1 .. -*- coding: utf-8; mode: rst -*-
5 *******************************************************************
6 ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
7 *******************************************************************
12 VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items
18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp )
20 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp )
22 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_querymenu *argp )
29 File descriptor returned by :ref:`open() <func-open>`.
32 VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU
40 To query the attributes of a control applications set the ``id`` field
41 of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the
42 ``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver
43 fills the rest of the structure or returns an ``EINVAL`` error code when the
46 It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL``
47 with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and
48 exclusive ``V4L2_CID_LASTP1``. Drivers may return ``EINVAL`` if a control in
49 this range is not supported. Further applications can enumerate private
50 controls, which are not defined in this specification, by starting at
51 ``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver
54 In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag
55 in the ``flags`` field this control is permanently disabled and should
56 be ignored by the application. [#f1]_
58 When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the
59 driver returns the next supported non-compound control, or ``EINVAL`` if
60 there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag
61 can be specified to enumerate all compound controls (i.e. controls with
62 type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words
63 controls that contain more than one value). Specify both
64 ``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in
65 order to enumerate all controls, compound or not. Drivers which do not
66 support these flags yet always return ``EINVAL``.
68 The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better
69 support controls that can use compound types, and to expose additional
70 control information that cannot be returned in struct
71 :ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full.
73 ``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as
74 ``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed
77 Additional information is required for menu controls: the names of the
78 menu items. To query them applications set the ``id`` and ``index``
79 fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the
80 ``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver
81 fills the rest of the structure or returns an ``EINVAL`` error code when the
82 ``id`` or ``index`` is invalid. Menu items are enumerated by calling
83 ``VIDIOC_QUERYMENU`` with successive ``index`` values from struct
84 :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``,
87 .. note:: It is possible for ``VIDIOC_QUERYMENU`` to return
88 an ``EINVAL`` error code for some indices between ``minimum`` and
89 ``maximum``. In that case that particular menu item is not supported by
90 this driver. Also note that the ``minimum`` value is not necessarily 0.
92 See also the examples in :ref:`control`.
97 .. flat-table:: struct v4l2_queryctrl
109 - Identifies the control, set by the application. See
110 :ref:`control-id` for predefined IDs. When the ID is ORed with
111 V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and
112 returns the first control with a higher ID. Drivers which do not
113 support this flag yet always return an ``EINVAL`` error code.
121 - Type of control, see :ref:`v4l2-ctrl-type`.
129 - Name of the control, a NUL-terminated ASCII string. This
130 information is intended for the user.
138 - Minimum value, inclusive. This field gives a lower bound for the
139 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
140 the minimum value is to be used for each possible control type.
141 Note that this a signed 32-bit value.
149 - Maximum value, inclusive. This field gives an upper bound for the
150 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
151 the maximum value is to be used for each possible control type.
152 Note that this a signed 32-bit value.
160 - This field gives a step size for the control. See enum
161 :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
162 to be used for each possible control type. Note that this an
163 unsigned 32-bit value.
165 Generally drivers should not scale hardware control values. It may
166 be necessary for example when the ``name`` or ``id`` imply a
167 particular unit and the hardware actually accepts only multiples
168 of said unit. If so, drivers must take care values are properly
169 rounded when scaling, such that errors will not accumulate on
170 repeated read-write cycles.
172 This field gives the smallest change of an integer control
173 actually affecting hardware. Often the information is needed when
174 the user can change controls by keyboard or GUI buttons, rather
175 than a slider. When for example a hardware register accepts values
176 0-511 and the driver reports 0-65535, step should be 128.
178 Note that although signed, the step value is supposed to be always
187 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
188 ``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
189 for other types of controls.
191 .. note:: Drivers reset controls to their default value only when
192 the driver is first loaded, never afterwards.
200 - Control flags, see :ref:`control-flags`.
208 - Reserved for future extensions. Drivers must set the array to
213 .. _v4l2-query-ext-ctrl:
215 .. flat-table:: struct v4l2_query_ext_ctrl
227 - Identifies the control, set by the application. See
228 :ref:`control-id` for predefined IDs. When the ID is ORed with
229 ``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and
230 returns the first non-compound control with a higher ID. When the
231 ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears
232 the flag and returns the first compound control with a higher ID.
233 Set both to get the first control (compound or not) with a higher
242 - Type of control, see :ref:`v4l2-ctrl-type`.
250 - Name of the control, a NUL-terminated ASCII string. This
251 information is intended for the user.
