1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_G_EXT_CTRLS:
5
6******************************************************************
7ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
8******************************************************************
9
10Name
11====
12
13VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_G_EXT_CTRLS
19
20``int ioctl(int fd, VIDIOC_G_EXT_CTRLS, struct v4l2_ext_controls *argp)``
21
22.. c:macro:: VIDIOC_S_EXT_CTRLS
23
24``int ioctl(int fd, VIDIOC_S_EXT_CTRLS, struct v4l2_ext_controls *argp)``
25
26.. c:macro:: VIDIOC_TRY_EXT_CTRLS
27
28``int ioctl(int fd, VIDIOC_TRY_EXT_CTRLS, struct v4l2_ext_controls *argp)``
29
30Arguments
31=========
32
33``fd``
34    File descriptor returned by :c:func:`open()`.
35
36``argp``
37    Pointer to struct :c:type:`v4l2_ext_controls`.
38
39Description
40===========
41
42These ioctls allow the caller to get or set multiple controls
43atomically. Control IDs are grouped into control classes (see
44:ref:`ctrl-class`) and all controls in the control array must belong
45to the same control class.
46
47Applications must always fill in the ``count``, ``which``, ``controls``
48and ``reserved`` fields of struct
49:c:type:`v4l2_ext_controls`, and initialize the
50struct :c:type:`v4l2_ext_control` array pointed to
51by the ``controls`` fields.
52
53To get the current value of a set of controls applications initialize
54the ``id``, ``size`` and ``reserved2`` fields of each struct
55:c:type:`v4l2_ext_control` and call the
56:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls must also set the
57``string`` field. Controls of compound types
58(``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
59
60If the ``size`` is too small to receive the control result (only
61relevant for pointer-type controls like strings), then the driver will
62set ``size`` to a valid value and return an ``ENOSPC`` error code. You
63should re-allocate the memory to this new size and try again. For the
64string type it is possible that the same issue occurs again if the
65string has grown in the meantime. It is recommended to call
66:ref:`VIDIOC_QUERYCTRL` first and use
67``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is
68sufficient memory.
69
70N-dimensional arrays are set and retrieved row-by-row. You cannot set a
71partial array, all elements have to be set or retrieved. The total size
72is calculated as ``elems`` * ``elem_size``. These values can be obtained
73by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
74
75To change the value of a set of controls applications initialize the
76``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
77of each struct :c:type:`v4l2_ext_control` and call
78the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
79control values are valid.
80
81To check if a set of controls have correct values applications
82initialize the ``id``, ``size``, ``reserved2`` and
83``value/value64/string/ptr`` fields of each struct
84:c:type:`v4l2_ext_control` and call the
85:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
86values are automatically adjusted to a valid value or if an error is
87returned.
88
89When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error
90code. When the value is out of bounds drivers can choose to take the
91closest valid value or return an ``ERANGE`` error code, whatever seems more
92appropriate. In the first case the new value is set in struct
93:c:type:`v4l2_ext_control`. If the new control value
94is inappropriate (e.g. the given menu index is not supported by the menu
95control), then this will also result in an ``EINVAL`` error code error.
96
97If ``request_fd`` is set to a not-yet-queued :ref:`request <media-request-api>`
98file descriptor and ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``,
99then the controls are not applied immediately when calling
100:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, but instead are applied by
101the driver for the buffer associated with the same request.
102If the device does not support requests, then ``EACCES`` will be returned.
103If requests are supported but an invalid request file descriptor is given,
104then ``EINVAL`` will be returned.
105
106An attempt to call :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` for a
107request that has already been queued will result in an ``EBUSY`` error.
108
109If ``request_fd`` is specified and ``which`` is set to
110``V4L2_CTRL_WHICH_REQUEST_VAL`` during a call to
111:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then it will return the
112values of the controls at the time of request completion.
113If the request is not yet completed, then this will result in an
114``EACCES`` error.
115
116The driver will only set/get these controls if all control values are
117correct. This prevents the situation where only some of the controls
118were set/get. Only low-level errors (e. g. a failed i2c command) can
119still cause this situation.
120
121.. tabularcolumns:: |p{6.8cm}|p{4.0cm}|p{6.5cm}|
122
123.. c:type:: v4l2_ext_control
124
125.. raw:: latex
126
127   \footnotesize
128
129.. cssclass:: longtable
130
131.. flat-table:: struct v4l2_ext_control
132    :header-rows:  0
133    :stub-columns: 0
134    :widths:       1 1 2
135
136    * - __u32
137      - ``id``
138      - Identifies the control, set by the application.
139    * - __u32
140      - ``size``
141      - The total size in bytes of the payload of this control.
142    * - :cspan:`2` The ``size`` field is normally 0, but for pointer
143	controls this should be set to the size of the memory that contains
144	the payload or that will receive the payload.
