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>
35 <year>2008-2009</year>
37 <holder>Intel Corporation</holder>
38 <holder>Laurent Pinchart</holder>
43 The contents of this file may be used under the terms of the GNU
44 General Public License version 2 (the "GPL") as distributed in
45 the kernel source COPYING file.
50 <!-- Put document revisions here, newest first. -->
52 <revnumber>1.0</revnumber>
53 <date>2012-07-13</date>
54 <authorinitials>LP</authorinitials>
55 <revremark>Added extensive documentation about driver internals.
65 <chapter id="drmIntroduction">
66 <title>Introduction</title>
68 The Linux DRM layer contains code intended to support the needs
69 of complex graphics devices, usually containing programmable
70 pipelines well suited to 3D graphics acceleration. Graphics
71 drivers in the kernel may make use of DRM functions to make
72 tasks like memory management, interrupt handling and DMA easier,
73 and provide a uniform interface to applications.
76 A note on versions: this guide covers features found in the DRM
77 tree, including the TTM memory manager, output configuration and
78 mode setting, and the new vblank internals, in addition to all
79 the regular features found in current kernels.
82 [Insert diagram of typical DRM stack here]
88 <chapter id="drmInternals">
89 <title>DRM Internals</title>
91 This chapter documents DRM internals relevant to driver authors
92 and developers working to add support for the latest features to
96 First, we go over some typical driver initialization
97 requirements, like setting up command buffers, creating an
98 initial output configuration, and initializing core services.
99 Subsequent sections cover core internals in more detail,
100 providing implementation notes and examples.
103 The DRM layer provides several services to graphics drivers,
104 many of them driven by the application interfaces it provides
105 through libdrm, the library that wraps most of the DRM ioctls.
106 These include vblank event handling, memory
107 management, output management, framebuffer management, command
108 submission & fencing, suspend/resume support, and DMA
112 <!-- Internals: driver init -->
115 <title>Driver Initialization</title>
117 At the core of every DRM driver is a <structname>drm_driver</structname>
118 structure. Drivers typically statically initialize a drm_driver structure,
119 and then pass it to one of the <function>drm_*_init()</function> functions
120 to register it with the DRM subsystem.
123 The <structname>drm_driver</structname> structure contains static
124 information that describes the driver and features it supports, and
125 pointers to methods that the DRM core will call to implement the DRM API.
126 We will first go through the <structname>drm_driver</structname> static
127 information fields, and will then describe individual operations in
128 details as they get used in later sections.
131 <title>Driver Information</title>
133 <title>Driver Features</title>
135 Drivers inform the DRM core about their requirements and supported
136 features by setting appropriate flags in the
137 <structfield>driver_features</structfield> field. Since those flags
138 influence the DRM core behaviour since registration time, most of them
139 must be set to registering the <structname>drm_driver</structname>
142 <synopsis>u32 driver_features;</synopsis>
144 <title>Driver Feature Flags</title>
146 <term>DRIVER_USE_AGP</term>
148 Driver uses AGP interface, the DRM core will manage AGP resources.
152 <term>DRIVER_REQUIRE_AGP</term>
154 Driver needs AGP interface to function. AGP initialization failure
155 will become a fatal error.
159 <term>DRIVER_USE_MTRR</term>
161 Driver uses MTRR interface for mapping memory, the DRM core will
162 manage MTRR resources. Deprecated.
166 <term>DRIVER_PCI_DMA</term>
168 Driver is capable of PCI DMA, mapping of PCI DMA buffers to
169 userspace will be enabled. Deprecated.
173 <term>DRIVER_SG</term>
175 Driver can perform scatter/gather DMA, allocation and mapping of
176 scatter/gather buffers will be enabled. Deprecated.
180 <term>DRIVER_HAVE_DMA</term>
182 Driver supports DMA, the userspace DMA API will be supported.
187 <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
189 DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler. The
190 DRM core will automatically register an interrupt handler when the
191 flag is set. DRIVER_IRQ_SHARED indicates whether the device &
192 handler support shared IRQs (note that this is required of PCI
197 <term>DRIVER_IRQ_VBL</term>
198 <listitem><para>Unused. Deprecated.</para></listitem>
201 <term>DRIVER_DMA_QUEUE</term>
203 Should be set if the driver queues DMA requests and completes them
204 asynchronously. Deprecated.
208 <term>DRIVER_FB_DMA</term>
210 Driver supports DMA to/from the framebuffer, mapping of frambuffer
211 DMA buffers to userspace will be supported. Deprecated.
215 <term>DRIVER_IRQ_VBL2</term>
216 <listitem><para>Unused. Deprecated.</para></listitem>
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.
239 <title>Major, Minor and Patchlevel</title>
242 int patchlevel;</synopsis>
244 The DRM core identifies driver versions by a major, minor and patch
245 level triplet. The information is printed to the kernel log at
246 initialization time and passed to userspace through the
247 DRM_IOCTL_VERSION ioctl.
250 The major and minor numbers are also used to verify the requested driver
251 API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
252 between minor versions, applications can call DRM_IOCTL_SET_VERSION to
253 select a specific version of the API. If the requested major isn't equal
254 to the driver major, or the requested minor is larger than the driver
255 minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
256 the driver's set_version() method will be called with the requested
261 <title>Name, Description and Date</title>
262 <synopsis>char *name;
264 char *date;</synopsis>
266 The driver name is printed to the kernel log at initialization time,
267 used for IRQ registration and passed to userspace through
271 The driver description is a purely informative string passed to
272 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
276 The driver date, formatted as YYYYMMDD, is meant to identify the date of
277 the latest modification to the driver. However, as most drivers fail to
278 update it, its value is mostly useless. The DRM core prints it to the
279 kernel log at initialization time and passes it to userspace through the
280 DRM_IOCTL_VERSION ioctl.
285 <title>Driver Load</title>
287 The <methodname>load</methodname> method is the driver and device
288 initialization entry point. The method is responsible for allocating and
289 initializing driver private data, specifying supported performance
290 counters, performing resource allocation and mapping (e.g. acquiring
291 clocks, mapping registers or allocating command buffers), initializing
292 the memory manager (<xref linkend="drm-memory-management"/>), installing
293 the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
294 vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
295 setting (<xref linkend="drm-mode-setting"/>) and initial output
296 configuration (<xref linkend="drm-kms-init"/>).
299 If compatibility is a concern (e.g. with drivers converted over from
300 User Mode Setting to Kernel Mode Setting), care must be taken to prevent
301 device initialization and control that is incompatible with currently
302 active userspace drivers. For instance, if user level mode setting
303 drivers are in use, it would be problematic to perform output discovery
304 & configuration at load time. Likewise, if user-level drivers
305 unaware of memory management are in use, memory management and command
306 buffer setup may need to be omitted. These requirements are
307 driver-specific, and care needs to be taken to keep both old and new
308 applications and libraries working.
310 <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
312 The method takes two arguments, a pointer to the newly created
313 <structname>drm_device</structname> and flags. The flags are used to
314 pass the <structfield>driver_data</structfield> field of the device id
315 corresponding to the device passed to <function>drm_*_init()</function>.
316 Only PCI devices currently use this, USB and platform DRM drivers have
317 their <methodname>load</methodname> method called with flags to 0.
320 <title>Driver Private & Performance Counters</title>
322 The driver private hangs off the main
323 <structname>drm_device</structname> structure and can be used for
324 tracking various device-specific bits of information, like register
325 offsets, command buffer status, register state for suspend/resume, etc.
326 At load time, a driver may simply allocate one and set
327 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
328 appropriately; it should be freed and
329 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
330 set to NULL when the driver is unloaded.
333 DRM supports several counters which were used for rough performance
334 characterization. This stat counter system is deprecated and should not
335 be used. If performance monitoring is desired, the developer should
336 investigate and potentially enhance the kernel perf and tracing
337 infrastructure to export GPU related performance information for
338 consumption by performance monitoring tools and applications.
341 <sect3 id="drm-irq-registration">
342 <title>IRQ Registration</title>
344 The DRM core tries to facilitate IRQ handler registration and
345 unregistration by providing <function>drm_irq_install</function> and
346 <function>drm_irq_uninstall</function> functions. Those functions only
347 support a single interrupt per device.
349 <!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
351 Both functions get the device IRQ by calling
352 <function>drm_dev_to_irq</function>. This inline function will call a
353 bus-specific operation to retrieve the IRQ number. For platform devices,
354 <function>platform_get_irq</function>(..., 0) is used to retrieve the
358 <function>drm_irq_install</function> starts by calling the
359 <methodname>irq_preinstall</methodname> driver operation. The operation
360 is optional and must make sure that the interrupt will not get fired by
361 clearing all pending interrupt flags or disabling the interrupt.
364 The IRQ will then be requested by a call to
365 <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
366 feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
370 The IRQ handler function must be provided as the mandatory irq_handler
371 driver operation. It will get passed directly to
372 <function>request_irq</function> and thus has the same prototype as all
373 IRQ handlers. It will get called with a pointer to the DRM device as the
377 Finally the function calls the optional
378 <methodname>irq_postinstall</methodname> driver operation. The operation
379 usually enables interrupts (excluding the vblank interrupt, which is
380 enabled separately), but drivers may choose to enable/disable interrupts
384 <function>drm_irq_uninstall</function> is similarly used to uninstall an
385 IRQ handler. It starts by waking up all processes waiting on a vblank
386 interrupt to make sure they don't hang, and then calls the optional
387 <methodname>irq_uninstall</methodname> driver operation. The operation
388 must disable all hardware interrupts. Finally the function frees the IRQ
389 by calling <function>free_irq</function>.
