1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _VIDIOC_G_EXT_CTRLS: 4 .. _VIDIOC_G_EXT_CTRLS:
5 5
6 ********************************************** 6 ******************************************************************
7 ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, 7 ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
8 ********************************************** 8 ******************************************************************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDI 13 VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_G_EXT_CTRLS 18 .. c:macro:: VIDIOC_G_EXT_CTRLS
19 19
20 ``int ioctl(int fd, VIDIOC_G_EXT_CTRLS, struct 20 ``int ioctl(int fd, VIDIOC_G_EXT_CTRLS, struct v4l2_ext_controls *argp)``
21 21
22 .. c:macro:: VIDIOC_S_EXT_CTRLS 22 .. c:macro:: VIDIOC_S_EXT_CTRLS
23 23
24 ``int ioctl(int fd, VIDIOC_S_EXT_CTRLS, struct 24 ``int ioctl(int fd, VIDIOC_S_EXT_CTRLS, struct v4l2_ext_controls *argp)``
25 25
26 .. c:macro:: VIDIOC_TRY_EXT_CTRLS 26 .. c:macro:: VIDIOC_TRY_EXT_CTRLS
27 27
28 ``int ioctl(int fd, VIDIOC_TRY_EXT_CTRLS, stru 28 ``int ioctl(int fd, VIDIOC_TRY_EXT_CTRLS, struct v4l2_ext_controls *argp)``
29 29
30 Arguments 30 Arguments
31 ========= 31 =========
32 32
33 ``fd`` 33 ``fd``
34 File descriptor returned by :c:func:`open( 34 File descriptor returned by :c:func:`open()`.
35 35
36 ``argp`` 36 ``argp``
37 Pointer to struct :c:type:`v4l2_ext_contro 37 Pointer to struct :c:type:`v4l2_ext_controls`.
38 38
39 Description 39 Description
40 =========== 40 ===========
41 41
42 These ioctls allow the caller to get or set mu 42 These ioctls allow the caller to get or set multiple controls
43 atomically. Control IDs are grouped into contr 43 atomically. Control IDs are grouped into control classes (see
44 :ref:`ctrl-class`) and all controls in the con 44 :ref:`ctrl-class`) and all controls in the control array must belong
45 to the same control class. 45 to the same control class.
46 46
47 Applications must always fill in the ``count`` 47 Applications must always fill in the ``count``, ``which``, ``controls``
48 and ``reserved`` fields of struct 48 and ``reserved`` fields of struct
49 :c:type:`v4l2_ext_controls`, and initialize th 49 :c:type:`v4l2_ext_controls`, and initialize the
50 struct :c:type:`v4l2_ext_control` array pointe 50 struct :c:type:`v4l2_ext_control` array pointed to
51 by the ``controls`` fields. 51 by the ``controls`` fields.
52 52
53 To get the current value of a set of controls 53 To get the current value of a set of controls applications initialize
54 the ``id``, ``size`` and ``reserved2`` fields 54 the ``id``, ``size`` and ``reserved2`` fields of each struct
55 :c:type:`v4l2_ext_control` and call the 55 :c:type:`v4l2_ext_control` and call the
56 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` 56 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls must also set the
57 ``string`` field. Controls of compound types 57 ``string`` field. Controls of compound types
58 (``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must s 58 (``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
59 59
60 If the ``size`` is too small to receive the co 60 If the ``size`` is too small to receive the control result (only
61 relevant for pointer-type controls like string 61 relevant for pointer-type controls like strings), then the driver will
62 set ``size`` to a valid value and return an `` 62 set ``size`` to a valid value and return an ``ENOSPC`` error code. You
63 should re-allocate the memory to this new size 63 should re-allocate the memory to this new size and try again. For the
64 string type it is possible that the same issue 64 string type it is possible that the same issue occurs again if the
65 string has grown in the meantime. It is recomm 65 string has grown in the meantime. It is recommended to call
66 :ref:`VIDIOC_QUERYCTRL` first and use 66 :ref:`VIDIOC_QUERYCTRL` first and use
67 ``maximum``\ +1 as the new ``size`` value. It 67 ``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is
68 sufficient memory. 68 sufficient memory.
69 69
70 N-dimensional arrays are set and retrieved row 70 N-dimensional arrays are set and retrieved row-by-row. You cannot set a
71 partial array, all elements have to be set or 71 partial array, all elements have to be set or retrieved. The total size
72 is calculated as ``elems`` * ``elem_size``. Th 72 is calculated as ``elems`` * ``elem_size``. These values can be obtained
73 by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC 73 by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
74 74
75 To change the value of a set of controls appli 75 To change the value of a set of controls applications initialize the
76 ``id``, ``size``, ``reserved2`` and ``value/va 76 ``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
77 of each struct :c:type:`v4l2_ext_control` and 77 of each struct :c:type:`v4l2_ext_control` and call
78 the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTR 78 the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
79 control values are valid. 79 control values are valid.
80 80
81 To check if a set of controls have correct val 81 To check if a set of controls have correct values applications
82 initialize the ``id``, ``size``, ``reserved2`` 82 initialize the ``id``, ``size``, ``reserved2`` and
83 ``value/value64/string/ptr`` fields of each st 83 ``value/value64/string/ptr`` fields of each struct
84 :c:type:`v4l2_ext_control` and call the 84 :c:type:`v4l2_ext_control` and call the
85 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS 85 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
86 values are automatically adjusted to a valid v 86 values are automatically adjusted to a valid value or if an error is
87 returned. 87 returned.
