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/media/uapi/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 1 2 140 141 * - __u32 142 - ``id`` 143 - 144 - Identifies the control, set by the application. 145 * - __u32 146 - ``size`` 147 - 148 - The total size in bytes of the payload of this control. This is 149 normally 0, but for pointer controls this should be set to the 150 size of the memory containing the payload, or that will receive 151 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is 152 less than is required to store the payload result, then it is set 153 to a value large enough to store the payload result and ``ENOSPC`` is 154 returned. 155 156 .. note:: 157 158 For string controls, this ``size`` field should 159 not be confused with the length of the string. This field refers 160 to the size of the memory that contains the string. The actual 161 *length* of the string may well be much smaller. 162 * - __u32 163 - ``reserved2``\ [1] 164 - 165 - Reserved for future extensions. Drivers and applications must set 166 the array to zero. 167 * - union 168 - (anonymous) 169 * - 170 - __s32 171 - ``value`` 172 - New value or current value. Valid if this control is not of type 173 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 174 not set. 175 * - 176 - __s64 177 - ``value64`` 178 - New value or current value. Valid if this control is of type 179 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is 180 not set. 181 * - 182 - char * 183 - ``string`` 184 - A pointer to a string. Valid if this control is of type 185 ``V4L2_CTRL_TYPE_STRING``. 186 * - 187 - __u8 * 188 - ``p_u8`` 189 - A pointer to a matrix control of unsigned 8-bit values. Valid if 190 this control is of type ``V4L2_CTRL_TYPE_U8``. 191 * - 192 - __u16 * 193 - ``p_u16`` 194 - A pointer to a matrix control of unsigned 16-bit values. Valid if 195 this control is of type ``V4L2_CTRL_TYPE_U16``. 196 * - 197 - __u32 * 198 - ``p_u32`` 199 - A pointer to a matrix control of unsigned 32-bit values. Valid if 200 this control is of type ``V4L2_CTRL_TYPE_U32``. 201 * - 202 - void * 203 - ``ptr`` 204 - A pointer to a compound type which can be an N-dimensional array 205 and/or a compound type (the control's type is >= 206 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if 207 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control. 208 209 210.. tabularcolumns:: |p{4.0cm}|p{2.2cm}|p{2.1cm}|p{8.2cm}| 211 212.. c:type:: v4l2_ext_controls 213 214.. cssclass:: longtable 215 216.. flat-table:: struct v4l2_ext_controls 217 :header-rows: 0 218 :stub-columns: 0 219 :widths: 1 1 2 1 220 221 * - union 222 - (anonymous) 223 * - 224 - __u32 225 - ``ctrl_class`` 226 - The control class to which all controls belong, see 227 :ref:`ctrl-class`. Drivers that use a kernel framework for 228 handling controls will also accept a value of 0 here, meaning that 229 the controls can belong to any control class. Whether drivers 230 support this can be tested by setting ``ctrl_class`` to 0 and 231 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that 232 succeeds, then the driver supports this feature. 233 * - 234 - __u32 235 - ``which`` 236 - Which value of the control to get/set/try. 237 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the 238 control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default 239 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that 240 these controls have to be retrieved from a request or tried/set for 241 a request. In the latter case the ``request_fd`` field contains the 242 file descriptor of the request that should be used. If the device 243 does not support requests, then ``EACCES`` will be returned. 244 245 .. note:: 246 247 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only 248 get the default value of the control, you cannot set or try it. 249 250 For backwards compatibility you can also use a control class here 251 (see :ref:`ctrl-class`). In that case all controls have to 252 belong to that control class. This usage is deprecated, instead 253 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old 254 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and 255 that require a control class here. You can test for such drivers 256 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling 257 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the 258 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``. 259 * - __u32 260 - ``count`` 261 - The number of controls in the controls array. May also be zero. 262 * - __u32 263 - ``error_idx`` 264 - Set by the driver in case of an error. If the error is associated 265 with a particular control, then ``error_idx`` is set to the index 266 of that control. If the error is not related to a specific 267 control, or the validation step failed (see below), then 268 ``error_idx`` is set to ``count``. The value is undefined if the 269 ioctl returned 0 (success). 270 271 Before controls are read from/written to hardware a validation 272 step takes place: this checks if all controls in the list are 273 valid controls, if no attempt is made to write to a read-only 274 control or read from a write-only control, and any other up-front 275 checks that can be done without accessing the hardware. The exact 276 validations done during this step are driver dependent since some 277 checks might require hardware access for some devices, thus making 278 it impossible to do those checks up-front. However, drivers should 279 make a best-effort to do as many up-front checks as possible. 