393 <title>Memory Manager Initialization</title>
395 Every DRM driver requires a memory manager which must be initialized at
396 load time. DRM currently contains two memory managers, the Translation
397 Table Manager (TTM) and the Graphics Execution Manager (GEM).
398 This document describes the use of the GEM memory manager only. See
399 <xref linkend="drm-memory-management"/> for details.
403 <title>Miscellaneous Device Configuration</title>
405 Another task that may be necessary for PCI devices during configuration
406 is mapping the video BIOS. On many devices, the VBIOS describes device
407 configuration, LCD panel timings (if any), and contains flags indicating
408 device state. Mapping the BIOS can be done using the pci_map_rom() call,
409 a convenience function that takes care of mapping the actual ROM,
410 whether it has been shadowed into memory (typically at address 0xc0000)
411 or exists on the PCI device in the ROM BAR. Note that after the ROM has
412 been mapped and any necessary information has been extracted, it should
413 be unmapped; on many devices, the ROM address decoder is shared with
414 other BARs, so leaving it mapped could cause undesired behaviour like
415 hangs or memory corruption.
416 <!--!Fdrivers/pci/rom.c pci_map_rom-->
422 <!-- Internals: memory management -->
424 <sect1 id="drm-memory-management">
425 <title>Memory management</title>
427 Modern Linux systems require large amount of graphics memory to store
428 frame buffers, textures, vertices and other graphics-related data. Given
429 the very dynamic nature of many of that data, managing graphics memory
430 efficiently is thus crucial for the graphics stack and plays a central
431 role in the DRM infrastructure.
434 The DRM core includes two memory managers, namely Translation Table Maps
435 (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
436 manager to be developed and tried to be a one-size-fits-them all
437 solution. It provides a single userspace API to accomodate the need of
438 all hardware, supporting both Unified Memory Architecture (UMA) devices
439 and devices with dedicated video RAM (i.e. most discrete video cards).
440 This resulted in a large, complex piece of code that turned out to be
441 hard to use for driver development.
444 GEM started as an Intel-sponsored project in reaction to TTM's
445 complexity. Its design philosophy is completely different: instead of
446 providing a solution to every graphics memory-related problems, GEM
447 identified common code between drivers and created a support library to
448 share it. GEM has simpler initialization and execution requirements than
449 TTM, but has no video RAM management capabitilies and is thus limited to
453 <title>The Translation Table Manager (TTM)</title>
455 TTM design background and information belongs here.
458 <title>TTM initialization</title>
459 <warning><para>This section is outdated.</para></warning>
461 Drivers wishing to support TTM must fill out a drm_bo_driver
462 structure. The structure contains several fields with function
463 pointers for initializing the TTM, allocating and freeing memory,
464 waiting for command completion and fence synchronization, and memory
465 migration. See the radeon_ttm.c file for an example of usage.
468 The ttm_global_reference structure is made up of several fields:
471 struct ttm_global_reference {
472 enum ttm_global_types global_type;
475 int (*init) (struct ttm_global_reference *);
476 void (*release) (struct ttm_global_reference *);
480 There should be one global reference structure for your memory
481 manager as a whole, and there will be others for each object
482 created by the memory manager at runtime. Your global TTM should
483 have a type of TTM_GLOBAL_TTM_MEM. The size field for the global
484 object should be sizeof(struct ttm_mem_global), and the init and
485 release hooks should point at your driver-specific init and
486 release routines, which probably eventually call
487 ttm_mem_global_init and ttm_mem_global_release, respectively.
490 Once your global TTM accounting structure is set up and initialized
491 by calling ttm_global_item_ref() on it,
492 you need to create a buffer object TTM to
493 provide a pool for buffer object allocation by clients and the
494 kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO,
495 and its size should be sizeof(struct ttm_bo_global). Again,
496 driver-specific init and release functions may be provided,
497 likely eventually calling ttm_bo_global_init() and
498 ttm_bo_global_release(), respectively. Also, like the previous
499 object, ttm_global_item_ref() is used to create an initial reference
500 count for the TTM, which will call your initialization function.
505 <title>The Graphics Execution Manager (GEM)</title>
507 The GEM design approach has resulted in a memory manager that doesn't
508 provide full coverage of all (or even all common) use cases in its
509 userspace or kernel API. GEM exposes a set of standard memory-related
510 operations to userspace and a set of helper functions to drivers, and let
511 drivers implement hardware-specific operations with their own private API.
514 The GEM userspace API is described in the
515 <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
516 Execution Manager</citetitle></ulink> article on LWN. While slightly
517 outdated, the document provides a good overview of the GEM API principles.
518 Buffer allocation and read and write operations, described as part of the
519 common GEM API, are currently implemented using driver-specific ioctls.
522 GEM is data-agnostic. It manages abstract buffer objects without knowing
523 what individual buffers contain. APIs that require knowledge of buffer
524 contents or purpose, such as buffer allocation or synchronization
525 primitives, are thus outside of the scope of GEM and must be implemented
526 using driver-specific ioctls.
529 On a fundamental level, GEM involves several operations:
531 <listitem>Memory allocation and freeing</listitem>
532 <listitem>Command execution</listitem>
533 <listitem>Aperture management at command execution time</listitem>
535 Buffer object allocation is relatively straightforward and largely
536 provided by Linux's shmem layer, which provides memory to back each
540 Device-specific operations, such as command execution, pinning, buffer
541 read & write, mapping, and domain ownership transfers are left to
542 driver-specific ioctls.
545 <title>GEM Initialization</title>
547 Drivers that use GEM must set the DRIVER_GEM bit in the struct
548 <structname>drm_driver</structname>
549 <structfield>driver_features</structfield> field. The DRM core will
550 then automatically initialize the GEM core before calling the
551 <methodname>load</methodname> operation. Behind the scene, this will
552 create a DRM Memory Manager object which provides an address space
553 pool for object allocation.
556 In a KMS configuration, drivers need to allocate and initialize a
557 command ring buffer following core GEM initialization if required by
558 the hardware. UMA devices usually have what is called a "stolen"
559 memory region, which provides space for the initial framebuffer and
560 large, contiguous memory regions required by the device. This space is
561 typically not managed by GEM, and must be initialized separately into
562 its own DRM MM object.
566 <title>GEM Objects Creation</title>
568 GEM splits creation of GEM objects and allocation of the memory that
569 backs them in two distinct operations.
572 GEM objects are represented by an instance of struct
573 <structname>drm_gem_object</structname>. Drivers usually need to extend
574 GEM objects with private information and thus create a driver-specific
575 GEM object structure type that embeds an instance of struct
576 <structname>drm_gem_object</structname>.
579 To create a GEM object, a driver allocates memory for an instance of its
580 specific GEM object type and initializes the embedded struct
581 <structname>drm_gem_object</structname> with a call to
582 <function>drm_gem_object_init</function>. The function takes a pointer to
583 the DRM device, a pointer to the GEM object and the buffer object size
587 GEM uses shmem to allocate anonymous pageable memory.
588 <function>drm_gem_object_init</function> will create an shmfs file of
589 the requested size and store it into the struct
590 <structname>drm_gem_object</structname> <structfield>filp</structfield>
591 field. The memory is used as either main storage for the object when the
592 graphics hardware uses system memory directly or as a backing store
596 Drivers are responsible for the actual physical pages allocation by
597 calling <function>shmem_read_mapping_page_gfp</function> for each page.
598 Note that they can decide to allocate pages when initializing the GEM
599 object, or to delay allocation until the memory is needed (for instance
600 when a page fault occurs as a result of a userspace memory access or
601 when the driver needs to start a DMA transfer involving the memory).
604 Anonymous pageable memory allocation is not always desired, for instance
605 when the hardware requires physically contiguous system memory as is
606 often the case in embedded devices. Drivers can create GEM objects with
607 no shmfs backing (called private GEM objects) by initializing them with
608 a call to <function>drm_gem_private_object_init</function> instead of
609 <function>drm_gem_object_init</function>. Storage for private GEM
610 objects must be managed by drivers.
613 Drivers that do not need to extend GEM objects with private information
614 can call the <function>drm_gem_object_alloc</function> function to
615 allocate and initialize a struct <structname>drm_gem_object</structname>
616 instance. The GEM core will call the optional driver
617 <methodname>gem_init_object</methodname> operation after initializing
618 the GEM object with <function>drm_gem_object_init</function>.
619 <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
622 No alloc-and-init function exists for private GEM objects.
626 <title>GEM Objects Lifetime</title>
628 All GEM objects are reference-counted by the GEM core. References can be
629 acquired and release by <function>calling drm_gem_object_reference</function>
630 and <function>drm_gem_object_unreference</function> respectively. The
631 caller must hold the <structname>drm_device</structname>
632 <structfield>struct_mutex</structfield> lock. As a convenience, GEM
633 provides the <function>drm_gem_object_reference_unlocked</function> and
634 <function>drm_gem_object_unreference_unlocked</function> functions that
635 can be called without holding the lock.