88 88
89 When the ``id`` or ``which`` is invalid driver 89 When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error
90 code. When the value is out of bounds drivers 90 code. When the value is out of bounds drivers can choose to take the
91 closest valid value or return an ``ERANGE`` er 91 closest valid value or return an ``ERANGE`` error code, whatever seems more
92 appropriate. In the first case the new value i 92 appropriate. In the first case the new value is set in struct
93 :c:type:`v4l2_ext_control`. If the new control 93 :c:type:`v4l2_ext_control`. If the new control value
94 is inappropriate (e.g. the given menu index is 94 is inappropriate (e.g. the given menu index is not supported by the menu
95 control), then this will also result in an ``E 95 control), then this will also result in an ``EINVAL`` error code error.
96 96
97 If ``request_fd`` is set to a not-yet-queued : 97 If ``request_fd`` is set to a not-yet-queued :ref:`request <media-request-api>`
98 file descriptor and ``which`` is set to ``V4L2 98 file descriptor and ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``,
99 then the controls are not applied immediately 99 then the controls are not applied immediately when calling
100 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` 100 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, but instead are applied by
101 the driver for the buffer associated with the 101 the driver for the buffer associated with the same request.
102 If the device does not support requests, then 102 If the device does not support requests, then ``EACCES`` will be returned.
103 If requests are supported but an invalid reque 103 If requests are supported but an invalid request file descriptor is given,
104 then ``EINVAL`` will be returned. 104 then ``EINVAL`` will be returned.
105 105
106 An attempt to call :ref:`VIDIOC_S_EXT_CTRLS <V 106 An attempt to call :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` for a
107 request that has already been queued will resu 107 request that has already been queued will result in an ``EBUSY`` error.
108 108
109 If ``request_fd`` is specified and ``which`` i 109 If ``request_fd`` is specified and ``which`` is set to
110 ``V4L2_CTRL_WHICH_REQUEST_VAL`` during a call 110 ``V4L2_CTRL_WHICH_REQUEST_VAL`` during a call to
111 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` 111 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then it will return the
112 values of the controls at the time of request 112 values of the controls at the time of request completion.
113 If the request is not yet completed, then this 113 If the request is not yet completed, then this will result in an
114 ``EACCES`` error. 114 ``EACCES`` error.
115 115
116 The driver will only set/get these controls if 116 The driver will only set/get these controls if all control values are
117 correct. This prevents the situation where onl 117 correct. This prevents the situation where only some of the controls
118 were set/get. Only low-level errors (e. g. a f 118 were set/get. Only low-level errors (e. g. a failed i2c command) can
119 still cause this situation. 119 still cause this situation.
120 120
121 .. tabularcolumns:: |p{6.8cm}|p{4.0cm}|p{6.5cm 121 .. tabularcolumns:: |p{6.8cm}|p{4.0cm}|p{6.5cm}|
122 122
123 .. c:type:: v4l2_ext_control 123 .. c:type:: v4l2_ext_control
124 124
125 .. raw:: latex 125 .. raw:: latex
126 126
127 \footnotesize 127 \footnotesize
128 128
129 .. cssclass:: longtable 129 .. cssclass:: longtable
130 130
131 .. flat-table:: struct v4l2_ext_control 131 .. flat-table:: struct v4l2_ext_control
132 :header-rows: 0 132 :header-rows: 0
133 :stub-columns: 0 133 :stub-columns: 0
134 :widths: 1 1 2 134 :widths: 1 1 2
135 135
136 * - __u32 136 * - __u32
137 - ``id`` 137 - ``id``
138 - Identifies the control, set by the app 138 - Identifies the control, set by the application.
139 * - __u32 139 * - __u32
140 - ``size`` 140 - ``size``
141 - The total size in bytes of the payload 141 - The total size in bytes of the payload of this control.
142 * - :cspan:`2` The ``size`` field is norma 142 * - :cspan:`2` The ``size`` field is normally 0, but for pointer
143 controls this should be set to the siz 143 controls this should be set to the size of the memory that contains
144 the payload or that will receive the p 144 the payload or that will receive the payload.
145 If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_ 145 If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value
146 is less than is required to store the 146 is less than is required to store the payload result, then it is set
147 to a value large enough to store the p 147 to a value large enough to store the payload result and ``ENOSPC`` is
148 returned. 148 returned.
149 149
150 .. note:: 150 .. note::
151 151
152 For string controls, this ``size`` 152 For string controls, this ``size`` field should
153 not be confused with the length of 153 not be confused with the length of the string. This field refers
154 to the size of the memory that cont 154 to the size of the memory that contains the string. The actual
155 *length* of the string may well be 155 *length* of the string may well be much smaller.
156 * - __u32 156 * - __u32
157 - ``reserved2``\ [1] 157 - ``reserved2``\ [1]
158 - Reserved for future extensions. Driver 158 - Reserved for future extensions. Drivers and applications must set
159 the array to zero. 159 the array to zero.
160 * - union { 160 * - union {
161 - (anonymous) 161 - (anonymous)
162 * - __s32 162 * - __s32
163 - ``value`` 163 - ``value``
164 - New value or current value. Valid if t 164 - New value or current value. Valid if this control is not of type
165 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L 165 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
166 not set. 166 not set.
