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, 120 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-interval.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-interval.rst
new file mode 100644
index 000000000000..3527745935c7
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-interval.rst
@@ -0,0 +1,120 @@
+.. 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_ENUM_FRAME_INTERVAL:
+
+***************************************
+ioctl VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL
+***************************************
+
+Name
+====
+
+VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL - Enumerate frame intervals
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL, struct v4l2_subdev_frame_interval_enum * argp )
+    :name: VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_subdev_frame_interval_enum`.
+
+
+Description
+===========
+
+This ioctl lets applications enumerate available frame intervals on a
+given sub-device pad. Frame intervals only makes sense for sub-devices
+that can control the frame period on their own. This includes, for
+instance, image sensors and TV tuners.
+
+For the common use case of image sensors, the frame intervals available
+on the sub-device output pad depend on the frame format and size on the
+same pad. Applications must thus specify the desired format and size
+when enumerating frame intervals.
+
+To enumerate frame intervals applications initialize the ``index``,
+``pad``, ``which``, ``code``, ``width`` and ``height`` fields of struct
+:c:type:`v4l2_subdev_frame_interval_enum`
+and call the :ref:`VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL` ioctl with a pointer
+to this structure. Drivers fill the rest of the structure or return an
+EINVAL error code if one of the input fields is invalid. All frame
+intervals are enumerable by beginning at index zero and incrementing by
+one until ``EINVAL`` is returned.
+
+Available frame intervals may depend on the current 'try' formats at
+other pads of the sub-device, as well as on the current active links.
+See :ref:`VIDIOC_SUBDEV_G_FMT` for more
+information about the try formats.
+
+Sub-devices that support the frame interval enumeration ioctl should
+implemented it on a single pad only. Its behaviour when supported on
+multiple pads of the same sub-device is not defined.
+
+.. c:type:: v4l2_subdev_frame_interval_enum
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. flat-table:: struct v4l2_subdev_frame_interval_enum
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``index``
+      - Number of the format in the enumeration, set by the application.
+    * - __u32
+      - ``pad``
+      - Pad number as reported by the media controller API.
+    * - __u32
+      - ``code``
+      - The media bus format code, as defined in
+	:ref:`v4l2-mbus-format`.
+    * - __u32
+      - ``width``
+      - Frame width, in pixels.
+    * - __u32
+      - ``height``
+      - Frame height, in pixels.
+    * - struct :c:type:`v4l2_fract`
+      - ``interval``
+      - Period, in seconds, between consecutive video frames.
+    * - __u32
+      - ``which``
+      - Frame intervals to be enumerated, from enum
+	:ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
+    * - __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.
+
+EINVAL
+    The struct
+    :c:type:`v4l2_subdev_frame_interval_enum`
+    ``pad`` references a non-existing pad, one of the ``code``,
+    ``width`` or ``height`` fields are invalid for the given pad or the
+    ``index`` field is out of bounds.