638 When the last reference to a GEM object is released the GEM core calls
639 the <structname>drm_driver</structname>
640 <methodname>gem_free_object</methodname> operation. That operation is
641 mandatory for GEM-enabled drivers and must free the GEM object and all
642 associated resources.
645 <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
646 Drivers are responsible for freeing all GEM object resources, including
647 the resources created by the GEM core. If an mmap offset has been
648 created for the object (in which case
649 <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
650 is not NULL) it must be freed by a call to
651 <function>drm_gem_free_mmap_offset</function>. The shmfs backing store
652 must be released by calling <function>drm_gem_object_release</function>
653 (that function can safely be called if no shmfs backing store has been
658 <title>GEM Objects Naming</title>
660 Communication between userspace and the kernel refers to GEM objects
661 using local handles, global names or, more recently, file descriptors.
662 All of those are 32-bit integer values; the usual Linux kernel limits
663 apply to the file descriptors.
666 GEM handles are local to a DRM file. Applications get a handle to a GEM
667 object through a driver-specific ioctl, and can use that handle to refer
668 to the GEM object in other standard or driver-specific ioctls. Closing a
669 DRM file handle frees all its GEM handles and dereferences the
670 associated GEM objects.
673 To create a handle for a GEM object drivers call
674 <function>drm_gem_handle_create</function>. The function takes a pointer
675 to the DRM file and the GEM object and returns a locally unique handle.
676 When the handle is no longer needed drivers delete it with a call to
677 <function>drm_gem_handle_delete</function>. Finally the GEM object
678 associated with a handle can be retrieved by a call to
679 <function>drm_gem_object_lookup</function>.
682 Handles don't take ownership of GEM objects, they only take a reference
683 to the object that will be dropped when the handle is destroyed. To
684 avoid leaking GEM objects, drivers must make sure they drop the
685 reference(s) they own (such as the initial reference taken at object
686 creation time) as appropriate, without any special consideration for the
687 handle. For example, in the particular case of combined GEM object and
688 handle creation in the implementation of the
689 <methodname>dumb_create</methodname> operation, drivers must drop the
690 initial reference to the GEM object before returning the handle.
693 GEM names are similar in purpose to handles but are not local to DRM
694 files. They can be passed between processes to reference a GEM object
695 globally. Names can't be used directly to refer to objects in the DRM
696 API, applications must convert handles to names and names to handles
697 using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
698 respectively. The conversion is handled by the DRM core without any
699 driver-specific support.
702 Similar to global names, GEM file descriptors are also used to share GEM
703 objects across processes. They offer additional security: as file
704 descriptors must be explictly sent over UNIX domain sockets to be shared
705 between applications, they can't be guessed like the globally unique GEM
709 Drivers that support GEM file descriptors, also known as the DRM PRIME
710 API, must set the DRIVER_PRIME bit in the struct
711 <structname>drm_driver</structname>
712 <structfield>driver_features</structfield> field, and implement the
713 <methodname>prime_handle_to_fd</methodname> and
714 <methodname>prime_fd_to_handle</methodname> operations.
717 <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
718 struct drm_file *file_priv, uint32_t handle,
719 uint32_t flags, int *prime_fd);
720 int (*prime_fd_to_handle)(struct drm_device *dev,
721 struct drm_file *file_priv, int prime_fd,
722 uint32_t *handle);</synopsis>
723 Those two operations convert a handle to a PRIME file descriptor and
724 vice versa. Drivers must use the kernel dma-buf buffer sharing framework
725 to manage the PRIME file descriptors.
728 While non-GEM drivers must implement the operations themselves, GEM
729 drivers must use the <function>drm_gem_prime_handle_to_fd</function>
730 and <function>drm_gem_prime_fd_to_handle</function> helper functions.
731 Those helpers rely on the driver
732 <methodname>gem_prime_export</methodname> and
733 <methodname>gem_prime_import</methodname> operations to create a dma-buf
734 instance from a GEM object (dma-buf exporter role) and to create a GEM
735 object from a dma-buf instance (dma-buf importer role).
738 <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
739 struct drm_gem_object *obj,
741 struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
742 struct dma_buf *dma_buf);</synopsis>
743 These two operations are mandatory for GEM drivers that support DRM
747 <sect3 id="drm-gem-objects-mapping">
748 <title>GEM Objects Mapping</title>
750 Because mapping operations are fairly heavyweight GEM favours
751 read/write-like access to buffers, implemented through driver-specific
752 ioctls, over mapping buffers to userspace. However, when random access
753 to the buffer is needed (to perform software rendering for instance),
754 direct access to the object can be more efficient.
757 The mmap system call can't be used directly to map GEM objects, as they
758 don't have their own file handle. Two alternative methods currently
759 co-exist to map GEM objects to userspace. The first method uses a
760 driver-specific ioctl to perform the mapping operation, calling
761 <function>do_mmap</function> under the hood. This is often considered
762 dubious, seems to be discouraged for new GEM-enabled drivers, and will
763 thus not be described here.
766 The second method uses the mmap system call on the DRM file handle.
767 <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
768 off_t offset);</synopsis>
769 DRM identifies the GEM object to be mapped by a fake offset passed
770 through the mmap offset argument. Prior to being mapped, a GEM object
771 must thus be associated with a fake offset. To do so, drivers must call
772 <function>drm_gem_create_mmap_offset</function> on the object. The
773 function allocates a fake offset range from a pool and stores the
774 offset divided by PAGE_SIZE in
775 <literal>obj->map_list.hash.key</literal>. Care must be taken not to
776 call <function>drm_gem_create_mmap_offset</function> if a fake offset
777 has already been allocated for the object. This can be tested by
778 <literal>obj->map_list.map</literal> being non-NULL.
781 Once allocated, the fake offset value
782 (<literal>obj->map_list.hash.key << PAGE_SHIFT</literal>)
783 must be passed to the application in a driver-specific way and can then
784 be used as the mmap offset argument.
787 The GEM core provides a helper method <function>drm_gem_mmap</function>
788 to handle object mapping. The method can be set directly as the mmap
789 file operation handler. It will look up the GEM object based on the
790 offset value and set the VMA operations to the
791 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
792 field. Note that <function>drm_gem_mmap</function> doesn't map memory to
793 userspace, but relies on the driver-provided fault handler to map pages
797 To use <function>drm_gem_mmap</function>, drivers must fill the struct
798 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
799 field with a pointer to VM operations.
802 <synopsis>struct vm_operations_struct *gem_vm_ops
804 struct vm_operations_struct {
805 void (*open)(struct vm_area_struct * area);
806 void (*close)(struct vm_area_struct * area);
807 int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
811 The <methodname>open</methodname> and <methodname>close</methodname>
812 operations must update the GEM object reference count. Drivers can use
813 the <function>drm_gem_vm_open</function> and
814 <function>drm_gem_vm_close</function> helper functions directly as open
818 The fault operation handler is responsible for mapping individual pages
819 to userspace when a page fault occurs. Depending on the memory
820 allocation scheme, drivers can allocate pages at fault time, or can
821 decide to allocate memory for the GEM object at the time the object is
825 Drivers that want to map the GEM object upfront instead of handling page
826 faults can implement their own mmap file operation handler.
830 <title>Dumb GEM Objects</title>
832 The GEM API doesn't standardize GEM objects creation and leaves it to
833 driver-specific ioctls. While not an issue for full-fledged graphics
834 stacks that include device-specific userspace components (in libdrm for
835 instance), this limit makes DRM-based early boot graphics unnecessarily
839 Dumb GEM objects partly alleviate the problem by providing a standard
840 API to create dumb buffers suitable for scanout, which can then be used
841 to create KMS frame buffers.
844 To support dumb GEM objects drivers must implement the
845 <methodname>dumb_create</methodname>,
846 <methodname>dumb_destroy</methodname> and
847 <methodname>dumb_map_offset</methodname> operations.
851 <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
852 struct drm_mode_create_dumb *args);</synopsis>
854 The <methodname>dumb_create</methodname> operation creates a GEM
855 object suitable for scanout based on the width, height and depth
856 from the struct <structname>drm_mode_create_dumb</structname>
857 argument. It fills the argument's <structfield>handle</structfield>,
858 <structfield>pitch</structfield> and <structfield>size</structfield>
859 fields with a handle for the newly created GEM object and its line
860 pitch and size in bytes.
864 <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
865 uint32_t handle);</synopsis>
867 The <methodname>dumb_destroy</methodname> operation destroys a dumb
868 GEM object created by <methodname>dumb_create</methodname>.
872 <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
873 uint32_t handle, uint64_t *offset);</synopsis>
875 The <methodname>dumb_map_offset</methodname> operation associates an
876 mmap fake offset with the GEM object given by the handle and returns
877 it. Drivers must use the
878 <function>drm_gem_create_mmap_offset</function> function to
879 associate the fake offset as described in
880 <xref linkend="drm-gem-objects-mapping"/>.