167 * - __s64 167 * - __s64
168 - ``value64`` 168 - ``value64``
169 - New value or current value. Valid if t 169 - New value or current value. Valid if this control is of type
170 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L 170 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
171 not set. 171 not set.
172 * - char * 172 * - char *
173 - ``string`` 173 - ``string``
174 - A pointer to a string. Valid if this c 174 - A pointer to a string. Valid if this control is of type
175 ``V4L2_CTRL_TYPE_STRING``. 175 ``V4L2_CTRL_TYPE_STRING``.
176 * - __u8 * 176 * - __u8 *
177 - ``p_u8`` 177 - ``p_u8``
178 - A pointer to a matrix control of unsig 178 - A pointer to a matrix control of unsigned 8-bit values. Valid if
179 this control is of type ``V4L2_CTRL_TY 179 this control is of type ``V4L2_CTRL_TYPE_U8``.
180 * - __u16 * 180 * - __u16 *
181 - ``p_u16`` 181 - ``p_u16``
182 - A pointer to a matrix control of unsig 182 - A pointer to a matrix control of unsigned 16-bit values. Valid if
183 this control is of type ``V4L2_CTRL_TY 183 this control is of type ``V4L2_CTRL_TYPE_U16``.
184 * - __u32 * 184 * - __u32 *
185 - ``p_u32`` 185 - ``p_u32``
186 - A pointer to a matrix control of unsig 186 - A pointer to a matrix control of unsigned 32-bit values. Valid if
187 this control is of type ``V4L2_CTRL_TY 187 this control is of type ``V4L2_CTRL_TYPE_U32``.
188 * - __s32 * 188 * - __s32 *
189 - ``p_s32`` 189 - ``p_s32``
190 - A pointer to a matrix control of signe 190 - A pointer to a matrix control of signed 32-bit values. Valid if
191 this control is of type ``V4L2_CTRL_TY 191 this control is of type ``V4L2_CTRL_TYPE_INTEGER`` and
192 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set. 192 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set.
193 * - __s64 * 193 * - __s64 *
194 - ``p_s64`` 194 - ``p_s64``
195 - A pointer to a matrix control of signe 195 - A pointer to a matrix control of signed 64-bit values. Valid if
196 this control is of type ``V4L2_CTRL_TY 196 this control is of type ``V4L2_CTRL_TYPE_INTEGER64`` and
197 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set. 197 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set.
198 * - struct :c:type:`v4l2_area` * 198 * - struct :c:type:`v4l2_area` *
199 - ``p_area`` 199 - ``p_area``
200 - A pointer to a struct :c:type:`v4l2_ar 200 - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
201 of type ``V4L2_CTRL_TYPE_AREA``. 201 of type ``V4L2_CTRL_TYPE_AREA``.
202 * - struct :c:type:`v4l2_ctrl_h264_sps` * 202 * - struct :c:type:`v4l2_ctrl_h264_sps` *
203 - ``p_h264_sps`` 203 - ``p_h264_sps``
204 - A pointer to a struct :c:type:`v4l2_ct 204 - A pointer to a struct :c:type:`v4l2_ctrl_h264_sps`. Valid if this control is
205 of type ``V4L2_CTRL_TYPE_H264_SPS``. 205 of type ``V4L2_CTRL_TYPE_H264_SPS``.
206 * - struct :c:type:`v4l2_ctrl_h264_pps` * 206 * - struct :c:type:`v4l2_ctrl_h264_pps` *
207 - ``p_h264_pps`` 207 - ``p_h264_pps``
208 - A pointer to a struct :c:type:`v4l2_ct 208 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pps`. Valid if this control is
209 of type ``V4L2_CTRL_TYPE_H264_PPS``. 209 of type ``V4L2_CTRL_TYPE_H264_PPS``.
210 * - struct :c:type:`v4l2_ctrl_h264_scaling 210 * - struct :c:type:`v4l2_ctrl_h264_scaling_matrix` *
211 - ``p_h264_scaling_matrix`` 211 - ``p_h264_scaling_matrix``
212 - A pointer to a struct :c:type:`v4l2_ct 212 - A pointer to a struct :c:type:`v4l2_ctrl_h264_scaling_matrix`. Valid if this control is
213 of type ``V4L2_CTRL_TYPE_H264_SCALING_ 213 of type ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX``.
214 * - struct :c:type:`v4l2_ctrl_h264_pred_we 214 * - struct :c:type:`v4l2_ctrl_h264_pred_weights` *
215 - ``p_h264_pred_weights`` 215 - ``p_h264_pred_weights``
216 - A pointer to a struct :c:type:`v4l2_ct 216 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pred_weights`. Valid if this control is
217 of type ``V4L2_CTRL_TYPE_H264_PRED_WEI 217 of type ``V4L2_CTRL_TYPE_H264_PRED_WEIGHTS``.
218 * - struct :c:type:`v4l2_ctrl_h264_slice_p 218 * - struct :c:type:`v4l2_ctrl_h264_slice_params` *
219 - ``p_h264_slice_params`` 219 - ``p_h264_slice_params``
220 - A pointer to a struct :c:type:`v4l2_ct 220 - A pointer to a struct :c:type:`v4l2_ctrl_h264_slice_params`. Valid if this control is
221 of type ``V4L2_CTRL_TYPE_H264_SLICE_PA 221 of type ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS``.