259 - Minimum value, inclusive. This field gives a lower bound for the
260 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
261 the minimum value is to be used for each possible control type.
262 Note that this a signed 64-bit value.
270 - Maximum value, inclusive. This field gives an upper bound for the
271 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
272 the maximum value is to be used for each possible control type.
273 Note that this a signed 64-bit value.
281 - This field gives a step size for the control. See enum
282 :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
283 to be used for each possible control type. Note that this an
284 unsigned 64-bit value.
286 Generally drivers should not scale hardware control values. It may
287 be necessary for example when the ``name`` or ``id`` imply a
288 particular unit and the hardware actually accepts only multiples
289 of said unit. If so, drivers must take care values are properly
290 rounded when scaling, such that errors will not accumulate on
291 repeated read-write cycles.
293 This field gives the smallest change of an integer control
294 actually affecting hardware. Often the information is needed when
295 the user can change controls by keyboard or GUI buttons, rather
296 than a slider. When for example a hardware register accepts values
297 0-511 and the driver reports 0-65535, step should be 128.
305 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
306 ``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
307 or ``_U16`` control. Not valid for other types of controls.
309 .. note:: Drivers reset controls to their default value only when
310 the driver is first loaded, never afterwards.
318 - Control flags, see :ref:`control-flags`.
326 - The size in bytes of a single element of the array. Given a char
327 pointer ``p`` to a 3-dimensional array you can find the position
328 of cell ``(z, y, x)`` as follows:
329 ``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``.
330 ``elem_size`` is always valid, also when the control isn't an
331 array. For string controls ``elem_size`` is equal to
340 - The number of elements in the N-dimensional array. If this control
341 is not an array, then ``elems`` is 1. The ``elems`` field can
350 - The number of dimension in the N-dimensional array. If this
351 control is not an array, then this field is 0.
357 - ``dims[V4L2_CTRL_MAX_DIMS]``
359 - The size of each dimension. The first ``nr_of_dims`` elements of
360 this array must be non-zero, all remaining elements must be zero.
368 - Reserved for future extensions. Applications and drivers must set
375 .. flat-table:: struct v4l2_querymenu
388 - Identifies the control, set by the application from the respective
389 struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
398 - Index of the menu item, starting at zero, set by the application.
415 - Name of the menu item, a NUL-terminated ASCII string. This
416 information is intended for the user. This field is valid for
417 ``V4L2_CTRL_FLAG_MENU`` type controls.
426 - Value of the integer menu item. This field is valid for
427 ``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls.
436 - Reserved for future extensions. Drivers must set the array to
443 .. flat-table:: enum v4l2_ctrl_type
463 - ``V4L2_CTRL_TYPE_INTEGER``
471 - An integer-valued control ranging from minimum to maximum
472 inclusive. The step value indicates the increment between values.
476 - ``V4L2_CTRL_TYPE_BOOLEAN``
484 - A boolean-valued control. Zero corresponds to "disabled", and one
489 - ``V4L2_CTRL_TYPE_MENU``
497 - The control has a menu of N choices. The names of the menu items
498 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
502 - ``V4L2_CTRL_TYPE_INTEGER_MENU``
510 - The control has a menu of N choices. The values of the menu items
511 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is
512 similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings,
513 the menu items are signed 64-bit integers.
517 - ``V4L2_CTRL_TYPE_BITMASK``
525 - A bitmask field. The maximum value is the set of bits that can be
526 used, all other bits are to be 0. The maximum value is interpreted
527 as a __u32, allowing the use of bit 31 in the bitmask.
531 - ``V4L2_CTRL_TYPE_BUTTON``
539 - A control which performs an action when set. Drivers must ignore
540 the value passed with ``VIDIOC_S_CTRL`` and return an ``EINVAL`` error
541 code on a ``VIDIOC_G_CTRL`` attempt.
545 - ``V4L2_CTRL_TYPE_INTEGER64``
553 - A 64-bit integer valued control. Minimum, maximum and step size
554 cannot be queried using ``VIDIOC_QUERYCTRL``. Only
555 ``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step
556 values, they should be interpreted as n/a when using
557 ``VIDIOC_QUERYCTRL``.
561 - ``V4L2_CTRL_TYPE_STRING``
569 - The minimum and maximum string lengths. The step size means that
570 the string must be (minimum + N * step) characters long for N ≥ 0.
571 These lengths do not include the terminating zero, so in order to
572 pass a string of length 8 to
573 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
574 set the ``size`` field of struct
575 :ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
576 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
577 the ``size`` field to ``maximum`` + 1. Which character encoding is
578 used will depend on the string control itself and should be part
579 of the control documentation.
