vidioc-g-ext-ctrls.rst (20356B)
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.