diff options
Diffstat (limited to 'Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst')
| -rw-r--r-- | Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst | 492 |
1 files changed, 492 insertions, 0 deletions
diff --git a/Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst b/Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst new file mode 100644 index 000000000000..39e24ad4b825 --- /dev/null +++ b/Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst @@ -0,0 +1,492 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _VIDIOC_G_EXT_CTRLS: + +****************************************************************** +ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS +****************************************************************** + +Name +==== + +VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values + + +Synopsis +======== + +.. cpp:function:: int ioctl( int fd, int request, struct v4l2_ext_controls *argp ) + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``request`` + VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, + VIDIOC_TRY_EXT_CTRLS + +``argp`` + + +Description +=========== + +These ioctls allow the caller to get or set multiple controls +atomically. Control IDs are grouped into control classes (see +:ref:`ctrl-class`) and all controls in the control array must belong +to the same control class. + +Applications must always fill in the ``count``, ``which``, ``controls`` +and ``reserved`` fields of struct +:ref:`v4l2_ext_controls <v4l2-ext-controls>`, and initialize the +struct :ref:`v4l2_ext_control <v4l2-ext-control>` array pointed to +by the ``controls`` fields. + +To get the current value of a set of controls applications initialize +the ``id``, ``size`` and ``reserved2`` fields of each struct +:ref:`v4l2_ext_control <v4l2-ext-control>` and call the +:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls controls must also set the +``string`` field. Controls of compound types +(``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field. + +If the ``size`` is too small to receive the control result (only +relevant for pointer-type controls like strings), then the driver will +set ``size`` to a valid value and return an ``ENOSPC`` error code. You +should re-allocate the memory to this new size and try again. For the +string type it is possible that the same issue occurs again if the +string has grown in the meantime. It is recommended to call +:ref:`VIDIOC_QUERYCTRL` first and use +``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is +sufficient memory. + +N-dimensional arrays are set and retrieved row-by-row. You cannot set a +partial array, all elements have to be set or retrieved. The total size +is calculated as ``elems`` * ``elem_size``. These values can be obtained +by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`. + +To change the value of a set of controls applications initialize the +``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields +of each struct :ref:`v4l2_ext_control <v4l2-ext-control>` and call +the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all* +control values are valid. + +To check if a set of controls have correct values applications +initialize the ``id``, ``size``, ``reserved2`` and +``value/value64/string/ptr`` fields of each struct +:ref:`v4l2_ext_control <v4l2-ext-control>` and call the +:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong +values are automatically adjusted to a valid value or if an error is +returned. + +When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error +code. When the value is out of bounds drivers can choose to take the +closest valid value or return an ``ERANGE`` error code, whatever seems more +appropriate. In the first case the new value is set in struct +:ref:`v4l2_ext_control <v4l2-ext-control>`. If the new control value +is inappropriate (e.g. the given menu index is not supported by the menu +control), then this will also result in an ``EINVAL`` error code error. + +The driver will only set/get these controls if all control values are +correct. This prevents the situation where only some of the controls +were set/get. Only low-level errors (e. g. a failed i2c command) can +still cause this situation. + + +.. _v4l2-ext-control: + +.. flat-table:: struct v4l2_ext_control + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 1 2 + + + - .. row 1 + + - __u32 + + - ``id`` + + - + - Identifies the control, set by the application. + + - .. row 2 + + - __u32 + + - ``size`` + + - + - The total size in bytes of the payload of this control. This is + normally 0, but for pointer controls this should be set to the + size of the memory containing the payload, or that will receive + the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is + less than is required to store the payload result, then it is set + to a value large enough to store the payload result and ``ENOSPC`` is + returned. + + .. note:: For string controls, this ``size`` field should + not be confused with the length of the string. This field refers + to the size of the memory that contains the string. The actual + *length* of the string may well be much smaller. + + - .. row 3 + + - __u32 + + - ``reserved2``\ [1] + + - + - Reserved for future extensions. Drivers and applications must set + the array to zero. + + - .. row 4 + + - union + + - (anonymous) + + - .. row 5 + + - + - __s32 + + - ``value`` + + - New value or current value. Valid if this control is not of type + ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is + not set. + + - .. row 6 + + - + - __s64 + + - ``value64`` + + - New value or current value. Valid if this control is of type + ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is + not set. + + - .. row 7 + + - + - char * + + - ``string`` + + - A pointer to a string. Valid if this control is of type + ``V4L2_CTRL_TYPE_STRING``. + + - .. row 8 + + - + - __u8 * + + - ``p_u8`` + + - A pointer to a matrix control of unsigned 8-bit values. Valid if + this control is of type ``V4L2_CTRL_TYPE_U8``. + + - .. row 9 + + - + - __u16 * + + - ``p_u16`` + + - A pointer to a matrix control of unsigned 16-bit values. Valid if + this control is of type ``V4L2_CTRL_TYPE_U16``. + + - .. row 10 + + - + - __u32 * + + - ``p_u32`` + + - A pointer to a matrix control of unsigned 32-bit values. Valid if + this control is of type ``V4L2_CTRL_TYPE_U32``. + + - .. row 11 + + - + - void * + + - ``ptr`` + + - A pointer to a compound type which can be an N-dimensional array + and/or a compound type (the control's type is >= + ``V4L2_CTRL_COMPOUND_TYPES``). Valid if + ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control. + + + +.. _v4l2-ext-controls: + +.. flat-table:: struct v4l2_ext_controls + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 1 + + + - .. row 1 + + - union + + - (anonymous) + + - .. row 2 + + - + - __u32 + + - ``ctrl_class`` + + - The control class to which all controls belong, see + :ref:`ctrl-class`. Drivers that use a kernel framework for + handling controls will also