145	If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value
146	is less than is required to store the payload result, then it is set
147	to a value large enough to store the payload result and ``ENOSPC`` is
148	returned.
149
150	.. note::
151
152	   For string controls, this ``size`` field should
153	   not be confused with the length of the string. This field refers
154	   to the size of the memory that contains the string. The actual
155	   *length* of the string may well be much smaller.
156    * - __u32
157      - ``reserved2``\ [1]
158      - Reserved for future extensions. Drivers and applications must set
159	the array to zero.
160    * - union {
161      - (anonymous)
162    * - __s32
163      - ``value``
164      - New value or current value. Valid if this control is not of type
165	``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
166	not set.
167    * - __s64
168      - ``value64``
169      - New value or current value. Valid if this control is of type
170	``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
171	not set.
172    * - char *
173      - ``string``
174      - A pointer to a string. Valid if this control is of type
175	``V4L2_CTRL_TYPE_STRING``.
176    * - __u8 *
177      - ``p_u8``
178      - A pointer to a matrix control of unsigned 8-bit values. Valid if
179	this control is of type ``V4L2_CTRL_TYPE_U8``.
180    * - __u16 *
181      - ``p_u16``
182      - A pointer to a matrix control of unsigned 16-bit values. Valid if
183	this control is of type ``V4L2_CTRL_TYPE_U16``.
184    * - __u32 *
185      - ``p_u32``
186      - A pointer to a matrix control of unsigned 32-bit values. Valid if
187	this control is of type ``V4L2_CTRL_TYPE_U32``.
188    * - struct :c:type:`v4l2_area` *
189      - ``p_area``
190      - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
191        of type ``V4L2_CTRL_TYPE_AREA``.
192    * - struct :c:type:`v4l2_ctrl_h264_sps` *
193      - ``p_h264_sps``
194      - A pointer to a struct :c:type:`v4l2_ctrl_h264_sps`. Valid if this control is
195        of type ``V4L2_CTRL_TYPE_H264_SPS``.
196    * - struct :c:type:`v4l2_ctrl_h264_pps` *
197      - ``p_h264_pps``
198      - A pointer to a struct :c:type:`v4l2_ctrl_h264_pps`. Valid if this control is
199        of type ``V4L2_CTRL_TYPE_H264_PPS``.
200    * - struct :c:type:`v4l2_ctrl_h264_scaling_matrix` *
201      - ``p_h264_scaling_matrix``
202      - A pointer to a struct :c:type:`v4l2_ctrl_h264_scaling_matrix`. Valid if this control is
203        of type ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX``.
204    * - struct :c:type:`v4l2_ctrl_h264_pred_weights` *
205      - ``p_h264_pred_weights``
206      - A pointer to a struct :c:type:`v4l2_ctrl_h264_pred_weights`. Valid if this control is
207        of type ``V4L2_CTRL_TYPE_H264_PRED_WEIGHTS``.
208    * - struct :c:type:`v4l2_ctrl_h264_slice_params` *
209      - ``p_h264_slice_params``
210      - A pointer to a struct :c:type:`v4l2_ctrl_h264_slice_params`. Valid if this control is
211        of type ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS``.
212    * - struct :c:type:`v4l2_ctrl_h264_decode_params` *
213      - ``p_h264_decode_params``
214      - A pointer to a struct :c:type:`v4l2_ctrl_h264_decode_params`. Valid if this control is
215        of type ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS``.
216    * - struct :c:type:`v4l2_ctrl_fwht_params` *
217      - ``p_fwht_params``
218      - A pointer to a struct :c:type:`v4l2_ctrl_fwht_params`. Valid if this control is
219        of type ``V4L2_CTRL_TYPE_FWHT_PARAMS``.
220    * - struct :c:type:`v4l2_ctrl_vp8_frame` *
221      - ``p_vp8_frame``
222      - A pointer to a struct :c:type:`v4l2_ctrl_vp8_frame`. Valid if this control is
223        of type ``V4L2_CTRL_TYPE_VP8_FRAME``.
224    * - struct :c:type:`v4l2_ctrl_mpeg2_sequence` *
225      - ``p_mpeg2_sequence``
226      - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_sequence`. Valid if this control is
227        of type ``V4L2_CTRL_TYPE_MPEG2_SEQUENCE``.
228    * - struct :c:type:`v4l2_ctrl_mpeg2_picture` *
229      - ``p_mpeg2_picture``
230      - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_picture`. Valid if this control is
231        of type ``V4L2_CTRL_TYPE_MPEG2_PICTURE``.
232    * - struct :c:type:`v4l2_ctrl_mpeg2_quantisation` *
233      - ``p_mpeg2_quantisation``
234      - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_quantisation`. Valid if this control is
235        of type ``V4L2_CTRL_TYPE_MPEG2_QUANTISATION``.