222 * - struct :c:type:`v4l2_ctrl_h264_decode_ 222 * - struct :c:type:`v4l2_ctrl_h264_decode_params` *
223 - ``p_h264_decode_params`` 223 - ``p_h264_decode_params``
224 - A pointer to a struct :c:type:`v4l2_ct 224 - A pointer to a struct :c:type:`v4l2_ctrl_h264_decode_params`. Valid if this control is
225 of type ``V4L2_CTRL_TYPE_H264_DECODE_P 225 of type ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS``.
226 * - struct :c:type:`v4l2_ctrl_fwht_params` 226 * - struct :c:type:`v4l2_ctrl_fwht_params` *
227 - ``p_fwht_params`` 227 - ``p_fwht_params``
228 - A pointer to a struct :c:type:`v4l2_ct 228 - A pointer to a struct :c:type:`v4l2_ctrl_fwht_params`. Valid if this control is
229 of type ``V4L2_CTRL_TYPE_FWHT_PARAMS`` 229 of type ``V4L2_CTRL_TYPE_FWHT_PARAMS``.
230 * - struct :c:type:`v4l2_ctrl_vp8_frame` * 230 * - struct :c:type:`v4l2_ctrl_vp8_frame` *
231 - ``p_vp8_frame`` 231 - ``p_vp8_frame``
232 - A pointer to a struct :c:type:`v4l2_ct 232 - A pointer to a struct :c:type:`v4l2_ctrl_vp8_frame`. Valid if this control is
233 of type ``V4L2_CTRL_TYPE_VP8_FRAME``. 233 of type ``V4L2_CTRL_TYPE_VP8_FRAME``.
234 * - struct :c:type:`v4l2_ctrl_mpeg2_sequen 234 * - struct :c:type:`v4l2_ctrl_mpeg2_sequence` *
235 - ``p_mpeg2_sequence`` 235 - ``p_mpeg2_sequence``
236 - A pointer to a struct :c:type:`v4l2_ct 236 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_sequence`. Valid if this control is
237 of type ``V4L2_CTRL_TYPE_MPEG2_SEQUENC 237 of type ``V4L2_CTRL_TYPE_MPEG2_SEQUENCE``.
238 * - struct :c:type:`v4l2_ctrl_mpeg2_pictur 238 * - struct :c:type:`v4l2_ctrl_mpeg2_picture` *
239 - ``p_mpeg2_picture`` 239 - ``p_mpeg2_picture``
240 - A pointer to a struct :c:type:`v4l2_ct 240 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_picture`. Valid if this control is
241 of type ``V4L2_CTRL_TYPE_MPEG2_PICTURE 241 of type ``V4L2_CTRL_TYPE_MPEG2_PICTURE``.
242 * - struct :c:type:`v4l2_ctrl_mpeg2_quanti 242 * - struct :c:type:`v4l2_ctrl_mpeg2_quantisation` *
243 - ``p_mpeg2_quantisation`` 243 - ``p_mpeg2_quantisation``
244 - A pointer to a struct :c:type:`v4l2_ct 244 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_quantisation`. Valid if this control is
245 of type ``V4L2_CTRL_TYPE_MPEG2_QUANTIS 245 of type ``V4L2_CTRL_TYPE_MPEG2_QUANTISATION``.
246 * - struct :c:type:`v4l2_ctrl_vp9_compress 246 * - struct :c:type:`v4l2_ctrl_vp9_compressed_hdr` *
247 - ``p_vp9_compressed_hdr_probs`` 247 - ``p_vp9_compressed_hdr_probs``
248 - A pointer to a struct :c:type:`v4l2_ct 248 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_compressed_hdr`. Valid if this
249 control is of type ``V4L2_CTRL_TYPE_VP 249 control is of type ``V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR``.
250 * - struct :c:type:`v4l2_ctrl_vp9_frame` * 250 * - struct :c:type:`v4l2_ctrl_vp9_frame` *
251 - ``p_vp9_frame`` 251 - ``p_vp9_frame``
252 - A pointer to a struct :c:type:`v4l2_ct 252 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_frame`. Valid if this
253 control is of type ``V4L2_CTRL_TYPE_VP 253 control is of type ``V4L2_CTRL_TYPE_VP9_FRAME``.
254 * - struct :c:type:`v4l2_ctrl_hdr10_cll_in 254 * - struct :c:type:`v4l2_ctrl_hdr10_cll_info` *
255 - ``p_hdr10_cll`` 255 - ``p_hdr10_cll``
256 - A pointer to a struct :c:type:`v4l2_ct 256 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_cll_info`. Valid if this control is
257 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INF 257 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INFO``.
258 * - struct :c:type:`v4l2_ctrl_hdr10_master 258 * - struct :c:type:`v4l2_ctrl_hdr10_mastering_display` *
259 - ``p_hdr10_mastering`` 259 - ``p_hdr10_mastering``
260 - A pointer to a struct :c:type:`v4l2_ct 260 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_mastering_display`. Valid if this control is
261 of type ``V4L2_CTRL_TYPE_HDR10_MASTERI 261 of type ``V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY``.
