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{1.2cm}|p{3.0cm}|p{1.5cm}|p{11.8cm}| 122 123.. c:type:: v4l2_ext_control 124 125.. cssclass: longtable 126 127.. flat-table:: struct v4l2_ext_control 128 :header-rows: 0 129 :stub-columns: 0 130 :widths: 1 1 2 131 132 * - __u32 133 - ``id`` 134 - Identifies the control, set by the application. 135 * - __u32 136 - ``size`` 137 - The total size in bytes of the payload of this control. This is 138 normally 0, but for pointer controls this should be set to the 139 size of the memory containing the payload, or that will receive 140 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is 141 less than is required to store the payload result, then it is set 142 to a value large enough to store the payload result and ``ENOSPC`` is 143 returned. 144 145 .. note:: 146 147 For string controls, this ``size`` field should 148 not be confused with the length of the string. This field refers 149 to the size of the memory that contains the string. The actual 150 *length* of the string may well be much smaller. 151 * - __u32 152 - ``reserved2``\ [1] 153 - Reserved for future extensions. Drivers and applications must set 154 the array to zero. 155 * - union { 156 - (anonymous) 157 * - __s32 158 - ``value`` 159 - New value or current value. Valid if this control is not of type 160 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 161 not set. 162 * - __s64 163 - ``value64`` 164 - New value or current value. Valid if this control is of type 165 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 166 not set. 167 * - char * 168 - ``string`` 169 - A pointer to a string. Valid if this control is of type 170 ``V4L2_CTRL_TYPE_STRING``. 171 * - __u8 * 172 - ``p_u8`` 173 - A pointer to a matrix control of unsigned 8-bit values. Valid if 174 this control is of type ``V4L2_CTRL_TYPE_U8``. 175 * - __u16 * 176 - ``p_u16`` 177 - A pointer to a matrix control of unsigned 16-bit values. Valid if 178 this control is of type ``V4L2_CTRL_TYPE_U16``. 179 * - __u32 * 180 - ``p_u32`` 181 - A pointer to a matrix control of unsigned 32-bit values. Valid if 182 this control is of type ``V4L2_CTRL_TYPE_U32``. 183 * - struct :c:type:`v4l2_area` * 184 - ``p_area`` 185 - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is 186 of type ``V4L2_CTRL_TYPE_AREA``. 187 * - struct :c:type:`v4l2_ctrl_h264_sps` * 188 - ``p_h264_sps`` 189 - A pointer to a struct :c:type:`v4l2_ctrl_h264_sps`. Valid if this control is 190 of type ``V4L2_CTRL_TYPE_H264_SPS``. 191 * - struct :c:type:`v4l2_ctrl_h264_pps` * 192 - ``p_h264_pps`` 193 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pps`. Valid if this control is 194 of type ``V4L2_CTRL_TYPE_H264_PPS``. 195 * - struct :c:type:`v4l2_ctrl_h264_scaling_matrix` * 196 - ``p_h264_scaling_matrix`` 197 - A pointer to a struct :c:type:`v4l2_ctrl_h264_scaling_matrix`. Valid if this control is 198 of type ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX``. 199 * - struct :c:type:`v4l2_ctrl_h264_pred_weights` * 200 - ``p_h264_pred_weights`` 201 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pred_weights`. Valid if this control is 202 of type ``V4L2_CTRL_TYPE_H264_PRED_WEIGHTS``. 203 * - struct :c:type:`v4l2_ctrl_h264_slice_params` * 204 - ``p_h264_slice_params`` 205 - A pointer to a struct :c:type:`v4l2_ctrl_h264_slice_params`. Valid if this control is 206 of type ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS``. 207 * - struct :c:type:`v4l2_ctrl_h264_decode_params` * 208 - ``p_h264_decode_params`` 209 - A pointer to a struct :c:type:`v4l2_ctrl_h264_decode_params`. Valid if this control is 210 of type ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS``. 211 * - struct :c:type:`v4l2_ctrl_fwht_params` * 212 - ``p_fwht_params`` 213 - A pointer to a struct :c:type:`v4l2_ctrl_fwht_params`. Valid if this control is 214 of type ``V4L2_CTRL_TYPE_FWHT_PARAMS``. 215 * - void * 216 - ``ptr`` 217 - A pointer to a compound type which can be an N-dimensional array 218 and/or a compound type (the control's type is >= 219 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if 220 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control. 