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 * - void * 225 - ``ptr`` 226 - A pointer to a compound type which can be an N-dimensional array 227 and/or a compound type (the control's type is >= 228 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if 229 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control. 230 * - } 231 - 232 233.. raw:: latex 234 235 \normalsize 236 237.. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8cm}| 238 239.. c:type:: v4l2_ext_controls 240 241.. cssclass:: longtable 242 243.. flat-table:: struct v4l2_ext_controls 244 :header-rows: 0 245 :stub-columns: 0 246 :widths: 1 1 2 247 248 * - union { 249 - (anonymous) 250 * - __u32 251 - ``which`` 252 - Which value of the control to get/set/try. 253 * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of 254 the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default 255 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that 256 these controls have to be retrieved from a request or tried/set for 257 a request. In the latter case the ``request_fd`` field contains the 258 file descriptor of the request that should be used. If the device 259 does not support requests, then ``EACCES`` will be returned. 260 261 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only 262 get the default value of the control, you cannot set or try it. 263 264 For backwards compatibility you can also use a control class here 265 (see :ref:`ctrl-class`). In that case all controls have to 266 belong to that control class. This usage is deprecated, instead 267 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old 268 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and 269 that require a control class here. You can test for such drivers 270 by setting ``which`` to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling 271 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a count of 0. 272 If that fails, then the driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``. 273 * - __u32 274 - ``ctrl_class`` 275 - Deprecated name kept for backwards compatibility. Use ``which`` instead. 276 * - } 277 - 278 * - __u32 279 - ``count`` 280 - The number of controls in the controls array. May also be zero. 281 * - __u32 282 - ``error_idx`` 283 - Index of the failing control. Set by the driver in case of an error. 284 * - :cspan:`2` If the error is associated 285 with a particular control, then ``error_idx`` is set to the index 286 of that control. If the error is not related to a specific 287 control, or the validation step failed (see below), then 288 ``error_idx`` is set to ``count``. The value is undefined if the 289 ioctl returned 0 (success). 290 291 Before controls are read from/written to hardware a validation 292 step takes place: this checks if all controls in the list are 293 valid controls, if no attempt is made to write to a read-only 294 control or read from a write-only control, and any other up-front 295 checks that can be done without accessing the hardware. The exact 296 validations done during this step are driver dependent since some 297 checks might require hardware access for some devices, thus making 298 it impossible to do those checks up-front. However, drivers should 299 make a best-effort to do as many up-front checks as possible. 300 301 This check is done to avoid leaving the hardware in an 302 inconsistent state due to easy-to-avoid problems. But it leads to 303 another problem: the application needs to know whether an error 304 came from the validation step (meaning that the hardware was not 305 touched) or from an error during the actual reading from/writing 306 to hardware. 307 308 The, in hindsight quite poor, solution for that is to set 309 ``error_idx`` to ``count`` if the validation failed. This has the 310 unfortunate side-effect that it is not possible to see which 311 control failed the validation. If the validation was successful 312 and the error happened while accessing the hardware, then 313 ``error_idx`` is less than ``count`` and only the controls up to 314 ``error_idx-1`` were read or written correctly, and the state of 315 the remaining controls is undefined. 316 317 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is 318 also no need to handle the validation step in this special way, so 319 ``error_idx`` will just be set to the control that failed the 320 validation step instead of to ``count``. This means that if 321 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``, 322 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the 323 actual control that failed the validation step. Unfortunately, 324 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. 