236    * - struct :c:type:`v4l2_ctrl_vp9_compressed_hdr` *
237      - ``p_vp9_compressed_hdr_probs``
238      - A pointer to a struct :c:type:`v4l2_ctrl_vp9_compressed_hdr`. Valid if this
239        control is of type ``V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR``.
240    * - struct :c:type:`v4l2_ctrl_vp9_frame` *
241      - ``p_vp9_frame``
242      - A pointer to a struct :c:type:`v4l2_ctrl_vp9_frame`. Valid if this
243        control is of type ``V4L2_CTRL_TYPE_VP9_FRAME``.
244    * - struct :c:type:`v4l2_ctrl_hdr10_cll_info` *
245      - ``p_hdr10_cll``
246      - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_cll_info`. Valid if this control is
247        of type ``V4L2_CTRL_TYPE_HDR10_CLL_INFO``.
248    * - struct :c:type:`v4l2_ctrl_hdr10_mastering_display` *
249      - ``p_hdr10_mastering``
250      - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_mastering_display`. Valid if this control is
251        of type ``V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY``.
252    * - void *
253      - ``ptr``
254      - A pointer to a compound type which can be an N-dimensional array
255	and/or a compound type (the control's type is >=
256	``V4L2_CTRL_COMPOUND_TYPES``). Valid if
257	``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
258    * - }
259      -
260
261.. raw:: latex
262
263   \normalsize
264
265.. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8cm}|
266
267.. c:type:: v4l2_ext_controls
268
269.. cssclass:: longtable
270
271.. flat-table:: struct v4l2_ext_controls
272    :header-rows:  0
273    :stub-columns: 0
274    :widths:       1 1 2
275
276    * - union {
277      - (anonymous)
278    * - __u32
279      - ``which``
280      - Which value of the control to get/set/try.
281    * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
282	the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
283	value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
284	these controls have to be retrieved from a request or tried/set for
285	a request. In the latter case the ``request_fd`` field contains the
286	file descriptor of the request that should be used. If the device
287	does not support requests, then ``EACCES`` will be returned.
288
289	When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
290	get the default value of the control, you cannot set or try it.
291
292	For backwards compatibility you can also use a control class here
293	(see :ref:`ctrl-class`). In that case all controls have to
294	belong to that control class. This usage is deprecated, instead
295	just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
296	drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
297	that require a control class here. You can test for such drivers
298	by setting ``which`` to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
299	:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a count of 0.
300	If that fails, then the driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
301    * - __u32
302      - ``ctrl_class``
303      - Deprecated name kept for backwards compatibility. Use ``which`` instead.
304    * - }
305      -
306    * - __u32
307      - ``count``
308      - The number of controls in the controls array. May also be zero.
309    * - __u32
310      - ``error_idx``
311      - Index of the failing control. Set by the driver in case of an error.
312    * - :cspan:`2` If the error is associated
313	with a particular control, then ``error_idx`` is set to the index
314	of that control. If the error is not related to a specific
315	control, or the validation step failed (see below), then
316	``error_idx`` is set to ``count``. The value is undefined if the
317	ioctl returned 0 (success).
318
319	Before controls are read from/written to hardware a validation
320	step takes place: this checks if all controls in the list are
321	valid controls, if no attempt is made to write to a read-only
322	control or read from a write-only control, and any other up-front
323	checks that can be done without accessing the hardware. The exact
324	validations done during this step are driver dependent since some
325	checks might require hardware access for some devices, thus making
326	it impossible to do those checks up-front. However, drivers should
327	make a best-effort to do as many up-front checks as possible.
328
329	This check is done to avoid leaving the hardware in an
330	inconsistent state due to easy-to-avoid problems. But it leads to
331	another problem: the application needs to know whether an error
332	came from the validation step (meaning that the hardware was not
333	touched) or from an error during the actual reading from/writing
334	to hardware.
335
336	The, in hindsight quite poor, solution for that is to set
337	``error_idx`` to ``count`` if the validation failed. This has the
338	unfortunate side-effect that it is not possible to see which
339	control failed the validation. If the validation was successful
340	and the error happened while accessing the hardware, then
341	``error_idx`` is less than ``count`` and only the controls up to
342	``error_idx-1`` were read or written correctly, and the state of
343	the remaining controls is undefined.
344
345	Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
346	also no need to handle the validation step in this special way, so
347	``error_idx`` will just be set to the control that failed the
348	validation step instead of to ``count``. This means that if
349	:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
350	then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
351	actual control that failed the validation step. Unfortunately,
352	there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
353    * - __s32
354      - ``request_fd``
355      - File descriptor of the request to be used by this operation. Only
356	valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``.