886 <title>Memory Coherency</title>
888 When mapped to the device or used in a command buffer, backing pages
889 for an object are flushed to memory and marked write combined so as to
890 be coherent with the GPU. Likewise, if the CPU accesses an object
891 after the GPU has finished rendering to the object, then the object
892 must be made coherent with the CPU's view of memory, usually involving
893 GPU cache flushing of various kinds. This core CPU<->GPU
894 coherency management is provided by a device-specific ioctl, which
895 evaluates an object's current domain and performs any necessary
896 flushing or synchronization to put the object into the desired
897 coherency domain (note that the object may be busy, i.e. an active
898 render target; in that case, setting the domain blocks the client and
899 waits for rendering to complete before performing any necessary
900 flushing operations).
904 <title>Command Execution</title>
906 Perhaps the most important GEM function for GPU devices is providing a
907 command execution interface to clients. Client programs construct
908 command buffers containing references to previously allocated memory
909 objects, and then submit them to GEM. At that point, GEM takes care to
910 bind all the objects into the GTT, execute the buffer, and provide
911 necessary synchronization between clients accessing the same buffers.
912 This often involves evicting some objects from the GTT and re-binding
913 others (a fairly expensive operation), and providing relocation
914 support which hides fixed GTT offsets from clients. Clients must take
915 care not to submit command buffers that reference more objects than
916 can fit in the GTT; otherwise, GEM will reject them and no rendering
917 will occur. Similarly, if several objects in the buffer require fence
918 registers to be allocated for correct rendering (e.g. 2D blits on
919 pre-965 chips), care must be taken not to require more fence registers
920 than are available to the client. Such resource management should be
921 abstracted from the client in libdrm.
927 <!-- Internals: mode setting -->
929 <sect1 id="drm-mode-setting">
930 <title>Mode Setting</title>
932 Drivers must initialize the mode setting core by calling
933 <function>drm_mode_config_init</function> on the DRM device. The function
934 initializes the <structname>drm_device</structname>
935 <structfield>mode_config</structfield> field and never fails. Once done,
936 mode configuration must be setup by initializing the following fields.
940 <synopsis>int min_width, min_height;
941 int max_width, max_height;</synopsis>
943 Minimum and maximum width and height of the frame buffers in pixel
948 <synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
949 <para>Mode setting functions.</para>
953 <title>Frame Buffer Creation</title>
954 <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
955 struct drm_file *file_priv,
956 struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
958 Frame buffers are abstract memory objects that provide a source of
959 pixels to scanout to a CRTC. Applications explicitly request the
960 creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
961 receive an opaque handle that can be passed to the KMS CRTC control,
962 plane configuration and page flip functions.
965 Frame buffers rely on the underneath memory manager for low-level memory
966 operations. When creating a frame buffer applications pass a memory
967 handle (or a list of memory handles for multi-planar formats) through
968 the <parameter>drm_mode_fb_cmd2</parameter> argument. This document
969 assumes that the driver uses GEM, those handles thus reference GEM
973 Drivers must first validate the requested frame buffer parameters passed
974 through the mode_cmd argument. In particular this is where invalid
975 sizes, pixel formats or pitches can be caught.
978 If the parameters are deemed valid, drivers then create, initialize and
979 return an instance of struct <structname>drm_framebuffer</structname>.
980 If desired the instance can be embedded in a larger driver-specific
981 structure. The new instance is initialized with a call to
982 <function>drm_framebuffer_init</function> which takes a pointer to DRM
983 frame buffer operations (struct
984 <structname>drm_framebuffer_funcs</structname>). Frame buffer operations are
987 <synopsis>int (*create_handle)(struct drm_framebuffer *fb,
988 struct drm_file *file_priv, unsigned int *handle);</synopsis>
990 Create a handle to the frame buffer underlying memory object. If
991 the frame buffer uses a multi-plane format, the handle will
992 reference the memory object associated with the first plane.
995 Drivers call <function>drm_gem_handle_create</function> to create
1000 <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
1002 Destroy the frame buffer object and frees all associated
1003 resources. Drivers must call
1004 <function>drm_framebuffer_cleanup</function> to free resources
1005 allocated by the DRM core for the frame buffer object, and must
1006 make sure to unreference all memory objects associated with the
1007 frame buffer. Handles created by the
1008 <methodname>create_handle</methodname> operation are released by
1013 <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
1014 struct drm_file *file_priv, unsigned flags, unsigned color,
1015 struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
1017 This optional operation notifies the driver that a region of the
1018 frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
1025 After initializing the <structname>drm_framebuffer</structname>
1026 instance drivers must fill its <structfield>width</structfield>,
1027 <structfield>height</structfield>, <structfield>pitches</structfield>,
1028 <structfield>offsets</structfield>, <structfield>depth</structfield>,
1029 <structfield>bits_per_pixel</structfield> and
1030 <structfield>pixel_format</structfield> fields from the values passed
1031 through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
1032 should call the <function>drm_helper_mode_fill_fb_struct</function>
1033 helper function to do so.
1037 <title>Output Polling</title>
1038 <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
1040 This operation notifies the driver that the status of one or more
1041 connectors has changed. Drivers that use the fb helper can just call the
1042 <function>drm_fb_helper_hotplug_event</function> function to handle this
1048 <!-- Internals: kms initialization and cleanup -->
1050 <sect1 id="drm-kms-init">
1051 <title>KMS Initialization and Cleanup</title>
1053 A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
1054 and connectors. KMS drivers must thus create and initialize all those
1055 objects at load time after initializing mode setting.
1058 <title>CRTCs (struct <structname>drm_crtc</structname>)</title>
1060 A CRTC is an abstraction representing a part of the chip that contains a
1061 pointer to a scanout buffer. Therefore, the number of CRTCs available
1062 determines how many independent scanout buffers can be active at any
1063 given time. The CRTC structure contains several fields to support this:
1064 a pointer to some video memory (abstracted as a frame buffer object), a
1065 display mode, and an (x, y) offset into the video memory to support
1066 panning or configurations where one piece of video memory spans multiple
1070 <title>CRTC Initialization</title>
1072 A KMS device must create and register at least one struct
1073 <structname>drm_crtc</structname> instance. The instance is allocated
1074 and zeroed by the driver, possibly as part of a larger structure, and
1075 registered with a call to <function>drm_crtc_init</function> with a
1076 pointer to CRTC functions.
1080 <title>CRTC Operations</title>
1082 <title>Set Configuration</title>
1083 <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
1085 Apply a new CRTC configuration to the device. The configuration
1086 specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
1087 the frame buffer, a display mode and an array of connectors to drive
1088 with the CRTC if possible.
1091 If the frame buffer specified in the configuration is NULL, the driver
1092 must detach all encoders connected to the CRTC and all connectors
1093 attached to those encoders and disable them.
1096 This operation is called with the mode config lock held.
1099 FIXME: How should set_config interact with DPMS? If the CRTC is
1100 suspended, should it be resumed?
1104 <title>Page Flipping</title>
1105 <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
1106 struct drm_pending_vblank_event *event);</synopsis>
1108 Schedule a page flip to the given frame buffer for the CRTC. This
1109 operation is called with the mode config mutex held.
1112 Page flipping is a synchronization mechanism that replaces the frame
1113 buffer being scanned out by the CRTC with a new frame buffer during
1114 vertical blanking, avoiding tearing. When an application requests a page
1115 flip the DRM core verifies that the new frame buffer is large enough to
1116 be scanned out by the CRTC in the currently configured mode and then
1117 calls the CRTC <methodname>page_flip</methodname> operation with a
1118 pointer to the new frame buffer.
1121 The <methodname>page_flip</methodname> operation schedules a page flip.
1122 Once any pending rendering targetting the new frame buffer has
1123 completed, the CRTC will be reprogrammed to display that frame buffer
1124 after the next vertical refresh. The operation must return immediately
1125 without waiting for rendering or page flip to complete and must block
1126 any new rendering to the frame buffer until the page flip completes.
1129 If a page flip is already pending, the
1130 <methodname>page_flip</methodname> operation must return
1131 -<errorname>EBUSY</errorname>.
1134 To synchronize page flip to vertical blanking the driver will likely
1135 need to enable vertical blanking interrupts. It should call
1136 <function>drm_vblank_get</function> for that purpose, and call
1137 <function>drm_vblank_put</function> after the page flip completes.
1140 If the application has requested to be notified when page flip completes
1141 the <methodname>page_flip</methodname> operation will be called with a
1142 non-NULL <parameter>event</parameter> argument pointing to a
1143 <structname>drm_pending_vblank_event</structname> instance. Upon page
1144 flip completion the driver must call <methodname>drm_send_vblank_event</methodname>
1145 to fill in the event and send to wake up any waiting processes.
1146 This can be performed with
1147 <programlisting><![CDATA[
1148 spin_lock_irqsave(&dev->event_lock, flags);
1150 drm_send_vblank_event(dev, pipe, event);
1151 spin_unlock_irqrestore(&dev->event_lock, flags);
1152 ]]></programlisting>
1155 FIXME: Could drivers that don't need to wait for rendering to complete
1156 just add the event to <literal>dev->vblank_event_list</literal> and
1157 let the DRM core handle everything, as for "normal" vertical blanking
1161 While waiting for the page flip to complete, the
1162 <literal>event->base.link</literal> list head can be used freely by
1163 the driver to store the pending event in a driver-specific list.
1166 If the file handle is closed before the event is signaled, drivers must
1167 take care to destroy the event in their
1168 <methodname>preclose</methodname> operation (and, if needed, call
1169 <function>drm_vblank_put</function>).
