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, 125 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-selection.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-selection.rst
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index 000000000000..981c95df2dec
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@@ -0,0 +1,125 @@
+.. 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_SUBDEV_G_SELECTION:
+
+**********************************************************
+ioctl VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION
+**********************************************************
+
+Name
+====
+
+VIDIOC_SUBDEV_G_SELECTION - VIDIOC_SUBDEV_S_SELECTION - Get or set selection rectangles on a subdev pad
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_SELECTION, struct v4l2_subdev_selection *argp )
+    :name: VIDIOC_SUBDEV_G_SELECTION
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_SELECTION, struct v4l2_subdev_selection *argp )
+    :name: VIDIOC_SUBDEV_S_SELECTION
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_subdev_selection`.
+
+
+Description
+===========
+
+The selections are used to configure various image processing
+functionality performed by the subdevs which affect the image size. This
+currently includes cropping, scaling and composition.
+
+The selection API replaces
+:ref:`the old subdev crop API <VIDIOC_SUBDEV_G_CROP>`. All the
+function of the crop API, and more, are supported by the selections API.
+
+See :ref:`subdev` for more information on how each selection target
+affects the image processing pipeline inside the subdevice.
+
+
+Types of selection targets
+--------------------------
+
+There are two types of selection targets: actual and bounds. The actual
+targets are the targets which configure the hardware. The BOUNDS target
+will return a rectangle that contain all possible actual rectangles.
+
+
+Discovering supported features
+------------------------------
+
+To discover which targets are supported, the user can perform
+``VIDIOC_SUBDEV_G_SELECTION`` on them. Any unsupported target will
+return ``EINVAL``.
+
+Selection targets and flags are documented in
+:ref:`v4l2-selections-common`.
+
+
+.. c:type:: v4l2_subdev_selection
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. flat-table:: struct v4l2_subdev_selection
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``which``
+      - Active or try selection, from enum
+	:ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
+    * - __u32
+      - ``pad``
+      - Pad number as reported by the media framework.
+    * - __u32
+      - ``target``
+      - Target selection rectangle. See :ref:`v4l2-selections-common`.
+    * - __u32
+      - ``flags``
+      - Flags. See :ref:`v4l2-selection-flags`.
+    * - struct :c:type:`v4l2_rect`
+      - ``r``
+      - Selection rectangle, in pixels.
+    * - __u32
+      - ``reserved``\ [8]
+      - Reserved for future extensions. Applications and drivers 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.
+
+EBUSY
+    The selection rectangle can't be changed because the pad is
+    currently busy. This can be caused, for instance, by an active video
+    stream on the pad. The ioctl must not be retried without performing
+    another action to fix the problem first. Only returned by
+    ``VIDIOC_SUBDEV_S_SELECTION``
+
+EINVAL
+    The struct :c:type:`v4l2_subdev_selection`
+    ``pad`` references a non-existing pad, the ``which`` field
+    references a non-existing format, or the selection target is not
+    supported on the given subdev pad.