221 * - } 222 - 223 224.. tabularcolumns:: |p{4.0cm}|p{2.2cm}|p{2.1cm}|p{8.2cm}| 225 226.. c:type:: v4l2_ext_controls 227 228.. cssclass:: longtable 229 230.. flat-table:: struct v4l2_ext_controls 231 :header-rows: 0 232 :stub-columns: 0 233 :widths: 1 1 2 234 235 * - union { 236 - (anonymous) 237 * - __u32 238 - ``ctrl_class`` 239 - The control class to which all controls belong, see 240 :ref:`ctrl-class`. Drivers that use a kernel framework for 241 handling controls will also accept a value of 0 here, meaning that 242 the controls can belong to any control class. Whether drivers 243 support this can be tested by setting ``ctrl_class`` to 0 and 244 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that 245 succeeds, then the driver supports this feature. 246 * - __u32 247 - ``which`` 248 - Which value of the control to get/set/try. 249 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the 250 control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default 251 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that 252 these controls have to be retrieved from a request or tried/set for 253 a request. In the latter case the ``request_fd`` field contains the 254 file descriptor of the request that should be used. If the device 255 does not support requests, then ``EACCES`` will be returned. 256 257 .. note:: 258 259 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only 260 get the default value of the control, you cannot set or try it. 261 262 For backwards compatibility you can also use a control class here 263 (see :ref:`ctrl-class`). In that case all controls have to 264 belong to that control class. This usage is deprecated, instead 265 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old 266 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and 267 that require a control class here. You can test for such drivers 268 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling 269 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the 270 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``. 271 * - } 272 - 273 * - __u32 274 - ``count`` 275 - The number of controls in the controls array. May also be zero. 276 * - __u32 277 - ``error_idx`` 278 - Set by the driver in case of an error. If the error is associated 279 with a particular control, then ``error_idx`` is set to the index 280 of that control. If the error is not related to a specific 281 control, or the validation step failed (see below), then 282 ``error_idx`` is set to ``count``. The value is undefined if the 283 ioctl returned 0 (success). 284 285 Before controls are read from/written to hardware a validation 286 step takes place: this checks if all controls in the list are 287 valid controls, if no attempt is made to write to a read-only 288 control or read from a write-only control, and any other up-front 289 checks that can be done without accessing the hardware. The exact 290 validations done during this step are driver dependent since some 291 checks might require hardware access for some devices, thus making 292 it impossible to do those checks up-front. However, drivers should 293 make a best-effort to do as many up-front checks as possible. 294 295 This check is done to avoid leaving the hardware in an 296 inconsistent state due to easy-to-avoid problems. But it leads to 297 another problem: the application needs to know whether an error 298 came from the validation step (meaning that the hardware was not 299 touched) or from an error during the actual reading from/writing 300 to hardware. 301 302 The, in hindsight quite poor, solution for that is to set 303 ``error_idx`` to ``count`` if the validation failed. This has the 304 unfortunate side-effect that it is not possible to see which 305 control failed the validation. If the validation was successful 306 and the error happened while accessing the hardware, then 307 ``error_idx`` is less than ``count`` and only the controls up to 308 ``error_idx-1`` were read or written correctly, and the state of 309 the remaining controls is undefined. 310 311 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is 312 also no need to handle the validation step in this special way, so 313 ``error_idx`` will just be set to the control that failed the 314 validation step instead of to ``count``. This means that if 315 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``, 316 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the 317 actual control that failed the validation step. Unfortunately, 318 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. 319 * - __s32 320 - ``request_fd`` 321 - File descriptor of the request to be used by this operation. Only 322 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``. 323 If the device does not support requests, then ``EACCES`` will be returned. 