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, 108 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-audioout.rst b/Documentation/userspace-api/media/v4l/vidioc-g-audioout.rst
new file mode 100644
index 000000000000..e13b74bf5ce3
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-audioout.rst
@@ -0,0 +1,108 @@
+.. 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_AUDOUT:
+
+**************************************
+ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT
+**************************************
+
+Name
+====
+
+VIDIOC_G_AUDOUT - VIDIOC_S_AUDOUT - Query or select the current audio output
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_G_AUDOUT, struct v4l2_audioout *argp )
+    :name: VIDIOC_G_AUDOUT
+
+.. c:function:: int ioctl( int fd, VIDIOC_S_AUDOUT, const struct v4l2_audioout *argp )
+    :name: VIDIOC_S_AUDOUT
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_audioout`.
+
+
+Description
+===========
+
+To query the current audio output applications zero out the ``reserved``
+array of a struct :c:type:`v4l2_audioout` and call the
+``VIDIOC_G_AUDOUT`` ioctl with a pointer to this structure. Drivers fill
+the rest of the structure or return an ``EINVAL`` error code when the device
+has no audio inputs, or none which combine with the current video
+output.
+
+Audio outputs have no writable properties. Nevertheless, to select the
+current audio output applications can initialize the ``index`` field and
+``reserved`` array (which in the future may contain writable properties)
+of a struct :c:type:`v4l2_audioout` structure and call the
+``VIDIOC_S_AUDOUT`` ioctl. Drivers switch to the requested output or
+return the ``EINVAL`` error code when the index is out of bounds. This is a
+write-only ioctl, it does not return the current audio output attributes
+as ``VIDIOC_G_AUDOUT`` does.
+
+.. note::
+
+   Connectors on a TV card to loop back the received audio signal
+   to a sound card are not audio outputs in this sense.
+
+
+.. c:type:: v4l2_audioout
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. flat-table:: struct v4l2_audioout
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``index``
+      - Identifies the audio output, set by the driver or application.
+    * - __u8
+      - ``name``\ [32]
+      - Name of the audio output, a NUL-terminated ASCII string, for
+	example: "Line Out". This information is intended for the user,
+	preferably the connector label on the device itself.
+    * - __u32
+      - ``capability``
+      - Audio capability flags, none defined yet. Drivers must set this
+	field to zero.
+    * - __u32
+      - ``mode``
+      - Audio mode, none defined yet. Drivers and applications (on
+	``VIDIOC_S_AUDOUT``) must set this field to zero.
+    * - __u32
+      - ``reserved``\ [2]
+      - Reserved for future extensions. Drivers and applications must set
+	the array to zero.
+
+
+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
+    No audio outputs combine with the current video output, or the
+    number of the selected audio output is out of bounds or it does not
+    combine.