357	If the device does not support requests, then ``EACCES`` will be returned.
358	If requests are supported but an invalid request file descriptor is
359	given, then ``EINVAL`` will be returned.
360    * - __u32
361      - ``reserved``\ [1]
362      - Reserved for future extensions.
363
364	Drivers and applications must set the array to zero.
365    * - struct :c:type:`v4l2_ext_control` *
366      - ``controls``
367      - Pointer to an array of ``count`` v4l2_ext_control structures.
368
369	Ignored if ``count`` equals zero.
370
371.. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm}|
372
373.. cssclass:: longtable
374
375.. _ctrl-class:
376
377.. flat-table:: Control classes
378    :header-rows:  0
379    :stub-columns: 0
380    :widths:       3 1 4
381
382    * - ``V4L2_CTRL_CLASS_USER``
383      - 0x980000
384      - The class containing user controls. These controls are described
385	in :ref:`control`. All controls that can be set using the
386	:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
387	:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
388	class.
389    * - ``V4L2_CTRL_CLASS_CODEC``
390      - 0x990000
391      - The class containing stateful codec controls. These controls are
392	described in :ref:`codec-controls`.
393    * - ``V4L2_CTRL_CLASS_CAMERA``
394      - 0x9a0000
395      - The class containing camera controls. These controls are described
396	in :ref:`camera-controls`.
397    * - ``V4L2_CTRL_CLASS_FM_TX``
398      - 0x9b0000
399      - The class containing FM Transmitter (FM TX) controls. These
400	controls are described in :ref:`fm-tx-controls`.
401    * - ``V4L2_CTRL_CLASS_FLASH``
402      - 0x9c0000
403      - The class containing flash device controls. These controls are
404	described in :ref:`flash-controls`.
405    * - ``V4L2_CTRL_CLASS_JPEG``
406      - 0x9d0000
407      - The class containing JPEG compression controls. These controls are
408	described in :ref:`jpeg-controls`.
409    * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
410      - 0x9e0000
411      - The class containing image source controls. These controls are
412	described in :ref:`image-source-controls`.
413    * - ``V4L2_CTRL_CLASS_IMAGE_PROC``
414      - 0x9f0000
415      - The class containing image processing controls. These controls are
416	described in :ref:`image-process-controls`.
417    * - ``V4L2_CTRL_CLASS_FM_RX``
418      - 0xa10000
419      - The class containing FM Receiver (FM RX) controls. These controls
420	are described in :ref:`fm-rx-controls`.
421    * - ``V4L2_CTRL_CLASS_RF_TUNER``
422      - 0xa20000
423      - The class containing RF tuner controls. These controls are
424	described in :ref:`rf-tuner-controls`.
425    * - ``V4L2_CTRL_CLASS_DETECT``
426      - 0xa30000
427      - The class containing motion or object detection controls. These controls
428        are described in :ref:`detect-controls`.
429    * - ``V4L2_CTRL_CLASS_CODEC_STATELESS``
430      - 0xa40000
431      - The class containing stateless codec controls. These controls are
432	described in :ref:`codec-stateless-controls`.
433    * - ``V4L2_CTRL_CLASS_COLORIMETRY``
434      - 0xa50000
435      - The class containing colorimetry controls. These controls are
436	described in :ref:`colorimetry-controls`.
437
438Return Value
439============
440
441On success 0 is returned, on error -1 and the ``errno`` variable is set
442appropriately. The generic error codes are described at the
443:ref:`Generic Error Codes <gen-errors>` chapter.
444
445EINVAL
446    The struct :c:type:`v4l2_ext_control` ``id`` is
447    invalid, or the struct :c:type:`v4l2_ext_controls`
448    ``which`` is invalid, or the struct
449    :c:type:`v4l2_ext_control` ``value`` was
450    inappropriate (e.g. the given menu index is not supported by the
451    driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL``
452    but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL``
453    is not supported by the kernel.
454    This error code is also returned by the
455    :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
456    more control values are in conflict.
457
458ERANGE
459    The struct :c:type:`v4l2_ext_control` ``value``
460    is out of bounds.
461
462EBUSY
463    The control is temporarily not changeable, possibly because another
464    applications took over control of the device function this control
465    belongs to, or (if the ``which`` field was set to
466    ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet
467    completed.
468
469ENOSPC
470    The space reserved for the control's payload is insufficient. The
471    field ``size`` is set to a value that is enough to store the payload
472    and this error code is returned.
473
474EACCES
475    Attempt to try or set a read-only control, or to get a write-only
476    control, or to get a control from a request that has not yet been
477    completed.
478
479    Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
480    device does not support requests.
481
482    Or if there is an attempt to set an inactive control and the driver is
483    not capable of caching the new value until the control is active again.
484