diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/media/uapi/v4l/vidioc-g-fmt.rst | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/Documentation/media/uapi/v4l/vidioc-g-fmt.rst b/Documentation/media/uapi/v4l/vidioc-g-fmt.rst new file mode 100644 index 000000000..3ead350e0 --- /dev/null +++ b/Documentation/media/uapi/v4l/vidioc-g-fmt.rst @@ -0,0 +1,156 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _VIDIOC_G_FMT: + +************************************************ +ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT +************************************************ + +Name +==== + +VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_G_FMT, struct v4l2_format *argp ) + :name: VIDIOC_G_FMT + +.. c:function:: int ioctl( int fd, VIDIOC_S_FMT, struct v4l2_format *argp ) + :name: VIDIOC_S_FMT + +.. c:function:: int ioctl( int fd, VIDIOC_TRY_FMT, struct v4l2_format *argp ) + :name: VIDIOC_TRY_FMT + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to struct :c:type:`v4l2_format`. + + +Description +=========== + +These ioctls are used to negotiate the format of data (typically image +format) exchanged between driver and application. + +To query the current parameters applications set the ``type`` field of a +struct :c:type:`v4l2_format` to the respective buffer (stream) +type. For example video capture devices use +``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or +``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the +:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills +the respective member of the ``fmt`` union. In case of video capture +devices that is either the struct +:c:type:`v4l2_pix_format` ``pix`` or the struct +:c:type:`v4l2_pix_format_mplane` ``pix_mp`` +member. When the requested buffer type is not supported drivers return +an ``EINVAL`` error code. + +To change the current format parameters applications initialize the +``type`` field and all fields of the respective ``fmt`` union member. +For details see the documentation of the various devices types in +:ref:`devices`. Good practice is to query the current parameters +first, and to modify only those parameters not suitable for the +application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with +a pointer to a struct :c:type:`v4l2_format` structure the driver +checks and adjusts the parameters against hardware abilities. Drivers +should not return an error code unless the ``type`` field is invalid, +this is a mechanism to fathom device capabilities and to approach +parameters acceptable for both the application and driver. On success +the driver may program the hardware, allocate resources and generally +prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns +the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple, +inflexible devices may even ignore all input and always return the +default parameters. However all V4L2 devices exchanging data with the +application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` +ioctl. When the requested buffer type is not supported drivers return an +EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in +progress or the resource is not available for other reasons drivers +return the ``EBUSY`` error code. + +The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one +exception: it does not change driver state. It can also be called at any +time, never returning ``EBUSY``. This function is provided to negotiate +parameters, to learn about hardware limitations, without disabling I/O +or possibly time consuming hardware preparations. Although strongly +recommended drivers are not required to implement this ioctl. + +The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what +:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output. + + +.. c:type:: v4l2_format + +.. tabularcolumns:: |p{1.2cm}|p{4.6cm}|p{3.0cm}|p{8.6cm}| + +.. flat-table:: struct v4l2_format + :header-rows: 0 + :stub-columns: 0 + + * - __u32 + - ``type`` + - + - Type of the data stream, see :c:type:`v4l2_buf_type`. + * - union + - ``fmt`` + * - + - struct :c:type:`v4l2_pix_format` + - ``pix`` + - Definition of an image format, see :ref:`pixfmt`, used by video + capture and output devices. + * - + - struct :c:type:`v4l2_pix_format_mplane` + - ``pix_mp`` + - Definition of an image format, see :ref:`pixfmt`, used by video + capture and output devices that support the + :ref:`multi-planar version of the API <planar-apis>`. + * - + - struct :c:type:`v4l2_window` + - ``win`` + - Definition of an overlaid image, see :ref:`overlay`, used by + video overlay devices. + * - + - struct :c:type:`v4l2_vbi_format` + - ``vbi`` + - Raw VBI capture or output parameters. This is discussed in more + detail in :ref:`raw-vbi`. Used by raw VBI capture and output + devices. + * - + - struct :c:type:`v4l2_sliced_vbi_format` + - ``sliced`` + - Sliced VBI capture or output parameters. See :ref:`sliced` for + details. Used by sliced VBI capture and output devices. + * - + - struct :c:type:`v4l2_sdr_format` + - ``sdr`` + - Definition of a data format, see :ref:`pixfmt`, used by SDR + capture and output devices. + * - + - __u8 + - ``raw_data``\ [200] + - Place holder for future extensions. + + +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 :c:type:`v4l2_format` ``type`` field is + invalid or the requested buffer type not supported. + +EBUSY + The device is busy and cannot change the format. This could be + because or the device is streaming or buffers are allocated or + queued to the driver. Relevant for :ref:`VIDIOC_S_FMT + <VIDIOC_G_FMT>` only. |