
3737 This takes a struct drm_wait_vblank structure as its argument,
3738 and it is used to block or request a signal when a specified
3739 vblank event occurs.
3744 <term>DRM_IOCTL_MODESET_CTL</term>
3747 This was only used for user-mode-settind drivers around
3748 modesetting changes to allow the kernel to update the vblank
3749 interrupt after mode setting, since on many devices the vertical
3750 blank counter is reset to 0 at some point during modeset. Modern
3751 drivers should not call this any more since with kernel mode
3752 setting it is a no-op.
3762 <part id="drmDrivers">
3763 <title>DRM Drivers</title>
3767 This second part of the DRM Developer's Guide documents driver code,
3768 implementation details and also all the driver-specific userspace
3769 interfaces. Especially since all hardware-acceleration interfaces to
3770 userspace are driver specific for efficiency and other reasons these
3771 interfaces can be rather substantial. Hence every driver has its own
3776 <chapter id="drmI915">
3777 <title>drm/i915 Intel GFX Driver</title>
3779 The drm/i915 driver supports all (with the exception of some very early
3780 models) integrated GFX chipsets with both Intel display and rendering
3781 blocks. This excludes a set of SoC platforms with an SGX rendering unit,
3782 those have basic support through the gma500 drm driver.
3785 <title>Display Hardware Handling</title>
3787 This section covers everything related to the display hardware including
3788 the mode setting infrastructure, plane, sprite and cursor handling and
3789 display, output probing and related topics.
3792 <title>Mode Setting Infrastructure</title>
3794 The i915 driver is thus far the only DRM driver which doesn't use the
3795 common DRM helper code to implement mode setting sequences. Thus it
3796 has its own tailor-made infrastructure for executing a display
3797 configuration change.
3801 <title>Plane Configuration</title>
3803 This section covers plane configuration and composition with the
3804 primary plane, sprites, cursors and overlays. This includes the
3805 infrastructure to do atomic vsync'ed updates of all this state and
3806 also tightly coupled topics like watermark setup and computation,
3807 framebuffer compression and panel self refresh.
3811 <title>Output Probing</title>
3813 This section covers output probing and related infrastructure like the
3814 hotplug interrupt storm detection and mitigation code. Note that the
3815 i915 driver still uses most of the common DRM helper code for output
3816 probing, so those sections fully apply.
3821 !Pdrivers/gpu/drm/i915/i915_reg.h DPIO
3823 <title>Dual channel PHY (VLV/CHV)</title>
3825 <colspec colname="c0" />
3826 <colspec colname="c1" />
3827 <colspec colname="c2" />
3828 <colspec colname="c3" />
3829 <colspec colname="c4" />
3830 <colspec colname="c5" />
3831 <colspec colname="c6" />
3832 <colspec colname="c7" />
3833 <spanspec spanname="ch0" namest="c0" nameend="c3" />
3834 <spanspec spanname="ch1" namest="c4" nameend="c7" />
3835 <spanspec spanname="ch0pcs01" namest="c0" nameend="c1" />
3836 <spanspec spanname="ch0pcs23" namest="c2" nameend="c3" />
3837 <spanspec spanname="ch1pcs01" namest="c4" nameend="c5" />
3838 <spanspec spanname="ch1pcs23" namest="c6" nameend="c7" />
3841 <entry spanname="ch0">CH0</entry>
3842 <entry spanname="ch1">CH1</entry>
3845 <tbody valign="top" align="center">
3847 <entry spanname="ch0">CMN/PLL/REF</entry>
3848 <entry spanname="ch1">CMN/PLL/REF</entry>
3851 <entry spanname="ch0pcs01">PCS01</entry>
3852 <entry spanname="ch0pcs23">PCS23</entry>
3853 <entry spanname="ch1pcs01">PCS01</entry>
3854 <entry spanname="ch1pcs23">PCS23</entry>
3867 <entry spanname="ch0">DDI0</entry>
3868 <entry spanname="ch1">DDI1</entry>
3874 <title>Single channel PHY (CHV)</title>
3876 <colspec colname="c0" />
3877 <colspec colname="c1" />
3878 <colspec colname="c2" />
3879 <colspec colname="c3" />
3880 <spanspec spanname="ch0" namest="c0" nameend="c3" />
3881 <spanspec spanname="ch0pcs01" namest="c0" nameend="c1" />
3882 <spanspec spanname="ch0pcs23" namest="c2" nameend="c3" />
3885 <entry spanname="ch0">CH0</entry>
3888 <tbody valign="top" align="center">
3890 <entry spanname="ch0">CMN/PLL/REF</entry>
3893 <entry spanname="ch0pcs01">PCS01</entry>
3894 <entry spanname="ch0pcs23">PCS23</entry>
3903 <entry spanname="ch0">DDI2</entry>
3912 <title>Memory Management and Command Submission</title>
3914 This sections covers all things related to the GEM implementation in the
3918 <title>Batchbuffer Parsing</title>
3919 !Pdrivers/gpu/drm/i915/i915_cmd_parser.c batch buffer command parser
3920 !Idrivers/gpu/drm/i915/i915_cmd_parser.c
3923 <title>Logical Rings, Logical Ring Contexts and Execlists</title>
3924 !Pdrivers/gpu/drm/i915/intel_lrc.c Logical Rings, Logical Ring Contexts and Execlists
3925 !Idrivers/gpu/drm/i915/intel_lrc.c
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