1173 <title>Miscellaneous</title>
1176 <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
1177 uint32_t start, uint32_t size);</synopsis>
1179 Apply a gamma table to the device. The operation is optional.
1183 <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
1185 Destroy the CRTC when not needed anymore. See
1186 <xref linkend="drm-kms-init"/>.
1194 <title>Planes (struct <structname>drm_plane</structname>)</title>
1196 A plane represents an image source that can be blended with or overlayed
1197 on top of a CRTC during the scanout process. Planes are associated with
1198 a frame buffer to crop a portion of the image memory (source) and
1199 optionally scale it to a destination size. The result is then blended
1200 with or overlayed on top of a CRTC.
1203 <title>Plane Initialization</title>
1205 Planes are optional. To create a plane, a KMS drivers allocates and
1206 zeroes an instances of struct <structname>drm_plane</structname>
1207 (possibly as part of a larger structure) and registers it with a call
1208 to <function>drm_plane_init</function>. The function takes a bitmask
1209 of the CRTCs that can be associated with the plane, a pointer to the
1210 plane functions and a list of format supported formats.
1214 <title>Plane Operations</title>
1217 <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
1218 struct drm_framebuffer *fb, int crtc_x, int crtc_y,
1219 unsigned int crtc_w, unsigned int crtc_h,
1220 uint32_t src_x, uint32_t src_y,
1221 uint32_t src_w, uint32_t src_h);</synopsis>
1223 Enable and configure the plane to use the given CRTC and frame buffer.
1226 The source rectangle in frame buffer memory coordinates is given by
1227 the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
1228 <parameter>src_w</parameter> and <parameter>src_h</parameter>
1229 parameters (as 16.16 fixed point values). Devices that don't support
1230 subpixel plane coordinates can ignore the fractional part.
1233 The destination rectangle in CRTC coordinates is given by the
1234 <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
1235 <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
1236 parameters (as integer values). Devices scale the source rectangle to
1237 the destination rectangle. If scaling is not supported, and the source
1238 rectangle size doesn't match the destination rectangle size, the
1239 driver must return a -<errorname>EINVAL</errorname> error.
1243 <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
1245 Disable the plane. The DRM core calls this method in response to a
1246 DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
1247 Disabled planes must not be processed by the CRTC.
1251 <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
1253 Destroy the plane when not needed anymore. See
1254 <xref linkend="drm-kms-init"/>.
1261 <title>Encoders (struct <structname>drm_encoder</structname>)</title>
1263 An encoder takes pixel data from a CRTC and converts it to a format
1264 suitable for any attached connectors. On some devices, it may be
1265 possible to have a CRTC send data to more than one encoder. In that
1266 case, both encoders would receive data from the same scanout buffer,
1267 resulting in a "cloned" display configuration across the connectors
1268 attached to each encoder.
1271 <title>Encoder Initialization</title>
1273 As for CRTCs, a KMS driver must create, initialize and register at
1274 least one struct <structname>drm_encoder</structname> instance. The
1275 instance is allocated and zeroed by the driver, possibly as part of a
1279 Drivers must initialize the struct <structname>drm_encoder</structname>
1280 <structfield>possible_crtcs</structfield> and
1281 <structfield>possible_clones</structfield> fields before registering the
1282 encoder. Both fields are bitmasks of respectively the CRTCs that the
1283 encoder can be connected to, and sibling encoders candidate for cloning.
1286 After being initialized, the encoder must be registered with a call to
1287 <function>drm_encoder_init</function>. The function takes a pointer to
1288 the encoder functions and an encoder type. Supported types are
1291 DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
1294 DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
1297 DRM_MODE_ENCODER_LVDS for display panels
1300 DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
1304 DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
1309 Encoders must be attached to a CRTC to be used. DRM drivers leave
1310 encoders unattached at initialization time. Applications (or the fbdev
1311 compatibility layer when implemented) are responsible for attaching the
1312 encoders they want to use to a CRTC.
1316 <title>Encoder Operations</title>
1319 <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
1321 Called to destroy the encoder when not needed anymore. See
1322 <xref linkend="drm-kms-init"/>.
1329 <title>Connectors (struct <structname>drm_connector</structname>)</title>
1331 A connector is the final destination for pixel data on a device, and
1332 usually connects directly to an external display device like a monitor
1333 or laptop panel. A connector can only be attached to one encoder at a
1334 time. The connector is also the structure where information about the
1335 attached display is kept, so it contains fields for display data, EDID
1336 data, DPMS & connection status, and information about modes
1337 supported on the attached displays.
1340 <title>Connector Initialization</title>
1342 Finally a KMS driver must create, initialize, register and attach at
1343 least one struct <structname>drm_connector</structname> instance. The
1344 instance is created as other KMS objects and initialized by setting the
1349 <term><structfield>interlace_allowed</structfield></term>
1351 Whether the connector can handle interlaced modes.
1355 <term><structfield>doublescan_allowed</structfield></term>
1357 Whether the connector can handle doublescan.
1361 <term><structfield>display_info
1362 </structfield></term>
1364 Display information is filled from EDID information when a display
1365 is detected. For non hot-pluggable displays such as flat panels in
1366 embedded systems, the driver should initialize the
1367 <structfield>display_info</structfield>.<structfield>width_mm</structfield>
1369 <structfield>display_info</structfield>.<structfield>height_mm</structfield>
1370 fields with the physical size of the display.
1374 <term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
1376 Connector polling mode, a combination of
1379 <term>DRM_CONNECTOR_POLL_HPD</term>
1381 The connector generates hotplug events and doesn't need to be
1382 periodically polled. The CONNECT and DISCONNECT flags must not
1383 be set together with the HPD flag.
1387 <term>DRM_CONNECTOR_POLL_CONNECT</term>
1389 Periodically poll the connector for connection.
1393 <term>DRM_CONNECTOR_POLL_DISCONNECT</term>
1395 Periodically poll the connector for disconnection.
1399 Set to 0 for connectors that don't support connection status
1405 The connector is then registered with a call to
1406 <function>drm_connector_init</function> with a pointer to the connector
1407 functions and a connector type, and exposed through sysfs with a call to
1408 <function>drm_sysfs_connector_add</function>.
1411 Supported connector types are
1413 <listitem>DRM_MODE_CONNECTOR_VGA</listitem>
1414 <listitem>DRM_MODE_CONNECTOR_DVII</listitem>
1415 <listitem>DRM_MODE_CONNECTOR_DVID</listitem>
1416 <listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
1417 <listitem>DRM_MODE_CONNECTOR_Composite</listitem>
1418 <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
1419 <listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
1420 <listitem>DRM_MODE_CONNECTOR_Component</listitem>
1421 <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
1422 <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
1423 <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
1424 <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
1425 <listitem>DRM_MODE_CONNECTOR_TV</listitem>
1426 <listitem>DRM_MODE_CONNECTOR_eDP</listitem>
1427 <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
1431 Connectors must be attached to an encoder to be used. For devices that
1432 map connectors to encoders 1:1, the connector should be attached at
1433 initialization time with a call to
1434 <function>drm_mode_connector_attach_encoder</function>. The driver must
1435 also set the <structname>drm_connector</structname>
1436 <structfield>encoder</structfield> field to point to the attached
1440 Finally, drivers must initialize the connectors state change detection
1441 with a call to <function>drm_kms_helper_poll_init</function>. If at
1442 least one connector is pollable but can't generate hotplug interrupts
1443 (indicated by the DRM_CONNECTOR_POLL_CONNECT and
1444 DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
1445 automatically be queued to periodically poll for changes. Connectors
1446 that can generate hotplug interrupts must be marked with the
1447 DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
1448 call <function>drm_helper_hpd_irq_event</function>. The function will
1449 queue a delayed work to check the state of all connectors, but no
1450 periodic polling will be done.
1454 <title>Connector Operations</title>
1456 Unless otherwise state, all operations are mandatory.
1460 <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
1462 The DPMS operation sets the power state of a connector. The mode
1465 <listitem><para>DRM_MODE_DPMS_ON</para></listitem>
1466 <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
1467 <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
1468 <listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
1472 In all but DPMS_ON mode the encoder to which the connector is attached
1473 should put the display in low-power mode by driving its signals
1474 appropriately. If more than one connector is attached to the encoder
1475 care should be taken not to change the power state of other displays as
1476 a side effect. Low-power mode should be propagated to the encoders and
1477 CRTCs when all related connectors are put in low-power mode.
1481 <title>Modes</title>
1482 <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
1483 uint32_t max_height);</synopsis>
1485 Fill the mode list with all supported modes for the connector. If the
1486 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1487 arguments are non-zero, the implementation must ignore all modes wider
1488 than <parameter>max_width</parameter> or higher than
1489 <parameter>max_height</parameter>.
1492 The connector must also fill in this operation its
1493 <structfield>display_info</structfield>
1494 <structfield>width_mm</structfield> and
1495 <structfield>height_mm</structfield> fields with the connected display
1496 physical size in millimeters. The fields should be set to 0 if the value
1497 isn't known or is not applicable (for instance for projector devices).