262 * - struct :c:type:`v4l2_ctrl_hevc_sps` * 262 * - struct :c:type:`v4l2_ctrl_hevc_sps` *
263 - ``p_hevc_sps`` 263 - ``p_hevc_sps``
264 - A pointer to a struct :c:type:`v4l2_ct 264 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_sps`. Valid if this
265 control is of type ``V4L2_CTRL_TYPE_HE 265 control is of type ``V4L2_CTRL_TYPE_HEVC_SPS``.
266 * - struct :c:type:`v4l2_ctrl_hevc_pps` * 266 * - struct :c:type:`v4l2_ctrl_hevc_pps` *
267 - ``p_hevc_pps`` 267 - ``p_hevc_pps``
268 - A pointer to a struct :c:type:`v4l2_ct 268 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_pps`. Valid if this
269 control is of type ``V4L2_CTRL_TYPE_HE 269 control is of type ``V4L2_CTRL_TYPE_HEVC_PPS``.
270 * - struct :c:type:`v4l2_ctrl_hevc_slice_p 270 * - struct :c:type:`v4l2_ctrl_hevc_slice_params` *
271 - ``p_hevc_slice_params`` 271 - ``p_hevc_slice_params``
272 - A pointer to a struct :c:type:`v4l2_ct 272 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_slice_params`. Valid if this
273 control is of type ``V4L2_CTRL_TYPE_HE 273 control is of type ``V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS``.
274 * - struct :c:type:`v4l2_ctrl_hevc_scaling 274 * - struct :c:type:`v4l2_ctrl_hevc_scaling_matrix` *
275 - ``p_hevc_scaling_matrix`` 275 - ``p_hevc_scaling_matrix``
276 - A pointer to a struct :c:type:`v4l2_ct 276 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_scaling_matrix`. Valid if this
277 control is of type ``V4L2_CTRL_TYPE_HE 277 control is of type ``V4L2_CTRL_TYPE_HEVC_SCALING_MATRIX``.
278 * - struct :c:type:`v4l2_ctrl_hevc_decode_ 278 * - struct :c:type:`v4l2_ctrl_hevc_decode_params` *
279 - ``p_hevc_decode_params`` 279 - ``p_hevc_decode_params``
280 - A pointer to a struct :c:type:`v4l2_ct 280 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_decode_params`. Valid if this
281 control is of type ``V4L2_CTRL_TYPE_HE 281 control is of type ``V4L2_CTRL_TYPE_HEVC_DECODE_PARAMS``.
282 * - struct :c:type:`v4l2_ctrl_av1_sequence 282 * - struct :c:type:`v4l2_ctrl_av1_sequence` *
283 - ``p_av1_sequence`` 283 - ``p_av1_sequence``
284 - A pointer to a struct :c:type:`v4l2_ct 284 - A pointer to a struct :c:type:`v4l2_ctrl_av1_sequence`. Valid if this control is
285 of type ``V4L2_CTRL_TYPE_AV1_SEQUENCE` 285 of type ``V4L2_CTRL_TYPE_AV1_SEQUENCE``.
286 * - struct :c:type:`v4l2_ctrl_av1_tile_gro 286 * - struct :c:type:`v4l2_ctrl_av1_tile_group_entry` *
287 - ``p_av1_tile_group_entry`` 287 - ``p_av1_tile_group_entry``
288 - A pointer to a struct :c:type:`v4l2_ct 288 - A pointer to a struct :c:type:`v4l2_ctrl_av1_tile_group_entry`. Valid if this control is
289 of type ``V4L2_CTRL_TYPE_AV1_TILE_GROU 289 of type ``V4L2_CTRL_TYPE_AV1_TILE_GROUP_ENTRY``.
290 * - struct :c:type:`v4l2_ctrl_av1_frame` * 290 * - struct :c:type:`v4l2_ctrl_av1_frame` *
291 - ``p_av1_frame`` 291 - ``p_av1_frame``
292 - A pointer to a struct :c:type:`v4l2_ct 292 - A pointer to a struct :c:type:`v4l2_ctrl_av1_frame`. Valid if this control is
293 of type ``V4L2_CTRL_TYPE_AV1_FRAME``. 293 of type ``V4L2_CTRL_TYPE_AV1_FRAME``.
294 * - struct :c:type:`v4l2_ctrl_av1_film_gra 294 * - struct :c:type:`v4l2_ctrl_av1_film_grain` *
295 - ``p_av1_film_grain`` 295 - ``p_av1_film_grain``
296 - A pointer to a struct :c:type:`v4l2_ct 296 - A pointer to a struct :c:type:`v4l2_ctrl_av1_film_grain`. Valid if this control is
297 of type ``V4L2_CTRL_TYPE_AV1_FILM_GRAI 297 of type ``V4L2_CTRL_TYPE_AV1_FILM_GRAIN``.
298 * - struct :c:type:`v4l2_ctrl_hdr10_cll_in 298 * - struct :c:type:`v4l2_ctrl_hdr10_cll_info` *
299 - ``p_hdr10_cll_info`` 299 - ``p_hdr10_cll_info``
300 - A pointer to a struct :c:type:`v4l2_ct 300 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_cll_info`. Valid if this control is
301 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INF 301 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INFO``.
302 * - struct :c:type:`v4l2_ctrl_hdr10_master 302 * - struct :c:type:`v4l2_ctrl_hdr10_mastering_display` *
303 - ``p_hdr10_mastering_display`` 303 - ``p_hdr10_mastering_display``
304 - A pointer to a struct :c:type:`v4l2_ct 304 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_mastering_display`. Valid if this control is
305 of type ``V4L2_CTRL_TYPE_HDR10_MASTERI 305 of type ``V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY``.
