media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 270 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst b/Documentation/userspace-api/media/v4l/vidioc-g-parm.rst
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+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _VIDIOC_G_PARM:
+
+**********************************
+ioctl VIDIOC_G_PARM, VIDIOC_S_PARM
+**********************************
+
+Name
+====
+
+VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_G_PARM, v4l2_streamparm *argp )
+    :name: VIDIOC_G_PARM
+
+.. c:function:: int ioctl( int fd, VIDIOC_S_PARM, v4l2_streamparm *argp )
+    :name: VIDIOC_S_PARM
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_streamparm`.
+
+
+Description
+===========
+
+The current video standard determines a nominal number of frames per
+second. If less than this number of frames is to be captured or output,
+applications can request frame skipping or duplicating on the driver
+side. This is especially useful when using the :ref:`read() <func-read>` or
+:ref:`write() <func-write>`, which are not augmented by timestamps or sequence
+counters, and to avoid unnecessary data copying.
+
+Changing the frame interval shall never change the format. Changing the
+format, on the other hand, may change the frame interval.
+
+Further these ioctls can be used to determine the number of buffers used
+internally by a driver in read/write mode. For implications see the
+section discussing the :ref:`read() <func-read>` function.
+
+To get and set the streaming parameters applications call the
+:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a
+pointer to a struct :c:type:`v4l2_streamparm` which contains a
+union holding separate parameters for input and output devices.
+
+
+.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
+
+.. c:type:: v4l2_streamparm
+
+.. flat-table:: struct v4l2_streamparm
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``type``
+      - The buffer (stream) type, same as struct
+	:c:type:`v4l2_format` ``type``, set by the
+	application. See :c:type:`v4l2_buf_type`.
+    * - union {
+      - ``parm``
+    * - struct :c:type:`v4l2_captureparm`
+      - ``capture``
+      - Parameters for capture devices, used when ``type`` is
+	``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
+	``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``.
+    * - struct :c:type:`v4l2_outputparm`
+      - ``output``
+      - Parameters for output devices, used when ``type`` is
+	``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``.
+    * - __u8
+      - ``raw_data``\ [200]
+      - A place holder for future extensions.
+    * - }
+      -
+
+
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_captureparm
+
+.. flat-table:: struct v4l2_captureparm
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``capability``
+      - See :ref:`parm-caps`.
+    * - __u32
+      - ``capturemode``
+      - Set by drivers and applications, see :ref:`parm-flags`.
+    * - struct :c:type:`v4l2_fract`
+      - ``timeperframe``
+      - This is the desired period between successive frames captured by
+	the driver, in seconds. The field is intended to skip frames on
+	the driver side, saving I/O bandwidth.
+
+	Applications store here the desired frame period, drivers return
+	the actual frame period, which must be greater or equal to the
+	nominal frame period determined by the current video standard
+	(struct :c:type:`v4l2_standard` ``frameperiod``
+	field). Changing the video standard (also implicitly by switching
+	the video input) may reset this parameter to the nominal frame
+	period. To reset manually applications can just set this field to
+	zero.
+
+	Drivers support this function only when they set the
+	``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
+    * - __u32
+      - ``extendedmode``
+      - Custom (driver specific) streaming parameters. When unused,
+	applications and drivers must set this field to zero. Applications
+	using this field should check the driver name and version, see
+	:ref:`querycap`.
+    * - __u32
+      - ``readbuffers``
+      - Applications set this field to the desired number of buffers used
+	internally by the driver in :ref:`read() <func-read>` mode.
+	Drivers return the actual number of buffers. When an application
+	requests zero buffers, drivers should just return the current
+	setting rather than the minimum or an error code. For details see
+	:ref:`rw`.
+    * - __u32
+      - ``reserved``\ [4]
+      - Reserved for future extensions. Drivers and applications must set
+	the array to zero.
+
+
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_outputparm
+
+.. flat-table:: struct v4l2_outputparm
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``capability``
+      - See :ref:`parm-caps`.
+    * - __u32
+      - ``outputmode``
+      - Set by drivers and applications, see :ref:`parm-flags`.
+    * - struct :c:type:`v4l2_fract`
+      - ``timeperframe``
+      - This is the desired period between successive frames output by the
+	driver, in seconds.
+    * - :cspan:`2`
+
+	The field is intended to repeat frames on the driver side in
+	:ref:`write() <func-write>` mode (in streaming mode timestamps
+	can be used to throttle the output), saving I/O bandwidth.
+
+	Applications store here the desired frame period, drivers return
+	the actual frame period, which must be greater or equal to the
+	nominal frame period determined by the current video standard
+	(struct :c:type:`v4l2_standard` ``frameperiod``
+	field). Changing the video standard (also implicitly by switching
+	the video output) may reset this parameter to the nominal frame
+	period. To reset manually applications can just set this field to
+	zero.
+
+	Drivers support this function only when they set the
+	``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
+    * - __u32
+      - ``extendedmode``
+      - Custom (driver specific) streaming parameters. When unused,
+	applications and drivers must set this field to zero. Applications
+	using this field should check the driver name and version, see
+	:ref:`querycap`.
+    * - __u32
+      - ``writebuffers``
+      - Applications set this field to the desired number of buffers used
+	internally by the driver in :ref:`write() <func-write>` mode. Drivers
+	return the actual number of buffers. When an application requests
+	zero buffers, drivers should just return the current setting
+	rather than the minimum or an error code. For details see
+	:ref:`rw`.
+    * - __u32
+      - ``reserved``\ [4]
+      - Reserved for future extensions. Drivers and applications must set
+	the array to zero.
+
+
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
+
+.. _parm-caps:
+
+.. flat-table:: Streaming Parameters Capabilities
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+    * - ``V4L2_CAP_TIMEPERFRAME``
+      - 0x1000
+      - The frame skipping/repeating controlled by the ``timeperframe``
+	field is supported.
+
+
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
+
+.. _parm-flags:
+
+.. flat-table:: Capture Parameters Flags
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+    * - ``V4L2_MODE_HIGHQUALITY``
+      - 0x0001
+      - High quality imaging mode. High quality mode is intended for still
+	imaging applications. The idea is to get the best possible image
+	quality that the hardware can deliver. It is not defined how the
+	driver writer may achieve that; it will depend on the hardware and
+	the ingenuity of the driver writer. High quality mode is a
+	different mode from the regular motion video capture modes. In
+	high quality mode:
+
+	-  The driver may be able to capture higher resolutions than for
+	   motion capture.
+
+	-  The driver may support fewer pixel formats than motion capture
+	   (eg; true color).
+
+	-  The driver may capture and arithmetically combine multiple
+	   successive fields or frames to remove color edge artifacts and
+	   reduce the noise in the video data.
+
+	-  The driver may capture images in slices like a scanner in order
+	   to handle larger format images than would otherwise be
+	   possible.
+
+	-  An image capture operation may be significantly slower than
+	   motion capture.
+
+	-  Moving objects in the image might have excessive motion blur.
+
+	-  Capture might only work through the :ref:`read() <func-read>` call.
+
+
+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.