280 281 This check is done to avoid leaving the hardware in an 282 inconsistent state due to easy-to-avoid problems. But it leads to 283 another problem: the application needs to know whether an error 284 came from the validation step (meaning that the hardware was not 285 touched) or from an error during the actual reading from/writing 286 to hardware. 287 288 The, in hindsight quite poor, solution for that is to set 289 ``error_idx`` to ``count`` if the validation failed. This has the 290 unfortunate side-effect that it is not possible to see which 291 control failed the validation. If the validation was successful 292 and the error happened while accessing the hardware, then 293 ``error_idx`` is less than ``count`` and only the controls up to 294 ``error_idx-1`` were read or written correctly, and the state of 295 the remaining controls is undefined. 296 297 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is 298 also no need to handle the validation step in this special way, so 299 ``error_idx`` will just be set to the control that failed the 300 validation step instead of to ``count``. This means that if 301 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``, 302 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the 303 actual control that failed the validation step. Unfortunately, 304 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. 305 * - __s32 306 - ``request_fd`` 307 - File descriptor of the request to be used by this operation. Only 308 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``. 309 If the device does not support requests, then ``EACCES`` will be returned. 310 If requests are supported but an invalid request file descriptor is 311 given, then ``EINVAL`` will be returned. 312 * - __u32 313 - ``reserved``\ [1] 314 - Reserved for future extensions. 315 316 Drivers and applications must set the array to zero. 317 * - struct :c:type:`v4l2_ext_control` * 318 - ``controls`` 319 - Pointer to an array of ``count`` v4l2_ext_control structures. 320 321 Ignored if ``count`` equals zero. 322 323 324.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 325 326.. _ctrl-class: 327 328.. flat-table:: Control classes 329 :header-rows: 0 330 :stub-columns: 0 331 :widths: 3 1 4 332 333 * - ``V4L2_CTRL_CLASS_USER`` 334 - 0x980000 335 - The class containing user controls. These controls are described 336 in :ref:`control`. All controls that can be set using the 337 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and 338 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this 339 class. 340 * - ``V4L2_CTRL_CLASS_MPEG`` 341 - 0x990000 342 - The class containing MPEG compression controls. These controls are 343 described in :ref:`mpeg-controls`. 344 * - ``V4L2_CTRL_CLASS_CAMERA`` 345 - 0x9a0000 346 - The class containing camera controls. These controls are described 347 in :ref:`camera-controls`. 348 * - ``V4L2_CTRL_CLASS_FM_TX`` 349 - 0x9b0000 350 - The class containing FM Transmitter (FM TX) controls. These 351 controls are described in :ref:`fm-tx-controls`. 352 * - ``V4L2_CTRL_CLASS_FLASH`` 353 - 0x9c0000 354 - The class containing flash device controls. These controls are 355 described in :ref:`flash-controls`. 356 * - ``V4L2_CTRL_CLASS_JPEG`` 357 - 0x9d0000 358 - The class containing JPEG compression controls. These controls are 359 described in :ref:`jpeg-controls`. 360 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` 361 - 0x9e0000 362 - The class containing image source controls. These controls are 363 described in :ref:`image-source-controls`. 364 * - ``V4L2_CTRL_CLASS_IMAGE_PROC`` 365 - 0x9f0000 366 - The class containing image processing controls. These controls are 367 described in :ref:`image-process-controls`. 368 * - ``V4L2_CTRL_CLASS_FM_RX`` 369 - 0xa10000 370 - The class containing FM Receiver (FM RX) controls. These controls 371 are described in :ref:`fm-rx-controls`. 372 * - ``V4L2_CTRL_CLASS_RF_TUNER`` 373 - 0xa20000 374 - The class containing RF tuner controls. These controls are 375 described in :ref:`rf-tuner-controls`. 376 377 378Return Value 379============ 380 381On success 0 is returned, on error -1 and the ``errno`` variable is set 382appropriately. The generic error codes are described at the 383:ref:`Generic Error Codes <gen-errors>` chapter. 384 385EINVAL 386 The struct :c:type:`v4l2_ext_control` ``id`` is 387 invalid, or the struct :c:type:`v4l2_ext_controls` 388 ``which`` is invalid, or the struct 389 :c:type:`v4l2_ext_control` ``value`` was 390 inappropriate (e.g. the given menu index is not supported by the 391 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` 392 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL`` 393 is not supported by the kernel. 394 This error code is also returned by the 395 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or 396 more control values are in conflict. 397 398ERANGE 399 The struct :c:type:`v4l2_ext_control` ``value`` 400 is out of bounds. 401 402EBUSY 403 The control is temporarily not changeable, possibly because another 404 applications took over control of the device function this control 405 belongs to, or (if the ``which`` field was set to 406 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet 407 completed. 408 409ENOSPC 410 The space reserved for the control's payload is insufficient. The 411 field ``size`` is set to a value that is enough to store the payload 412 and this error code is returned. 413 414EACCES 415 Attempt to try or set a read-only control, or to get a write-only 416 control, or to get a control from a request that has not yet been 417 completed. 418 419 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the 420 device does not support requests. 421