583 - ``V4L2_CTRL_TYPE_CTRL_CLASS``
591 - This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a
592 control ID equal to a control class code (see :ref:`ctrl-class`)
593 + 1, the ioctl returns the name of the control class and this
594 control type. Older drivers which do not support this feature
595 return an ``EINVAL`` error code.
599 - ``V4L2_CTRL_TYPE_U8``
607 - An unsigned 8-bit valued control ranging from minimum to maximum
608 inclusive. The step value indicates the increment between values.
612 - ``V4L2_CTRL_TYPE_U16``
620 - An unsigned 16-bit valued control ranging from minimum to maximum
621 inclusive. The step value indicates the increment between values.
625 - ``V4L2_CTRL_TYPE_U32``
633 - An unsigned 32-bit valued control ranging from minimum to maximum
634 inclusive. The step value indicates the increment between values.
640 .. flat-table:: Control Flags
648 - ``V4L2_CTRL_FLAG_DISABLED``
652 - This control is permanently disabled and should be ignored by the
653 application. Any attempt to change the control will result in an
654 ``EINVAL`` error code.
658 - ``V4L2_CTRL_FLAG_GRABBED``
662 - This control is temporarily unchangeable, for example because
663 another application took over control of the respective resource.
664 Such controls may be displayed specially in a user interface.
665 Attempts to change the control may result in an ``EBUSY`` error code.
669 - ``V4L2_CTRL_FLAG_READ_ONLY``
673 - This control is permanently readable only. Any attempt to change
674 the control will result in an ``EINVAL`` error code.
678 - ``V4L2_CTRL_FLAG_UPDATE``
682 - A hint that changing this control may affect the value of other
683 controls within the same control class. Applications should update
684 their user interface accordingly.
688 - ``V4L2_CTRL_FLAG_INACTIVE``
692 - This control is not applicable to the current configuration and
693 should be displayed accordingly in a user interface. For example
694 the flag may be set on a MPEG audio level 2 bitrate control when
695 MPEG audio encoding level 1 was selected with another control.
699 - ``V4L2_CTRL_FLAG_SLIDER``
703 - A hint that this control is best represented as a slider-like
704 element in a user interface.
708 - ``V4L2_CTRL_FLAG_WRITE_ONLY``
712 - This control is permanently writable only. Any attempt to read the
713 control will result in an ``EACCES`` error code error code. This flag
714 is typically present for relative controls or action controls
715 where writing a value will cause the device to carry out a given
716 action (e. g. motor control) but no meaningful value can be
721 - ``V4L2_CTRL_FLAG_VOLATILE``
725 - This control is volatile, which means that the value of the
726 control changes continuously. A typical example would be the
727 current gain value if the device is in auto-gain mode. In such a
728 case the hardware calculates the gain value based on the lighting
729 conditions which can change over time.
731 .. note:: Setting a new value for a volatile control will have no
732 effect and no ``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless
733 the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is
734 also set. Otherwise the new value will just be ignored.
738 - ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
742 - This control has a pointer type, so its value has to be accessed
743 using one of the pointer fields of struct
744 :ref:`v4l2_ext_control <v4l2-ext-control>`. This flag is set
745 for controls that are an array, string, or have a compound type.
746 In all cases you have to set a pointer to memory containing the
747 payload of the control.
751 - ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
755 - The value provided to the control will be propagated to the driver
756 even if it remains constant. This is required when the control
757 represents an action on the hardware. For example: clearing an
758 error flag or triggering the flash. All the controls of the type
759 ``V4L2_CTRL_TYPE_BUTTON`` have this flag set.
765 On success 0 is returned, on error -1 and the ``errno`` variable is set
766 appropriately. The generic error codes are described at the
767 :ref:`Generic Error Codes <gen-errors>` chapter.
770 The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is
771 invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id``
772 is invalid or ``index`` is out of range (less than ``minimum`` or
773 greater than ``maximum``) or this particular menu item is not
774 supported by the driver.
777 An attempt was made to read a write-only control.
780 ``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers
781 can skip predefined controls not supported by the hardware (although
782 returning ``EINVAL`` would do as well), or disable predefined and private
783 controls after hardware detection without the trouble of reordering
784 control arrays and indices (``EINVAL`` cannot be used to skip private
785 controls because it would prematurely end the enumeration).
git.samba.org / sfrench / cifs-2.6.git / blob