306 * - void * 306 * - void *
307 - ``ptr`` 307 - ``ptr``
308 - A pointer to a compound type which can 308 - A pointer to a compound type which can be an N-dimensional array
309 and/or a compound type (the control's 309 and/or a compound type (the control's type is >=
310 ``V4L2_CTRL_COMPOUND_TYPES``). Valid i 310 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
311 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set 311 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
312 * - } 312 * - }
313 - 313 -
314 314
315 .. raw:: latex 315 .. raw:: latex
316 316
317 \normalsize 317 \normalsize
318 318
319 .. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8c 319 .. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8cm}|
320 320
321 .. c:type:: v4l2_ext_controls 321 .. c:type:: v4l2_ext_controls
322 322
323 .. cssclass:: longtable 323 .. cssclass:: longtable
324 324
325 .. flat-table:: struct v4l2_ext_controls 325 .. flat-table:: struct v4l2_ext_controls
326 :header-rows: 0 326 :header-rows: 0
327 :stub-columns: 0 327 :stub-columns: 0
328 :widths: 1 1 2 328 :widths: 1 1 2
329 329
330 * - union { 330 * - union {
331 - (anonymous) 331 - (anonymous)
332 * - __u32 332 * - __u32
333 - ``which`` 333 - ``which``
334 - Which value of the control to get/set/ 334 - Which value of the control to get/set/try.
335 * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` 335 * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
336 the control, ``V4L2_CTRL_WHICH_DEF_VAL 336 the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
337 value of the control and ``V4L2_CTRL_W 337 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
338 these controls have to be retrieved fr 338 these controls have to be retrieved from a request or tried/set for
339 a request. In the latter case the ``re 339 a request. In the latter case the ``request_fd`` field contains the
340 file descriptor of the request that sh 340 file descriptor of the request that should be used. If the device
341 does not support requests, then ``EACC 341 does not support requests, then ``EACCES`` will be returned.
342 342
343 When using ``V4L2_CTRL_WHICH_DEF_VAL`` 343 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
344 get the default value of the control, 344 get the default value of the control, you cannot set or try it.
345 345
346 For backwards compatibility you can al 346 For backwards compatibility you can also use a control class here
347 (see :ref:`ctrl-class`). In that case 347 (see :ref:`ctrl-class`). In that case all controls have to
348 belong to that control class. This usa 348 belong to that control class. This usage is deprecated, instead
349 just use ``V4L2_CTRL_WHICH_CUR_VAL``. 349 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
350 drivers that do not yet support ``V4L2 350 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
351 that require a control class here. You 351 that require a control class here. You can test for such drivers
352 by setting ``which`` to ``V4L2_CTRL_WH 352 by setting ``which`` to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
353 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_E 353 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a count of 0.
354 If that fails, then the driver does no 354 If that fails, then the driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
355 * - __u32 355 * - __u32
356 - ``ctrl_class`` 356 - ``ctrl_class``
357 - Deprecated name kept for backwards com 357 - Deprecated name kept for backwards compatibility. Use ``which`` instead.
358 * - } 358 * - }
359 - 359 -
360 * - __u32 360 * - __u32
361 - ``count`` 361 - ``count``
362 - The number of controls in the controls 362 - The number of controls in the controls array. May also be zero.
363 * - __u32 363 * - __u32
364 - ``error_idx`` 364 - ``error_idx``
365 - Index of the failing control. Set by t 365 - Index of the failing control. Set by the driver in case of an error.
366 * - :cspan:`2` If the error is associated 366 * - :cspan:`2` If the error is associated
367 with a particular control, then ``erro 367 with a particular control, then ``error_idx`` is set to the index
368 of that control. If the error is not r 368 of that control. If the error is not related to a specific
369 control, or the validation step failed 369 control, or the validation step failed (see below), then
370 ``error_idx`` is set to ``count``. The 370 ``error_idx`` is set to ``count``. The value is undefined if the
371 ioctl returned 0 (success). 371 ioctl returned 0 (success).
372 372
373 Before controls are read from/written 373 Before controls are read from/written to hardware a validation
374 step takes place: this checks if all c 374 step takes place: this checks if all controls in the list are
375 valid controls, if no attempt is made 375 valid controls, if no attempt is made to write to a read-only
376 control or read from a write-only cont 376 control or read from a write-only control, and any other up-front
377 checks that can be done without access 377 checks that can be done without accessing the hardware. The exact
378 validations done during this step are 378 validations done during this step are driver dependent since some
379 checks might require hardware access f 379 checks might require hardware access for some devices, thus making
380 it impossible to do those checks up-fr 380 it impossible to do those checks up-front. However, drivers should
381 make a best-effort to do as many up-fr 381 make a best-effort to do as many up-front checks as possible.
382 382
383 This check is done to avoid leaving th 383 This check is done to avoid leaving the hardware in an
384 inconsistent state due to easy-to-avoi 384 inconsistent state due to easy-to-avoid problems. But it leads to
385 another problem: the application needs 385 another problem: the application needs to know whether an error
386 came from the validation step (meaning 386 came from the validation step (meaning that the hardware was not
387 touched) or from an error during the a 387 touched) or from an error during the actual reading from/writing
388 to hardware. 388 to hardware.