1501 <title>Connection Status</title>
1503 The connection status is updated through polling or hotplug events when
1504 supported (see <xref linkend="drm-kms-connector-polled"/>). The status
1505 value is reported to userspace through ioctls and must not be used
1506 inside the driver, as it only gets initialized by a call to
1507 <function>drm_mode_getconnector</function> from userspace.
1509 <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
1510 bool force);</synopsis>
1512 Check to see if anything is attached to the connector. The
1513 <parameter>force</parameter> parameter is set to false whilst polling or
1514 to true when checking the connector due to user request.
1515 <parameter>force</parameter> can be used by the driver to avoid
1516 expensive, destructive operations during automated probing.
1519 Return connector_status_connected if something is connected to the
1520 connector, connector_status_disconnected if nothing is connected and
1521 connector_status_unknown if the connection state isn't known.
1524 Drivers should only return connector_status_connected if the connection
1525 status has really been probed as connected. Connectors that can't detect
1526 the connection status, or failed connection status probes, should return
1527 connector_status_unknown.
1531 <title>Miscellaneous</title>
1534 <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
1536 Destroy the connector when not needed anymore. See
1537 <xref linkend="drm-kms-init"/>.
1545 <title>Cleanup</title>
1547 The DRM core manages its objects' lifetime. When an object is not needed
1548 anymore the core calls its destroy function, which must clean up and
1549 free every resource allocated for the object. Every
1550 <function>drm_*_init</function> call must be matched with a
1551 corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
1552 (<function>drm_crtc_cleanup</function>), planes
1553 (<function>drm_plane_cleanup</function>), encoders
1554 (<function>drm_encoder_cleanup</function>) and connectors
1555 (<function>drm_connector_cleanup</function>). Furthermore, connectors
1556 that have been added to sysfs must be removed by a call to
1557 <function>drm_sysfs_connector_remove</function> before calling
1558 <function>drm_connector_cleanup</function>.
1561 Connectors state change detection must be cleanup up with a call to
1562 <function>drm_kms_helper_poll_fini</function>.
1566 <title>Output discovery and initialization example</title>
1567 <programlisting><![CDATA[
1568 void intel_crt_init(struct drm_device *dev)
1570 struct drm_connector *connector;
1571 struct intel_output *intel_output;
1573 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
1577 connector = &intel_output->base;
1578 drm_connector_init(dev, &intel_output->base,
1579 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
1581 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
1582 DRM_MODE_ENCODER_DAC);
1584 drm_mode_connector_attach_encoder(&intel_output->base,
1585 &intel_output->enc);
1587 /* Set up the DDC bus. */
1588 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
1589 if (!intel_output->ddc_bus) {
1590 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
1595 intel_output->type = INTEL_OUTPUT_ANALOG;
1596 connector->interlace_allowed = 0;
1597 connector->doublescan_allowed = 0;
1599 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
1600 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
1602 drm_sysfs_connector_add(connector);
1603 }]]></programlisting>
1605 In the example above (taken from the i915 driver), a CRTC, connector and
1606 encoder combination is created. A device-specific i2c bus is also
1607 created for fetching EDID data and performing monitor detection. Once
1608 the process is complete, the new connector is registered with sysfs to
1609 make its properties available to applications.
1614 <!-- Internals: mid-layer helper functions -->
1617 <title>Mid-layer Helper Functions</title>
1619 The CRTC, encoder and connector functions provided by the drivers
1620 implement the DRM API. They're called by the DRM core and ioctl handlers
1621 to handle device state changes and configuration request. As implementing
1622 those functions often requires logic not specific to drivers, mid-layer
1623 helper functions are available to avoid duplicating boilerplate code.
1626 The DRM core contains one mid-layer implementation. The mid-layer provides
1627 implementations of several CRTC, encoder and connector functions (called
1628 from the top of the mid-layer) that pre-process requests and call
1629 lower-level functions provided by the driver (at the bottom of the
1630 mid-layer). For instance, the
1631 <function>drm_crtc_helper_set_config</function> function can be used to
1632 fill the struct <structname>drm_crtc_funcs</structname>
1633 <structfield>set_config</structfield> field. When called, it will split
1634 the <methodname>set_config</methodname> operation in smaller, simpler
1635 operations and call the driver to handle them.
1638 To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
1639 <function>drm_encoder_helper_add</function> and
1640 <function>drm_connector_helper_add</function> functions to install their
1641 mid-layer bottom operations handlers, and fill the
1642 <structname>drm_crtc_funcs</structname>,
1643 <structname>drm_encoder_funcs</structname> and
1644 <structname>drm_connector_funcs</structname> structures with pointers to
1645 the mid-layer top API functions. Installing the mid-layer bottom operation
1646 handlers is best done right after registering the corresponding KMS object.
1649 The mid-layer is not split between CRTC, encoder and connector operations.
1650 To use it, a driver must provide bottom functions for all of the three KMS
1654 <title>Helper Functions</title>
1657 <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
1659 The <function>drm_crtc_helper_set_config</function> helper function
1660 is a CRTC <methodname>set_config</methodname> implementation. It
1661 first tries to locate the best encoder for each connector by calling
1662 the connector <methodname>best_encoder</methodname> helper
1666 After locating the appropriate encoders, the helper function will
1667 call the <methodname>mode_fixup</methodname> encoder and CRTC helper
1668 operations to adjust the requested mode, or reject it completely in
1669 which case an error will be returned to the application. If the new
1670 configuration after mode adjustment is identical to the current
1671 configuration the helper function will return without performing any
1675 If the adjusted mode is identical to the current mode but changes to
1676 the frame buffer need to be applied, the
1677 <function>drm_crtc_helper_set_config</function> function will call
1678 the CRTC <methodname>mode_set_base</methodname> helper operation. If
1679 the adjusted mode differs from the current mode, or if the
1680 <methodname>mode_set_base</methodname> helper operation is not
1681 provided, the helper function performs a full mode set sequence by
1682 calling the <methodname>prepare</methodname>,
1683 <methodname>mode_set</methodname> and
1684 <methodname>commit</methodname> CRTC and encoder helper operations,
1689 <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
1691 The <function>drm_helper_connector_dpms</function> helper function
1692 is a connector <methodname>dpms</methodname> implementation that
1693 tracks power state of connectors. To use the function, drivers must
1694 provide <methodname>dpms</methodname> helper operations for CRTCs
1695 and encoders to apply the DPMS state to the device.
1698 The mid-layer doesn't track the power state of CRTCs and encoders.
1699 The <methodname>dpms</methodname> helper operations can thus be
1700 called with a mode identical to the currently active mode.
1704 <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
1705 uint32_t maxX, uint32_t maxY);</synopsis>
1707 The <function>drm_helper_probe_single_connector_modes</function> helper
1708 function is a connector <methodname>fill_modes</methodname>
1709 implementation that updates the connection status for the connector
1710 and then retrieves a list of modes by calling the connector
1711 <methodname>get_modes</methodname> helper operation.
1714 The function filters out modes larger than
1715 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1716 if specified. It then calls the connector
1717 <methodname>mode_valid</methodname> helper operation for each mode in
1718 the probed list to check whether the mode is valid for the connector.
1724 <title>CRTC Helper Operations</title>
1726 <listitem id="drm-helper-crtc-mode-fixup">
1727 <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
1728 const struct drm_display_mode *mode,
1729 struct drm_display_mode *adjusted_mode);</synopsis>
1731 Let CRTCs adjust the requested mode or reject it completely. This
1732 operation returns true if the mode is accepted (possibly after being
1733 adjusted) or false if it is rejected.
1736 The <methodname>mode_fixup</methodname> operation should reject the
1737 mode if it can't reasonably use it. The definition of "reasonable"
1738 is currently fuzzy in this context. One possible behaviour would be
1739 to set the adjusted mode to the panel timings when a fixed-mode
1740 panel is used with hardware capable of scaling. Another behaviour
1741 would be to accept any input mode and adjust it to the closest mode
1742 supported by the hardware (FIXME: This needs to be clarified).
1746 <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
1747 struct drm_framebuffer *old_fb)</synopsis>
1749 Move the CRTC on the current frame buffer (stored in
1750 <literal>crtc->fb</literal>) to position (x,y). Any of the frame
1751 buffer, x position or y position may have been modified.
1754 This helper operation is optional. If not provided, the
1755 <function>drm_crtc_helper_set_config</function> function will fall
1756 back to the <methodname>mode_set</methodname> helper operation.
1759 FIXME: Why are x and y passed as arguments, as they can be accessed
1760 through <literal>crtc->x</literal> and
1761 <literal>crtc->y</literal>?
1765 <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
1767 Prepare the CRTC for mode setting. This operation is called after
1768 validating the requested mode. Drivers use it to perform
1769 device-specific operations required before setting the new mode.
1773 <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
1774 struct drm_display_mode *adjusted_mode, int x, int y,
1775 struct drm_framebuffer *old_fb);</synopsis>
1777 Set a new mode, position and frame buffer. Depending on the device
1778 requirements, the mode can be stored internally by the driver and
1779 applied in the <methodname>commit</methodname> operation, or
1780 programmed to the hardware immediately.
1783 The <methodname>mode_set</methodname> operation returns 0 on success
1784 or a negative error code if an error occurs.
