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

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("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>

Documentation/userspace-api/media/rc/lirc-read.rst

@@ -0,0 +1,76 @@
+.. 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
+
+.. _lirc-read:
+
+***********
+LIRC read()
+***********
+
+Name
+====
+
+lirc-read - Read from a LIRC device
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <unistd.h>
+
+
+.. c:function:: ssize_t read( int fd, void *buf, size_t count )
+    :name: lirc-read
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by ``open()``.
+
+``buf``
+   Buffer to be filled
+
+``count``
+   Max number of bytes to read
+
+Description
+===========
+
+:ref:`read() <lirc-read>` attempts to read up to ``count`` bytes from file
+descriptor ``fd`` into the buffer starting at ``buf``.  If ``count`` is zero,
+:ref:`read() <lirc-read>` returns zero and has no other results. If ``count``
+is greater than ``SSIZE_MAX``, the result is unspecified.
+
+The exact format of the data depends on what :ref:`lirc_modes` a driver
+uses. Use :ref:`lirc_get_features` to get the supported mode, and use
+:ref:`lirc_set_rec_mode` set the current active mode.
+
+The mode :ref:`LIRC_MODE_MODE2 <lirc-mode-mode2>` is for raw IR,
+in which packets containing an unsigned int value describing an IR signal are
+read from the chardev.
+
+Alternatively, :ref:`LIRC_MODE_SCANCODE <lirc-mode-scancode>` can be available,
+in this mode scancodes which are either decoded by software decoders, or
+by hardware decoders. The :c:type:`rc_proto` member is set to the
+:ref:`IR protocol <Remote_controllers_Protocols>`
+used for transmission, and ``scancode`` to the decoded scancode,
+and the ``keycode`` set to the keycode or ``KEY_RESERVED``.
+
+
+Return Value
+============
+
+On success, the number of bytes read is returned. It is not an error if
+this number is smaller than the number of bytes requested, or the amount
+of data required for one frame.  On error, -1 is returned, and the ``errno``
+variable is set appropriately.