1.. Permission is granted to copy, distribute and/or modify this 2.. document under the terms of the GNU Free Documentation License, 3.. Version 1.1 or any later version published by the Free Software 4.. Foundation, with no Invariant Sections, no Front-Cover Texts 5.. and no Back-Cover Texts. A copy of the license is included at 6.. Documentation/userspace-api/media/fdl-appendix.rst. 7.. 8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections 9 10.. _VIDIOC_G_EXT_CTRLS: 11 12****************************************************************** 13ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS 14****************************************************************** 15 16Name 17==== 18 19VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values 20 21 22Synopsis 23======== 24 25.. c:function:: int ioctl( int fd, VIDIOC_G_EXT_CTRLS, struct v4l2_ext_controls *argp ) 26 :name: VIDIOC_G_EXT_CTRLS 27 28 29.. c:function:: int ioctl( int fd, VIDIOC_S_EXT_CTRLS, struct v4l2_ext_controls *argp ) 30 :name: VIDIOC_S_EXT_CTRLS 31 32 33.. c:function:: int ioctl( int fd, VIDIOC_TRY_EXT_CTRLS, struct v4l2_ext_controls *argp ) 34 :name: VIDIOC_TRY_EXT_CTRLS 35 36 37Arguments 38========= 39 40``fd`` 41 File descriptor returned by :ref:`open() <func-open>`. 42 43``argp`` 44 Pointer to struct :c:type:`v4l2_ext_controls`. 45 46 47Description 48=========== 49 50These ioctls allow the caller to get or set multiple controls 51atomically. Control IDs are grouped into control classes (see 52:ref:`ctrl-class`) and all controls in the control array must belong 53to the same control class. 54 55Applications must always fill in the ``count``, ``which``, ``controls`` 56and ``reserved`` fields of struct 57:c:type:`v4l2_ext_controls`, and initialize the 58struct :c:type:`v4l2_ext_control` array pointed to 59by the ``controls`` fields. 60 61To get the current value of a set of controls applications initialize 62the ``id``, ``size`` and ``reserved2`` fields of each struct 63:c:type:`v4l2_ext_control` and call the 64:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls controls must also set the 65``string`` field. Controls of compound types 66(``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field. 67 68If the ``size`` is too small to receive the control result (only 69relevant for pointer-type controls like strings), then the driver will 70set ``size`` to a valid value and return an ``ENOSPC`` error code. You 71should re-allocate the memory to this new size and try again. For the 72string type it is possible that the same issue occurs again if the 73string has grown in the meantime. It is recommended to call 74:ref:`VIDIOC_QUERYCTRL` first and use 75``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is 76sufficient memory. 77 78N-dimensional arrays are set and retrieved row-by-row. You cannot set a 79partial array, all elements have to be set or retrieved. The total size 80is calculated as ``elems`` * ``elem_size``. These values can be obtained 81by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`. 82 83To change the value of a set of controls applications initialize the 84``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields 85of each struct :c:type:`v4l2_ext_control` and call 86the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all* 87control values are valid. 88 89To check if a set of controls have correct values applications 90initialize the ``id``, ``size``, ``reserved2`` and 91``value/value64/string/ptr`` fields of each struct 92:c:type:`v4l2_ext_control` and call the 93:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong 94values are automatically adjusted to a valid value or if an error is 95returned. 96 97When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error 98code. When the value is out of bounds drivers can choose to take the 99closest valid value or return an ``ERANGE`` error code, whatever seems more 100appropriate. In the first case the new value is set in struct 101:c:type:`v4l2_ext_control`. If the new control value 102is inappropriate (e.g. the given menu index is not supported by the menu 103control), then this will also result in an ``EINVAL`` error code error. 104 105If ``request_fd`` is set to a not-yet-queued :ref:`request <media-request-api>` 106file descriptor and ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``, 107then the controls are not applied immediately when calling 108:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, but instead are applied by 109the driver for the buffer associated with the same request. 110If the device does not support requests, then ``EACCES`` will be returned. 111If requests are supported but an invalid request file descriptor is given, 112then ``EINVAL`` will be returned. 113 114An attempt to call :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` for a 115request that has already been queued will result in an ``EBUSY`` error. 116 117If ``request_fd`` is specified and ``which`` is set to 118``V4L2_CTRL_WHICH_REQUEST_VAL`` during a call to 119:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then it will return the 120values of the controls at the time of request completion. 121If the request is not yet completed, then this will result in an 122``EACCES`` error. 123 124The driver will only set/get these controls if all control values are 125correct. This prevents the situation where only some of the controls 126were set/get. Only low-level errors (e. g. a failed i2c command) can 127still cause this situation. 128 129 130.. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{1.5cm}|p{11.8cm}| 131 132.. c:type:: v4l2_ext_control 133 134.. cssclass: longtable 135 136.. flat-table:: struct v4l2_ext_control 137 :header-rows: 0 138 :stub-columns: 0 139 :widths: 1 1 2 140 141 * - __u32 142 - ``id`` 143 - Identifies the control, set by the application. 144 * - __u32 145 - ``size`` 146 - The total size in bytes of the payload of this control. This is 147 normally 0, but for pointer controls this should be set to the 148 size of the memory containing the payload, or that will receive 149 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is 150 less than is required to store the payload result, then it is set 151 to a value large enough to store the payload result and ``ENOSPC`` is 152 returned. 153 154 .. note:: 155 156 For string controls, this ``size`` field should 157 not be confused with the length of the string. This field refers 158 to the size of the memory that contains the string. The actual 159 *length* of the string may well be much smaller. 160 * - __u32 161 - ``reserved2``\ [1] 162 - Reserved for future extensions. Drivers and applications must set 163 the array to zero. 164 * - union { 165 - (anonymous) 166 * - __s32 167 - ``value`` 168 - New value or current value. Valid if this control is not of type 169 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 170 not set. 171 * - __s64 172 - ``value64`` 173 - New value or current value. Valid if this control is of type 174 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 175 not set. 176 * - char * 177 - ``string`` 178 - A pointer to a string. Valid if this control is of type 179 ``V4L2_CTRL_TYPE_STRING``. 180 * - __u8 * 181 - ``p_u8`` 182 - A pointer to a matrix control of unsigned 8-bit values. Valid if 183 this control is of type ``V4L2_CTRL_TYPE_U8``. 184 * - __u16 * 185 - ``p_u16`` 186 - A pointer to a matrix control of unsigned 16-bit values. Valid if 187 this control is of type ``V4L2_CTRL_TYPE_U16``. 188 * - __u32 * 189 - ``p_u32`` 190 - A pointer to a matrix control of unsigned 32-bit values. Valid if 191 this control is of type ``V4L2_CTRL_TYPE_U32``. 192 * - :c:type:`v4l2_area` * 193 - ``p_area`` 194 - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is 195 of type ``V4L2_CTRL_TYPE_AREA``. 196 * - void * 197 - ``ptr`` 198 - A pointer to a compound type which can be an N-dimensional array 199 and/or a compound type (the control's type is >= 200 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if 201 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control. 202 * - } 203 - 204 205 206.. tabularcolumns:: |p{4.0cm}|p{2.2cm}|p{2.1cm}|p{8.2cm}| 207 208.. c:type:: v4l2_ext_controls 209 210.. cssclass:: longtable 211 212.. flat-table:: struct v4l2_ext_controls 213 :header-rows: 0 214 :stub-columns: 0 215 :widths: 1 1 2 216 217 * - union { 218 - (anonymous) 219 * - __u32 220 - ``ctrl_class`` 221 - The control class to which all controls belong, see 222 :ref:`ctrl-class`. Drivers that use a kernel framework for 223 handling controls will also accept a value of 0 here, meaning that 224 the controls can belong to any control class. Whether drivers 225 support this can be tested by setting ``ctrl_class`` to 0 and 226 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that 227 succeeds, then the driver supports this feature. 228 * - __u32 229 - ``which`` 230 - Which value of the control to get/set/try. 231 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the 232 control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default 233 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that 234 these controls have to be retrieved from a request or tried/set for 235 a request. In the latter case the ``request_fd`` field contains the 236 file descriptor of the request that should be used. If the device 237 does not support requests, then ``EACCES`` will be returned. 238 239 .. note:: 240 241 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only 242 get the default value of the control, you cannot set or try it. 243 244 For backwards compatibility you can also use a control class here 245 (see :ref:`ctrl-class`). In that case all controls have to 246 belong to that control class. This usage is deprecated, instead 247 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old 248 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and 249 that require a control class here. You can test for such drivers 250 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling 251 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the 252 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``. 253 * - } 254 - 255 * - __u32 256 - ``count`` 257 - The number of controls in the controls array. May also be zero. 258 * - __u32 259 - ``error_idx`` 260 - Set by the driver in case of an error. If the error is associated 261 with a particular control, then ``error_idx`` is set to the index 262 of that control. If the error is not related to a specific 263 control, or the validation step failed (see below), then 264 ``error_idx`` is set to ``count``. The value is undefined if the 265 ioctl returned 0 (success). 266 267 Before controls are read from/written to hardware a validation 268 step takes place: this checks if all controls in the list are 269 valid controls, if no attempt is made to write to a read-only 270 control or read from a write-only control, and any other up-front 271 checks that can be done without accessing the hardware. The exact 272 validations done during this step are driver dependent since some 273 checks might require hardware access for some devices, thus making 274 it impossible to do those checks up-front. However, drivers should 275 make a best-effort to do as many up-front checks as possible. 