accept a value of 0 here, meaning that + the controls can belong to any control class. Whether drivers + support this can be tested by setting ``ctrl_class`` to 0 and + calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that + succeeds, then the driver supports this feature. + + - .. row 3 + + - + - __u32 + + - ``which`` + + - Which value of the control to get/set/try. + ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the + control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default + value of the control. + + .. note:: You can only get the default value of the control, + you cannot set or try it. + + For backwards compatibility you can also use a control class here + (see :ref:`ctrl-class`). In that case all controls have to + belong to that control class. This usage is deprecated, instead + just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old + drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and + that require a control class here. You can test for such drivers + by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling + VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the + driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``. + + - .. row 4 + + - __u32 + + - ``count`` + + - The number of controls in the controls array. May also be zero. + + - .. row 5 + + - __u32 + + - ``error_idx`` + + - Set by the driver in case of an error. If the error is associated + with a particular control, then ``error_idx`` is set to the index + of that control. If the error is not related to a specific + control, or the validation step failed (see below), then + ``error_idx`` is set to ``count``. The value is undefined if the + ioctl returned 0 (success). + + Before controls are read from/written to hardware a validation + step takes place: this checks if all controls in the list are + valid controls, if no attempt is made to write to a read-only + control or read from a write-only control, and any other up-front + checks that can be done without accessing the hardware. The exact + validations done during this step are driver dependent since some + checks might require hardware access for some devices, thus making + it impossible to do those checks up-front. However, drivers should + make a best-effort to do as many up-front checks as possible. + + This check is done to avoid leaving the hardware in an + inconsistent state due to easy-to-avoid problems. But it leads to + another problem: the application needs to know whether an error + came from the validation step (meaning that the hardware was not + touched) or from an error during the actual reading from/writing + to hardware. + + The, in hindsight quite poor, solution for that is to set + ``error_idx`` to ``count`` if the validation failed. This has the + unfortunate side-effect that it is not possible to see which + control failed the validation. If the validation was successful + and the error happened while accessing the hardware, then + ``error_idx`` is less than ``count`` and only the controls up to + ``error_idx-1`` were read or written correctly, and the state of + the remaining controls is undefined. + + Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is + also no need to handle the validation step in this special way, so + ``error_idx`` will just be set to the control that failed the + validation step instead of to ``count``. This means that if + :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``, + then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the + actual control that failed the validation step. Unfortunately, + there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. + + - .. row 6 + + - __u32 + + - ``reserved``\ [2] + + - Reserved for future extensions. Drivers and applications must set + the array to zero. + + - .. row 7 + + - struct :ref:`v4l2_ext_control <v4l2-ext-control>` * + + - ``controls`` + + - Pointer to an array of ``count`` v4l2_ext_control structures. + Ignored if ``count`` equals zero. + + + +.. _ctrl-class: + +.. flat-table:: Control classes + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + + - .. row 1 + + - ``V4L2_CTRL_CLASS_USER`` + + - 0x980000 + + - The class containing user controls. These controls are described + in :ref:`control`. All controls that can be set using the + :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and + :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this + class. + + - .. row 2 + + - ``V4L2_CTRL_CLASS_MPEG`` + + - 0x990000 + + - The class containing MPEG compression controls. These controls are + described in :ref:`mpeg-controls`. + + - .. row 3 + + - ``V4L2_CTRL_CLASS_CAMERA`` + + - 0x9a0000 + + - The class containing camera controls. These controls are described + in :ref:`camera-controls`. + + - .. row 4 + + - ``V4L2_CTRL_CLASS_FM_TX`` + + - 0x9b0000 + + - The class containing FM Transmitter (FM TX) controls. These + controls are described in :ref:`fm-tx-controls`. + + - .. row 5 + + - ``V4L2_CTRL_CLASS_FLASH`` + + - 0x9c0000 + + - The class containing flash device controls. These controls are + described in :ref:`flash-controls`. + + - .. row 6 + + - ``V4L2_CTRL_CLASS_JPEG`` + + - 0x9d0000 + + - The class containing JPEG compression controls. These controls are + described in :ref:`jpeg-controls`. + + - .. row 7 + + - ``V4L2_CTRL_CLASS_IMAGE_SOURCE`` + + - 0x9e0000 + + - The class containing image source controls. These controls are + described in :ref:`image-source-controls`. + + - .. row 8 + + - ``V4L2_CTRL_CLASS_IMAGE_PROC`` + + - 0x9f0000 + + - The class containing image processing controls. These controls are + described in :ref:`image-process-controls`. + + - .. row 9 + + - ``V4L2_CTRL_CLASS_FM_RX`` + + - 0xa10000 + + - The class containing FM Receiver (FM RX) controls. These controls + are described in :ref:`fm-rx-controls`. + + - .. row 10 + + - ``V4L2_CTRL_CLASS_RF_TUNER`` + + - 0xa20000 + + - The class containing RF tuner controls. These controls are + described in :ref:`rf-tuner-controls`. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EINVAL + The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``id`` is + invalid, the struct :ref:`v4l2_ext_controls <v4l2-ext-controls>` + ``which`` is invalid, or the struct + :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was + inappropriate (e.g. the given menu index is not supported by the + driver). This error code is also returned by the + :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or + more control values are in conflict. + +ERANGE + The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` + is out of bounds. + +EBUSY + The control is temporarily not changeable, possibly because another + applications took over control of the device function this control + belongs to. + +ENOSPC + The space reserved for the control's payload is insufficient. The + field ``size`` is set to a value that is enough to store the payload + and this error code is returned. + +EACCES + Attempt to try or set a read-only control or to get a write-only + control. |