1788 <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
1790 Commit a mode. This operation is called after setting the new mode.
1791 Upon return the device must use the new mode and be fully
1798 <title>Encoder Helper Operations</title>
1801 <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
1802 const struct drm_display_mode *mode,
1803 struct drm_display_mode *adjusted_mode);</synopsis>
1805 FIXME: The mode argument be const, but the i915 driver modifies
1806 mode->clock in <function>intel_dp_mode_fixup</function>.
1809 Let encoders adjust the requested mode or reject it completely. This
1810 operation returns true if the mode is accepted (possibly after being
1811 adjusted) or false if it is rejected. See the
1812 <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
1813 operation</link> for an explanation of the allowed adjustments.
1817 <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
1819 Prepare the encoder for mode setting. This operation is called after
1820 validating the requested mode. Drivers use it to perform
1821 device-specific operations required before setting the new mode.
1825 <synopsis>void (*mode_set)(struct drm_encoder *encoder,
1826 struct drm_display_mode *mode,
1827 struct drm_display_mode *adjusted_mode);</synopsis>
1829 Set a new mode. Depending on the device requirements, the mode can
1830 be stored internally by the driver and applied in the
1831 <methodname>commit</methodname> operation, or programmed to the
1832 hardware immediately.
1836 <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
1838 Commit a mode. This operation is called after setting the new mode.
1839 Upon return the device must use the new mode and be fully
1846 <title>Connector Helper Operations</title>
1849 <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
1851 Return a pointer to the best encoder for the connecter. Device that
1852 map connectors to encoders 1:1 simply return the pointer to the
1853 associated encoder. This operation is mandatory.
1857 <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
1859 Fill the connector's <structfield>probed_modes</structfield> list
1860 by parsing EDID data with <function>drm_add_edid_modes</function> or
1861 calling <function>drm_mode_probed_add</function> directly for every
1862 supported mode and return the number of modes it has detected. This
1863 operation is mandatory.
1866 When adding modes manually the driver creates each mode with a call to
1867 <function>drm_mode_create</function> and must fill the following fields.
1870 <synopsis>__u32 type;</synopsis>
1872 Mode type bitmask, a combination of
1875 <term>DRM_MODE_TYPE_BUILTIN</term>
1876 <listitem><para>not used?</para></listitem>
1879 <term>DRM_MODE_TYPE_CLOCK_C</term>
1880 <listitem><para>not used?</para></listitem>
1883 <term>DRM_MODE_TYPE_CRTC_C</term>
1884 <listitem><para>not used?</para></listitem>
1888 DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
1891 <para>not used?</para>
1895 <term>DRM_MODE_TYPE_DEFAULT</term>
1896 <listitem><para>not used?</para></listitem>
1899 <term>DRM_MODE_TYPE_USERDEF</term>
1900 <listitem><para>not used?</para></listitem>
1903 <term>DRM_MODE_TYPE_DRIVER</term>
1906 The mode has been created by the driver (as opposed to
1907 to user-created modes).
1912 Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
1913 create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
1918 <synopsis>__u32 clock;</synopsis>
1919 <para>Pixel clock frequency in kHz unit</para>
1922 <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
1923 __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
1924 <para>Horizontal and vertical timing information</para>
1926 Active Front Sync Back
1928 <-----------------------><----------------><-------------><-------------->
1930 //////////////////////|
1931 ////////////////////// |
1932 ////////////////////// |.................. ................
1935 <----- [hv]display ----->
1936 <------------- [hv]sync_start ------------>
1937 <--------------------- [hv]sync_end --------------------->
1938 <-------------------------------- [hv]total ----------------------------->
1942 <synopsis>__u16 hskew;
1943 __u16 vscan;</synopsis>
1944 <para>Unknown</para>
1947 <synopsis>__u32 flags;</synopsis>
1949 Mode flags, a combination of
1952 <term>DRM_MODE_FLAG_PHSYNC</term>
1954 Horizontal sync is active high
1958 <term>DRM_MODE_FLAG_NHSYNC</term>
1960 Horizontal sync is active low
1964 <term>DRM_MODE_FLAG_PVSYNC</term>
1966 Vertical sync is active high
1970 <term>DRM_MODE_FLAG_NVSYNC</term>
1972 Vertical sync is active low
1976 <term>DRM_MODE_FLAG_INTERLACE</term>
1982 <term>DRM_MODE_FLAG_DBLSCAN</term>
1984 Mode uses doublescan
1988 <term>DRM_MODE_FLAG_CSYNC</term>
1990 Mode uses composite sync
1994 <term>DRM_MODE_FLAG_PCSYNC</term>
1996 Composite sync is active high
2000 <term>DRM_MODE_FLAG_NCSYNC</term>
2002 Composite sync is active low
2006 <term>DRM_MODE_FLAG_HSKEW</term>
2008 hskew provided (not used?)
2012 <term>DRM_MODE_FLAG_BCAST</term>
2018 <term>DRM_MODE_FLAG_PIXMUX</term>
2024 <term>DRM_MODE_FLAG_DBLCLK</term>
2030 <term>DRM_MODE_FLAG_CLKDIV2</term>
2038 Note that modes marked with the INTERLACE or DBLSCAN flags will be
2040 <function>drm_helper_probe_single_connector_modes</function> if
2041 the connector's <structfield>interlace_allowed</structfield> or
2042 <structfield>doublescan_allowed</structfield> field is set to 0.
2046 <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
2048 Mode name. The driver must call
2049 <function>drm_mode_set_name</function> to fill the mode name from
2050 <structfield>hdisplay</structfield>,
2051 <structfield>vdisplay</structfield> and interlace flag after
2052 filling the corresponding fields.
2058 The <structfield>vrefresh</structfield> value is computed by
2059 <function>drm_helper_probe_single_connector_modes</function>.
2062 When parsing EDID data, <function>drm_add_edid_modes</function> fill the
2063 connector <structfield>display_info</structfield>
2064 <structfield>width_mm</structfield> and
2065 <structfield>height_mm</structfield> fields. When creating modes
2066 manually the <methodname>get_modes</methodname> helper operation must
2067 set the <structfield>display_info</structfield>
2068 <structfield>width_mm</structfield> and
2069 <structfield>height_mm</structfield> fields if they haven't been set
2070 already (for instance at initilization time when a fixed-size panel is
2071 attached to the connector). The mode <structfield>width_mm</structfield>
2072 and <structfield>height_mm</structfield> fields are only used internally
2073 during EDID parsing and should not be set when creating modes manually.
2077 <synopsis>int (*mode_valid)(struct drm_connector *connector,
2078 struct drm_display_mode *mode);</synopsis>
2080 Verify whether a mode is valid for the connector. Return MODE_OK for
2081 supported modes and one of the enum drm_mode_status values (MODE_*)
2082 for unsupported modes. This operation is mandatory.
2085 As the mode rejection reason is currently not used beside for
2086 immediately removing the unsupported mode, an implementation can
2087 return MODE_BAD regardless of the exact reason why the mode is not
2091 Note that the <methodname>mode_valid</methodname> helper operation is
2092 only called for modes detected by the device, and
2093 <emphasis>not</emphasis> for modes set by the user through the CRTC
2094 <methodname>set_config</methodname> operation.
2101 <!-- Internals: vertical blanking -->
2103 <sect1 id="drm-vertical-blank">
2104 <title>Vertical Blanking</title>
2106 Vertical blanking plays a major role in graphics rendering. To achieve
2107 tear-free display, users must synchronize page flips and/or rendering to
2108 vertical blanking. The DRM API offers ioctls to perform page flips
2109 synchronized to vertical blanking and wait for vertical blanking.
2112 The DRM core handles most of the vertical blanking management logic, which
2113 involves filtering out spurious interrupts, keeping race-free blanking
2114 counters, coping with counter wrap-around and resets and keeping use
2115 counts. It relies on the driver to generate vertical blanking interrupts
2116 and optionally provide a hardware vertical blanking counter. Drivers must
2117 implement the following operations.
2121 <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
2122 void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
2124 Enable or disable vertical blanking interrupts for the given CRTC.
2128 <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
2130 Retrieve the value of the vertical blanking counter for the given
2131 CRTC. If the hardware maintains a vertical blanking counter its value
2132 should be returned. Otherwise drivers can use the
2133 <function>drm_vblank_count</function> helper function to handle this
2139 Drivers must initialize the vertical blanking handling core with a call to
2140 <function>drm_vblank_init</function> in their
2141 <methodname>load</methodname> operation. The function will set the struct
2142 <structname>drm_device</structname>
2143 <structfield>vblank_disable_allowed</structfield> field to 0. This will
2144 keep vertical blanking interrupts enabled permanently until the first mode
2145 set operation, where <structfield>vblank_disable_allowed</structfield> is
2146 set to 1. The reason behind this is not clear. Drivers can set the field
2147 to 1 after <function>calling drm_vblank_init</function> to make vertical
2148 blanking interrupts dynamically managed from the beginning.
2151 Vertical blanking interrupts can be enabled by the DRM core or by drivers
2152 themselves (for instance to handle page flipping operations). The DRM core
2153 maintains a vertical blanking use count to ensure that the interrupts are
2154 not disabled while a user still needs them. To increment the use count,
2155 drivers call <function>drm_vblank_get</function>. Upon return vertical
2156 blanking interrupts are guaranteed to be enabled.