276 277 This check is done to avoid leaving the hardware in an 278 inconsistent state due to easy-to-avoid problems. But it leads to 279 another problem: the application needs to know whether an error 280 came from the validation step (meaning that the hardware was not 281 touched) or from an error during the actual reading from/writing 282 to hardware. 283 284 The, in hindsight quite poor, solution for that is to set 285 ``error_idx`` to ``count`` if the validation failed. This has the 286 unfortunate side-effect that it is not possible to see which 287 control failed the validation. If the validation was successful 288 and the error happened while accessing the hardware, then 289 ``error_idx`` is less than ``count`` and only the controls up to 290 ``error_idx-1`` were read or written correctly, and the state of 291 the remaining controls is undefined. 292 293 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is 294 also no need to handle the validation step in this special way, so 295 ``error_idx`` will just be set to the control that failed the 296 validation step instead of to ``count``. This means that if 297 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``, 298 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the 299 actual control that failed the validation step. Unfortunately, 300 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. 301 * - __s32 302 - ``request_fd`` 303 - File descriptor of the request to be used by this operation. Only 304 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``. 305 If the device does not support requests, then ``EACCES`` will be returned. 306 If requests are supported but an invalid request file descriptor is 307 given, then ``EINVAL`` will be returned. 308 * - __u32 309 - ``reserved``\ [1] 310 - Reserved for future extensions. 311 312 Drivers and applications must set the array to zero. 313 * - struct :c:type:`v4l2_ext_control` * 314 - ``controls`` 315 - Pointer to an array of ``count`` v4l2_ext_control structures. 316 317 Ignored if ``count`` equals zero. 318 319 320.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 321 322.. _ctrl-class: 323 324.. flat-table:: Control classes 325 :header-rows: 0 326 :stub-columns: 0 327 :widths: 3 1 4 328 329 * - ``V4L2_CTRL_CLASS_USER`` 330 - 0x980000 331 - The class containing user controls. These controls are described 332 in :ref:`control`. All controls that can be set using the 333 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and 334 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this 335 class. 336 * - ``V4L2_CTRL_CLASS_MPEG`` 337 - 0x990000 338 - The class containing MPEG compression controls. These controls are 339 described in :ref:`mpeg-controls`. 340 * - ``V4L2_CTRL_CLASS_CAMERA`` 341 - 0x9a0000 342 - The class containing camera controls. These controls are described 343 in :ref:`camera-controls`. 344 * - ``V4L2_CTRL_CLASS_FM_TX`` 345 - 0x9b0000 346 - The class containing FM Transmitter (FM TX) controls. These 347 controls are described in :ref:`fm-tx-controls`. 348 * - ``V4L2_CTRL_CLASS_FLASH`` 349 - 0x9c0000 350 - The class containing flash device controls. These controls are 351 described in :ref:`flash-controls`. 352 * - ``V4L2_CTRL_CLASS_JPEG`` 353 - 0x9d0000 354 - The class containing JPEG compression controls. These controls are 355 described in :ref:`jpeg-controls`. 356 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` 357 - 0x9e0000 358 - The class containing image source controls. These controls are 359 described in :ref:`image-source-controls`. 360 * - ``V4L2_CTRL_CLASS_IMAGE_PROC`` 361 - 0x9f0000 362 - The class containing image processing controls. These controls are 363 described in :ref:`image-process-controls`. 364 * - ``V4L2_CTRL_CLASS_FM_RX`` 365 - 0xa10000 366 - The class containing FM Receiver (FM RX) controls. These controls 367 are described in :ref:`fm-rx-controls`. 368 * - ``V4L2_CTRL_CLASS_RF_TUNER`` 369 - 0xa20000 370 - The class containing RF tuner controls. These controls are 371 described in :ref:`rf-tuner-controls`. 372 373 374Return Value 375============ 376 377On success 0 is returned, on error -1 and the ``errno`` variable is set 378appropriately. The generic error codes are described at the 379:ref:`Generic Error Codes <gen-errors>` chapter. 380 381EINVAL 382 The struct :c:type:`v4l2_ext_control` ``id`` is 383 invalid, or the struct :c:type:`v4l2_ext_controls` 384 ``which`` is invalid, or the struct 385 :c:type:`v4l2_ext_control` ``value`` was 386 inappropriate (e.g. the given menu index is not supported by the 387 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` 388 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL`` 389 is not supported by the kernel. 390 This error code is also returned by the 391 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or 392 more control values are in conflict. 393 394ERANGE 395 The struct :c:type:`v4l2_ext_control` ``value`` 396 is out of bounds. 397 398EBUSY 399 The control is temporarily not changeable, possibly because another 400 applications took over control of the device function this control 401 belongs to, or (if the ``which`` field was set to 402 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet 403 completed. 404 405ENOSPC 406 The space reserved for the control's payload is insufficient. The 407 field ``size`` is set to a value that is enough to store the payload 408 and this error code is returned. 409 410EACCES 411 Attempt to try or set a read-only control, or to get a write-only 412 control, or to get a control from a request that has not yet been 413 completed. 414 415 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the 416 device does not support requests. 417