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-write.rst

@@ -0,0 +1,82 @@
+.. 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-write:
+
+************
+LIRC write()
+************
+
+Name
+====
+
+lirc-write - Write to a LIRC device
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <unistd.h>
+
+
+.. c:function:: ssize_t write( int fd, void *buf, size_t count )
+    :name: lirc-write
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by ``open()``.
+
+``buf``
+    Buffer with data to be written
+
+``count``
+    Number of bytes at the buffer
+
+Description
+===========
+
+:ref:`write() <lirc-write>` writes up to ``count`` bytes to the device
+referenced by the file descriptor ``fd`` from the buffer starting at
+``buf``.
+
+The exact format of the data depends on what mode a driver is in, use
+:ref:`lirc_get_features` to get the supported modes and use
+:ref:`lirc_set_send_mode` set the mode.
+
+When in :ref:`LIRC_MODE_PULSE <lirc-mode-PULSE>` mode, the data written to
+the chardev is a pulse/space sequence of integer values. Pulses and spaces
+are only marked implicitly by their position. The data must start and end
+with a pulse, therefore, the data must always include an uneven number of
+samples. The write function blocks until the data has been transmitted
+by the hardware. If more data is provided than the hardware can send, the
+driver returns ``EINVAL``.
+
+When in :ref:`LIRC_MODE_SCANCODE <lirc-mode-scancode>` mode, one
+``struct lirc_scancode`` must be written to the chardev at a time, else
+``EINVAL`` is returned. Set the desired scancode in the ``scancode`` member,
+and the :ref:`IR protocol <Remote_controllers_Protocols>` in the
+:c:type:`rc_proto`: member. All other members must be
+set to 0, else ``EINVAL`` is returned. If there is no protocol encoder
+for the protocol or the scancode is not valid for the specified protocol,
+``EINVAL`` is returned. The write function blocks until the scancode
+is transmitted by the hardware.
+
+
+Return Value
+============
+
+On success, the number of bytes written 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. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.