389 389
390 The, in hindsight quite poor, solution 390 The, in hindsight quite poor, solution for that is to set
391 ``error_idx`` to ``count`` if the vali 391 ``error_idx`` to ``count`` if the validation failed. This has the
392 unfortunate side-effect that it is not 392 unfortunate side-effect that it is not possible to see which
393 control failed the validation. If the 393 control failed the validation. If the validation was successful
394 and the error happened while accessing 394 and the error happened while accessing the hardware, then
395 ``error_idx`` is less than ``count`` a 395 ``error_idx`` is less than ``count`` and only the controls up to
396 ``error_idx-1`` were read or written c 396 ``error_idx-1`` were read or written correctly, and the state of
397 the remaining controls is undefined. 397 the remaining controls is undefined.
398 398
399 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDI 399 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
400 also no need to handle the validation 400 also no need to handle the validation step in this special way, so
401 ``error_idx`` will just be set to the 401 ``error_idx`` will just be set to the control that failed the
402 validation step instead of to ``count` 402 validation step instead of to ``count``. This means that if
403 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT 403 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
404 then you can call :ref:`VIDIOC_TRY_EXT 404 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
405 actual control that failed the validat 405 actual control that failed the validation step. Unfortunately,
406 there is no ``TRY`` equivalent for :re 406 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
407 * - __s32 407 * - __s32
408 - ``request_fd`` 408 - ``request_fd``
409 - File descriptor of the request to be u 409 - File descriptor of the request to be used by this operation. Only
410 valid if ``which`` is set to ``V4L2_CT 410 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``.
411 If the device does not support request 411 If the device does not support requests, then ``EACCES`` will be returned.
412 If requests are supported but an inval 412 If requests are supported but an invalid request file descriptor is
413 given, then ``EINVAL`` will be returne 413 given, then ``EINVAL`` will be returned.
414 * - __u32 414 * - __u32
415 - ``reserved``\ [1] 415 - ``reserved``\ [1]
416 - Reserved for future extensions. 416 - Reserved for future extensions.
417 417
418 Drivers and applications must set the 418 Drivers and applications must set the array to zero.
419 * - struct :c:type:`v4l2_ext_control` * 419 * - struct :c:type:`v4l2_ext_control` *
420 - ``controls`` 420 - ``controls``
421 - Pointer to an array of ``count`` v4l2_ 421 - Pointer to an array of ``count`` v4l2_ext_control structures.
422 422
423 Ignored if ``count`` equals zero. 423 Ignored if ``count`` equals zero.
424 424
425 .. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm 425 .. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm}|
426 426
427 .. cssclass:: longtable 427 .. cssclass:: longtable
428 428
429 .. _ctrl-class: 429 .. _ctrl-class:
430 430
431 .. flat-table:: Control classes 431 .. flat-table:: Control classes
432 :header-rows: 0 432 :header-rows: 0
433 :stub-columns: 0 433 :stub-columns: 0
434 :widths: 3 1 4 434 :widths: 3 1 4
435 435
436 * - ``V4L2_CTRL_CLASS_USER`` 436 * - ``V4L2_CTRL_CLASS_USER``
437 - 0x980000 437 - 0x980000
438 - The class containing user controls. Th 438 - The class containing user controls. These controls are described
439 in :ref:`control`. All controls that c 439 in :ref:`control`. All controls that can be set using the
440 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` a 440 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
441 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` i 441 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
442 class. 442 class.
443 * - ``V4L2_CTRL_CLASS_CODEC`` 443 * - ``V4L2_CTRL_CLASS_CODEC``
444 - 0x990000 444 - 0x990000
445 - The class containing stateful codec co 445 - The class containing stateful codec controls. These controls are
446 described in :ref:`codec-controls`. 446 described in :ref:`codec-controls`.
447 * - ``V4L2_CTRL_CLASS_CAMERA`` 447 * - ``V4L2_CTRL_CLASS_CAMERA``
448 - 0x9a0000 448 - 0x9a0000
449 - The class containing camera controls. 449 - The class containing camera controls. These controls are described
450 in :ref:`camera-controls`. 450 in :ref:`camera-controls`.
451 * - ``V4L2_CTRL_CLASS_FM_TX`` 451 * - ``V4L2_CTRL_CLASS_FM_TX``
452 - 0x9b0000 452 - 0x9b0000
453 - The class containing FM Transmitter (F 453 - The class containing FM Transmitter (FM TX) controls. These
454 controls are described in :ref:`fm-tx- 454 controls are described in :ref:`fm-tx-controls`.
455 * - ``V4L2_CTRL_CLASS_FLASH`` 455 * - ``V4L2_CTRL_CLASS_FLASH``
456 - 0x9c0000 456 - 0x9c0000
457 - The class containing flash device cont 457 - The class containing flash device controls. These controls are
458 described in :ref:`flash-controls`. 458 described in :ref:`flash-controls`.
459 * - ``V4L2_CTRL_CLASS_JPEG`` 459 * - ``V4L2_CTRL_CLASS_JPEG``
460 - 0x9d0000 460 - 0x9d0000
461 - The class containing JPEG compression 461 - The class containing JPEG compression controls. These controls are
462 described in :ref:`jpeg-controls`. 462 described in :ref:`jpeg-controls`.
