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