324 If requests are supported but an invalid request file descriptor is 325 given, then ``EINVAL`` will be returned. 326 * - __u32 327 - ``reserved``\ [1] 328 - Reserved for future extensions. 329 330 Drivers and applications must set the array to zero. 331 * - struct :c:type:`v4l2_ext_control` * 332 - ``controls`` 333 - Pointer to an array of ``count`` v4l2_ext_control structures. 334 335 Ignored if ``count`` equals zero. 336 337.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 338 339.. _ctrl-class: 340 341.. flat-table:: Control classes 342 :header-rows: 0 343 :stub-columns: 0 344 :widths: 3 1 4 345 346 * - ``V4L2_CTRL_CLASS_USER`` 347 - 0x980000 348 - The class containing user controls. These controls are described 349 in :ref:`control`. All controls that can be set using the 350 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and 351 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this 352 class. 353 * - ``V4L2_CTRL_CLASS_CODEC`` 354 - 0x990000 355 - The class containing stateful codec controls. These controls are 356 described in :ref:`codec-controls`. 357 * - ``V4L2_CTRL_CLASS_CAMERA`` 358 - 0x9a0000 359 - The class containing camera controls. These controls are described 360 in :ref:`camera-controls`. 361 * - ``V4L2_CTRL_CLASS_FM_TX`` 362 - 0x9b0000 363 - The class containing FM Transmitter (FM TX) controls. These 364 controls are described in :ref:`fm-tx-controls`. 365 * - ``V4L2_CTRL_CLASS_FLASH`` 366 - 0x9c0000 367 - The class containing flash device controls. These controls are 368 described in :ref:`flash-controls`. 369 * - ``V4L2_CTRL_CLASS_JPEG`` 370 - 0x9d0000 371 - The class containing JPEG compression controls. These controls are 372 described in :ref:`jpeg-controls`. 373 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` 374 - 0x9e0000 375 - The class containing image source controls. These controls are 376 described in :ref:`image-source-controls`. 377 * - ``V4L2_CTRL_CLASS_IMAGE_PROC`` 378 - 0x9f0000 379 - The class containing image processing controls. These controls are 380 described in :ref:`image-process-controls`. 381 * - ``V4L2_CTRL_CLASS_FM_RX`` 382 - 0xa10000 383 - The class containing FM Receiver (FM RX) controls. These controls 384 are described in :ref:`fm-rx-controls`. 385 * - ``V4L2_CTRL_CLASS_RF_TUNER`` 386 - 0xa20000 387 - The class containing RF tuner controls. These controls are 388 described in :ref:`rf-tuner-controls`. 389 * - ``V4L2_CTRL_CLASS_DETECT`` 390 - 0xa30000 391 - The class containing motion or object detection controls. These controls 392 are described in :ref:`detect-controls`. 393 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS`` 394 - 0xa40000 395 - The class containing stateless codec controls. These controls are 396 described in :ref:`codec-stateless-controls`. 397 398Return Value 399============ 400 401On success 0 is returned, on error -1 and the ``errno`` variable is set 402appropriately. The generic error codes are described at the 403:ref:`Generic Error Codes <gen-errors>` chapter. 404 405EINVAL 406 The struct :c:type:`v4l2_ext_control` ``id`` is 407 invalid, or the struct :c:type:`v4l2_ext_controls` 408 ``which`` is invalid, or the struct 409 :c:type:`v4l2_ext_control` ``value`` was 410 inappropriate (e.g. the given menu index is not supported by the 411 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` 412 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL`` 413 is not supported by the kernel. 414 This error code is also returned by the 415 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or 416 more control values are in conflict. 417 418ERANGE 419 The struct :c:type:`v4l2_ext_control` ``value`` 420 is out of bounds. 421 422EBUSY 423 The control is temporarily not changeable, possibly because another 424 applications took over control of the device function this control 425 belongs to, or (if the ``which`` field was set to 426 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet 427 completed. 428 429ENOSPC 430 The space reserved for the control's payload is insufficient. The 431 field ``size`` is set to a value that is enough to store the payload 432 and this error code is returned. 433 434EACCES 435 Attempt to try or set a read-only control, or to get a write-only 436 control, or to get a control from a request that has not yet been 437 completed. 438 439 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the 440 device does not support requests. 441