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, 106 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
new file mode 100644
index 000000000000..9831b7514028
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
@@ -0,0 +1,106 @@
+.. 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_CTRL:
+
+**********************************
+ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
+**********************************
+
+Name
+====
+
+VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_G_CTRL, struct v4l2_control *argp )
+    :name: VIDIOC_G_CTRL
+
+.. c:function:: int ioctl( int fd, VIDIOC_S_CTRL, struct v4l2_control *argp )
+    :name: VIDIOC_S_CTRL
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_control`.
+
+
+Description
+===========
+
+To get the current value of a control applications initialize the ``id``
+field of a struct :c:type:`v4l2_control` and call the
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
+value of a control applications initialize the ``id`` and ``value``
+fields of a struct :c:type:`v4l2_control` and call the
+:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
+
+When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
+``value`` is out of bounds drivers can choose to take the closest valid
+value or return an ``ERANGE`` error code, whatever seems more appropriate.
+However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
+actual new value. If the ``value`` is inappropriate for the control
+(e.g. if it refers to an unsupported menu index of a menu control), then
+EINVAL error code is returned as well.
+
+These ioctls work only with user controls. For other control classes the
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
+:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
+:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
+
+
+.. c:type:: v4l2_control
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. flat-table:: struct v4l2_control
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``id``
+      - Identifies the control, set by the application.
+    * - __s32
+      - ``value``
+      - New value or current value.
+
+
+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 struct :c:type:`v4l2_control` ``id`` is invalid
+    or the ``value`` is inappropriate for the given control (i.e. if a
+    menu item is selected that is not supported by the driver according
+    to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
+
+ERANGE
+    The struct :c:type:`v4l2_control` ``value`` is out of
+    bounds.
+
+EBUSY
+    The control is temporarily not changeable, possibly because another
+    applications took over control of the device function this control
+    belongs to.
+
+EACCES
+    Attempt to set a read-only control or to get a write-only control.