463 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` 463 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
464 - 0x9e0000 464 - 0x9e0000
465 - The class containing image source cont 465 - The class containing image source controls. These controls are
466 described in :ref:`image-source-contro 466 described in :ref:`image-source-controls`.
467 * - ``V4L2_CTRL_CLASS_IMAGE_PROC`` 467 * - ``V4L2_CTRL_CLASS_IMAGE_PROC``
468 - 0x9f0000 468 - 0x9f0000
469 - The class containing image processing 469 - The class containing image processing controls. These controls are
470 described in :ref:`image-process-contr 470 described in :ref:`image-process-controls`.
471 * - ``V4L2_CTRL_CLASS_FM_RX`` 471 * - ``V4L2_CTRL_CLASS_FM_RX``
472 - 0xa10000 472 - 0xa10000
473 - The class containing FM Receiver (FM R 473 - The class containing FM Receiver (FM RX) controls. These controls
474 are described in :ref:`fm-rx-controls` 474 are described in :ref:`fm-rx-controls`.
475 * - ``V4L2_CTRL_CLASS_RF_TUNER`` 475 * - ``V4L2_CTRL_CLASS_RF_TUNER``
476 - 0xa20000 476 - 0xa20000
477 - The class containing RF tuner controls 477 - The class containing RF tuner controls. These controls are
478 described in :ref:`rf-tuner-controls`. 478 described in :ref:`rf-tuner-controls`.
479 * - ``V4L2_CTRL_CLASS_DETECT`` 479 * - ``V4L2_CTRL_CLASS_DETECT``
480 - 0xa30000 480 - 0xa30000
481 - The class containing motion or object 481 - The class containing motion or object detection controls. These controls
482 are described in :ref:`detect-controls 482 are described in :ref:`detect-controls`.
483 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS`` 483 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS``
484 - 0xa40000 484 - 0xa40000
485 - The class containing stateless codec c 485 - The class containing stateless codec controls. These controls are
486 described in :ref:`codec-stateless-con 486 described in :ref:`codec-stateless-controls`.
487 * - ``V4L2_CTRL_CLASS_COLORIMETRY`` 487 * - ``V4L2_CTRL_CLASS_COLORIMETRY``
488 - 0xa50000 488 - 0xa50000
489 - The class containing colorimetry contr 489 - The class containing colorimetry controls. These controls are
490 described in :ref:`colorimetry-control 490 described in :ref:`colorimetry-controls`.
491 491
492 Return Value 492 Return Value
493 ============ 493 ============
494 494
495 On success 0 is returned, on error -1 and the 495 On success 0 is returned, on error -1 and the ``errno`` variable is set
496 appropriately. The generic error codes are des 496 appropriately. The generic error codes are described at the
497 :ref:`Generic Error Codes <gen-errors>` chapte 497 :ref:`Generic Error Codes <gen-errors>` chapter.
498 498
499 EINVAL 499 EINVAL
500 The struct :c:type:`v4l2_ext_control` ``id 500 The struct :c:type:`v4l2_ext_control` ``id`` is
501 invalid, or the struct :c:type:`v4l2_ext_c 501 invalid, or the struct :c:type:`v4l2_ext_controls`
502 ``which`` is invalid, or the struct 502 ``which`` is invalid, or the struct
503 :c:type:`v4l2_ext_control` ``value`` was 503 :c:type:`v4l2_ext_control` ``value`` was
504 inappropriate (e.g. the given menu index i 504 inappropriate (e.g. the given menu index is not supported by the
505 driver), or the ``which`` field was set to 505 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL``
506 but the given ``request_fd`` was invalid o 506 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL``
507 is not supported by the kernel. 507 is not supported by the kernel.
508 This error code is also returned by the 508 This error code is also returned by the
509 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTR 509 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
510 more control values are in conflict. 510 more control values are in conflict.
511 511
512 ERANGE 512 ERANGE
513 The struct :c:type:`v4l2_ext_control` ``va 513 The struct :c:type:`v4l2_ext_control` ``value``
514 is out of bounds. 514 is out of bounds.
515 515
516 EBUSY 516 EBUSY
517 The control is temporarily not changeable, 517 The control is temporarily not changeable, possibly because another
518 applications took over control of the devi 518 applications took over control of the device function this control
519 belongs to, or (if the ``which`` field was 519 belongs to, or (if the ``which`` field was set to
520 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the reque 520 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet
521 completed. 521 completed.
522 522
523 ENOSPC 523 ENOSPC
524 The space reserved for the control's paylo 524 The space reserved for the control's payload is insufficient. The
525 field ``size`` is set to a value that is e 525 field ``size`` is set to a value that is enough to store the payload
526 and this error code is returned. 526 and this error code is returned.
527 527
528 EACCES 528 EACCES
529 Attempt to try or set a read-only control, 529 Attempt to try or set a read-only control, or to get a write-only
530 control, or to get a control from a reques 530 control, or to get a control from a request that has not yet been
531 completed. 531 completed.
532 532
533 Or the ``which`` field was set to ``V4L2_C 533 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
534 device does not support requests. 534 device does not support requests.
535 535
536 Or if there is an attempt to set an inacti 536 Or if there is an attempt to set an inactive control and the driver is
537 not capable of caching the new value until 537 not capable of caching the new value until the control is active again.
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