2159 To decrement the use count drivers call
2160 <function>drm_vblank_put</function>. Only when the use count drops to zero
2161 will the DRM core disable the vertical blanking interrupts after a delay
2162 by scheduling a timer. The delay is accessible through the vblankoffdelay
2163 module parameter or the <varname>drm_vblank_offdelay</varname> global
2164 variable and expressed in milliseconds. Its default value is 5000 ms.
2167 When a vertical blanking interrupt occurs drivers only need to call the
2168 <function>drm_handle_vblank</function> function to account for the
2172 Resources allocated by <function>drm_vblank_init</function> must be freed
2173 with a call to <function>drm_vblank_cleanup</function> in the driver
2174 <methodname>unload</methodname> operation handler.
2178 <!-- Internals: open/close, file operations and ioctls -->
2181 <title>Open/Close, File Operations and IOCTLs</title>
2183 <title>Open and Close</title>
2184 <synopsis>int (*firstopen) (struct drm_device *);
2185 void (*lastclose) (struct drm_device *);
2186 int (*open) (struct drm_device *, struct drm_file *);
2187 void (*preclose) (struct drm_device *, struct drm_file *);
2188 void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
2189 <abstract>Open and close handlers. None of those methods are mandatory.
2192 The <methodname>firstopen</methodname> method is called by the DRM core
2193 when an application opens a device that has no other opened file handle.
2194 Similarly the <methodname>lastclose</methodname> method is called when
2195 the last application holding a file handle opened on the device closes
2196 it. Both methods are mostly used for UMS (User Mode Setting) drivers to
2197 acquire and release device resources which should be done in the
2198 <methodname>load</methodname> and <methodname>unload</methodname>
2199 methods for KMS drivers.
2202 Note that the <methodname>lastclose</methodname> method is also called
2203 at module unload time or, for hot-pluggable devices, when the device is
2204 unplugged. The <methodname>firstopen</methodname> and
2205 <methodname>lastclose</methodname> calls can thus be unbalanced.
2208 The <methodname>open</methodname> method is called every time the device
2209 is opened by an application. Drivers can allocate per-file private data
2210 in this method and store them in the struct
2211 <structname>drm_file</structname> <structfield>driver_priv</structfield>
2212 field. Note that the <methodname>open</methodname> method is called
2213 before <methodname>firstopen</methodname>.
2216 The close operation is split into <methodname>preclose</methodname> and
2217 <methodname>postclose</methodname> methods. Drivers must stop and
2218 cleanup all per-file operations in the <methodname>preclose</methodname>
2219 method. For instance pending vertical blanking and page flip events must
2220 be cancelled. No per-file operation is allowed on the file handle after
2221 returning from the <methodname>preclose</methodname> method.
2224 Finally the <methodname>postclose</methodname> method is called as the
2225 last step of the close operation, right before calling the
2226 <methodname>lastclose</methodname> method if no other open file handle
2227 exists for the device. Drivers that have allocated per-file private data
2228 in the <methodname>open</methodname> method should free it here.
2231 The <methodname>lastclose</methodname> method should restore CRTC and
2232 plane properties to default value, so that a subsequent open of the
2233 device will not inherit state from the previous user.
2237 <title>File Operations</title>
2238 <synopsis>const struct file_operations *fops</synopsis>
2239 <abstract>File operations for the DRM device node.</abstract>
2241 Drivers must define the file operations structure that forms the DRM
2242 userspace API entry point, even though most of those operations are
2243 implemented in the DRM core. The <methodname>open</methodname>,
2244 <methodname>release</methodname> and <methodname>ioctl</methodname>
2245 operations are handled by
2247 .owner = THIS_MODULE,
2249 .release = drm_release,
2250 .unlocked_ioctl = drm_ioctl,
2251 #ifdef CONFIG_COMPAT
2252 .compat_ioctl = drm_compat_ioctl,
2257 Drivers that implement private ioctls that requires 32/64bit
2258 compatibility support must provide their own
2259 <methodname>compat_ioctl</methodname> handler that processes private
2260 ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
2263 The <methodname>read</methodname> and <methodname>poll</methodname>
2264 operations provide support for reading DRM events and polling them. They
2269 .fasync = drm_fasync,
2270 .llseek = no_llseek,
2274 The memory mapping implementation varies depending on how the driver
2275 manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
2276 while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
2277 <xref linkend="drm-gem"/>.
2279 .mmap = drm_gem_mmap,
2283 No other file operation is supported by the DRM API.
2287 <title>IOCTLs</title>
2288 <synopsis>struct drm_ioctl_desc *ioctls;
2289 int num_ioctls;</synopsis>
2290 <abstract>Driver-specific ioctls descriptors table.</abstract>
2292 Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
2293 descriptors table is indexed by the ioctl number offset from the base
2294 value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
2298 <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
2300 <parameter>ioctl</parameter> is the ioctl name. Drivers must define
2301 the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
2302 offset from DRM_COMMAND_BASE and the ioctl number respectively. The
2303 first macro is private to the device while the second must be exposed
2304 to userspace in a public header.
2307 <parameter>func</parameter> is a pointer to the ioctl handler function
2308 compatible with the <type>drm_ioctl_t</type> type.
2309 <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
2310 struct drm_file *file_priv);</programlisting>
2313 <parameter>flags</parameter> is a bitmask combination of the following
2314 values. It restricts how the ioctl is allowed to be called.
2317 DRM_AUTH - Only authenticated callers allowed
2320 DRM_MASTER - The ioctl can only be called on the master file
2324 DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
2327 DRM_CONTROL_ALLOW - The ioctl can only be called on a control
2331 DRM_UNLOCKED - The ioctl handler will be called without locking
2332 the DRM global mutex
2341 <title>Command submission & fencing</title>
2343 This should cover a few device-specific command submission
2348 <!-- Internals: suspend/resume -->
2351 <title>Suspend/Resume</title>
2353 The DRM core provides some suspend/resume code, but drivers wanting full
2354 suspend/resume support should provide save() and restore() functions.
2355 These are called at suspend, hibernate, or resume time, and should perform
2356 any state save or restore required by your device across suspend or
2359 <synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
2360 int (*resume) (struct drm_device *);</synopsis>
2362 Those are legacy suspend and resume methods. New driver should use the
2363 power management interface provided by their bus type (usually through
2364 the struct <structname>device_driver</structname> dev_pm_ops) and set
2365 these methods to NULL.
2370 <title>DMA services</title>
2372 This should cover how DMA mapping etc. is supported by the core.
2373 These functions are deprecated and should not be used.
2381 - Document the struct_mutex catch-all lock
2382 - Document connector properties
2384 - Why is the load method optional?
2385 - What are drivers supposed to set the initial display state to, and how?
2386 Connector's DPMS states are not initialized and are thus equal to
2387 DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
2388 drm_helper_disable_unused_functions(), which disables unused encoders and
2389 CRTCs, but doesn't touch the connectors' DPMS state, and
2390 drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
2391 that don't implement (or just don't use) fbcon compatibility need to call
2392 those functions themselves?
2393 - KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
2394 around mode setting. Should this be done in the DRM core?
2395 - vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
2396 call and never set back to 0. It seems to be safe to permanently set it to 1
2397 in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
2398 well. This should be investigated.
2399 - crtc and connector .save and .restore operations are only used internally in
2400 drivers, should they be removed from the core?
2401 - encoder mid-layer .save and .restore operations are only used internally in
2402 drivers, should they be removed from the core?
2403 - encoder mid-layer .detect operation is only used internally in drivers,
2404 should it be removed from the core?
2407 <!-- External interfaces -->
2409 <chapter id="drmExternals">
2410 <title>Userland interfaces</title>
2412 The DRM core exports several interfaces to applications,
2413 generally intended to be used through corresponding libdrm
2414 wrapper functions. In addition, drivers export device-specific
2415 interfaces for use by userspace drivers & device-aware
2416 applications through ioctls and sysfs files.
2419 External interfaces include: memory mapping, context management,
2420 DMA operations, AGP management, vblank control, fence
2421 management, memory management, and output management.
2424 Cover generic ioctls and sysfs layout here. We only need high-level
2425 info, since man pages should cover the rest.
2428 <!-- External: vblank handling -->
2431 <title>VBlank event handling</title>
2433 The DRM core exposes two vertical blank related ioctls:
2436 <term>DRM_IOCTL_WAIT_VBLANK</term>
2439 This takes a struct drm_wait_vblank structure as its argument,
2440 and it is used to block or request a signal when a specified
2441 vblank event occurs.
2446 <term>DRM_IOCTL_MODESET_CTL</term>
2449 This should be called by application level drivers before and
2450 after mode setting, since on many devices the vertical blank
2451 counter is reset at that time. Internally, the DRM snapshots
2452 the last vblank count when the ioctl is called with the
2453 _DRM_PRE_MODESET command, so that the counter won't go backwards
2454 (which is dealt with when _DRM_POST_MODESET is used).
2459 <!--!Edrivers/char/drm/drm_irq.c-->
2465 <!-- API reference -->
2467 <appendix id="drmDriverApi">
2468 <title>DRM Driver API</title>
2470 Include auto-generated API reference here (need to reference it
2471 from paragraphs above too).
git.samba.org / sfrench / cifs-2.6.git / blob