325 * - __s32 326 - ``request_fd`` 327 - File descriptor of the request to be used by this operation. Only 328 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``. 329 If the device does not support requests, then ``EACCES`` will be returned. 330 If requests are supported but an invalid request file descriptor is 331 given, then ``EINVAL`` will be returned. 332 * - __u32 333 - ``reserved``\ [1] 334 - Reserved for future extensions. 335 336 Drivers and applications must set the array to zero. 337 * - struct :c:type:`v4l2_ext_control` * 338 - ``controls`` 339 - Pointer to an array of ``count`` v4l2_ext_control structures. 340 341 Ignored if ``count`` equals zero. 342 343.. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm}| 344 345.. cssclass:: longtable 346 347.. _ctrl-class: 348 349.. flat-table:: Control classes 350 :header-rows: 0 351 :stub-columns: 0 352 :widths: 3 1 4 353 354 * - ``V4L2_CTRL_CLASS_USER`` 355 - 0x980000 356 - The class containing user controls. These controls are described 357 in :ref:`control`. All controls that can be set using the 358 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and 359 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this 360 class. 361 * - ``V4L2_CTRL_CLASS_CODEC`` 362 - 0x990000 363 - The class containing stateful codec controls. These controls are 364 described in :ref:`codec-controls`. 365 * - ``V4L2_CTRL_CLASS_CAMERA`` 366 - 0x9a0000 367 - The class containing camera controls. These controls are described 368 in :ref:`camera-controls`. 369 * - ``V4L2_CTRL_CLASS_FM_TX`` 370 - 0x9b0000 371 - The class containing FM Transmitter (FM TX) controls. These 372 controls are described in :ref:`fm-tx-controls`. 373 * - ``V4L2_CTRL_CLASS_FLASH`` 374 - 0x9c0000 375 - The class containing flash device controls. These controls are 376 described in :ref:`flash-controls`. 377 * - ``V4L2_CTRL_CLASS_JPEG`` 378 - 0x9d0000 379 - The class containing JPEG compression controls. These controls are 380 described in :ref:`jpeg-controls`. 381 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` 382 - 0x9e0000 383 - The class containing image source controls. These controls are 384 described in :ref:`image-source-controls`. 385 * - ``V4L2_CTRL_CLASS_IMAGE_PROC`` 386 - 0x9f0000 387 - The class containing image processing controls. These controls are 388 described in :ref:`image-process-controls`. 389 * - ``V4L2_CTRL_CLASS_FM_RX`` 390 - 0xa10000 391 - The class containing FM Receiver (FM RX) controls. These controls 392 are described in :ref:`fm-rx-controls`. 393 * - ``V4L2_CTRL_CLASS_RF_TUNER`` 394 - 0xa20000 395 - The class containing RF tuner controls. These controls are 396 described in :ref:`rf-tuner-controls`. 397 * - ``V4L2_CTRL_CLASS_DETECT`` 398 - 0xa30000 399 - The class containing motion or object detection controls. These controls 400 are described in :ref:`detect-controls`. 401 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS`` 402 - 0xa40000 403 - The class containing stateless codec controls. These controls are 404 described in :ref:`codec-stateless-controls`. 405 406Return Value 407============ 408 409On success 0 is returned, on error -1 and the ``errno`` variable is set 410appropriately. The generic error codes are described at the 411:ref:`Generic Error Codes <gen-errors>` chapter. 412 413EINVAL 414 The struct :c:type:`v4l2_ext_control` ``id`` is 415 invalid, or the struct :c:type:`v4l2_ext_controls` 416 ``which`` is invalid, or the struct 417 :c:type:`v4l2_ext_control` ``value`` was 418 inappropriate (e.g. the given menu index is not supported by the 419 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` 420 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL`` 421 is not supported by the kernel. 422 This error code is also returned by the 423 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or 424 more control values are in conflict. 425 426ERANGE 427 The struct :c:type:`v4l2_ext_control` ``value`` 428 is out of bounds. 429 430EBUSY 431 The control is temporarily not changeable, possibly because another 432 applications took over control of the device function this control 433 belongs to, or (if the ``which`` field was set to 434 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet 435 completed. 436 437ENOSPC 438 The space reserved for the control's payload is insufficient. The 439 field ``size`` is set to a value that is enough to store the payload 440 and this error code is returned. 441 442EACCES 443 Attempt to try or set a read-only control, or to get a write-only 444 control, or to get a control from a request that has not yet been 445 completed. 446 447 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the 448 device does not support requests. 449