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, 67 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-enumaudioout.rst b/Documentation/userspace-api/media/v4l/vidioc-enumaudioout.rst
new file mode 100644
index 000000000000..31c2ae460e2d
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-enumaudioout.rst
@@ -0,0 +1,67 @@
+.. 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_ENUMAUDOUT:
+
+***********************
+ioctl VIDIOC_ENUMAUDOUT
+***********************
+
+Name
+====
+
+VIDIOC_ENUMAUDOUT - Enumerate audio outputs
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_ENUMAUDOUT, struct v4l2_audioout *argp )
+    :name: VIDIOC_ENUMAUDOUT
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_audioout`.
+
+
+Description
+===========
+
+To query the attributes of an audio output applications initialize the
+``index`` field and 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 index is out of
+bounds. To enumerate all audio outputs applications shall begin at index
+zero, incrementing by one until the driver returns ``EINVAL``.
+
+.. note::
+
+    Connectors on a TV card to loop back the received audio signal
+    to a sound card are not audio outputs in this sense.
+
+See :ref:`VIDIOC_G_AUDIOout <VIDIOC_G_AUDOUT>` for a description of struct
+:c:type:`v4l2_audioout`.
+
+
+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 number of the audio output is out of bounds.