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, 74 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/dev-meta.rst b/Documentation/userspace-api/media/v4l/dev-meta.rst
new file mode 100644
index 000000000000..6d2c5a79b370
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+.. 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
+
+.. _metadata:
+
+******************
+Metadata Interface
+******************
+
+Metadata refers to any non-image data that supplements video frames with
+additional information. This may include statistics computed over the image,
+frame capture parameters supplied by the image source or device specific
+parameters for specifying how the device processes images. This interface is
+intended for transfer of metadata between the userspace and the hardware and
+control of that operation.
+
+The metadata interface is implemented on video device nodes. The device can be
+dedicated to metadata or can support both video and metadata as specified in its
+reported capabilities.
+
+Querying Capabilities
+=====================
+
+Device nodes supporting the metadata capture interface set the
+``V4L2_CAP_META_CAPTURE`` flag in the ``device_caps`` field of the
+:c:type:`v4l2_capability` structure returned by the :c:func:`VIDIOC_QUERYCAP`
+ioctl. That flag means the device can capture metadata to memory. Similarly,
+device nodes supporting metadata output interface set the
+``V4L2_CAP_META_OUTPUT`` flag in the ``device_caps`` field of
+:c:type:`v4l2_capability` structure. That flag means the device can read
+metadata from memory.
+
+At least one of the read/write or streaming I/O methods must be supported.
+
+
+Data Format Negotiation
+=======================
+
+The metadata device uses the :ref:`format` ioctls to select the capture format.
+The metadata buffer content format is bound to that selected format. In addition
+to the basic :ref:`format` ioctls, the :c:func:`VIDIOC_ENUM_FMT` ioctl must be
+supported as well.
+
+To use the :ref:`format` ioctls applications set the ``type`` field of the
+:c:type:`v4l2_format` structure to ``V4L2_BUF_TYPE_META_CAPTURE`` or to
+``V4L2_BUF_TYPE_META_OUTPUT`` and use the :c:type:`v4l2_meta_format` ``meta``
+member of the ``fmt`` union as needed per the desired operation. Both drivers
+and applications must set the remainder of the :c:type:`v4l2_format` structure
+to 0.
+
+.. c:type:: v4l2_meta_format
+
+.. tabularcolumns:: |p{1.4cm}|p{2.2cm}|p{13.9cm}|
+
+.. flat-table:: struct v4l2_meta_format
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``dataformat``
+      - The data format, set by the application. This is a little endian
+        :ref:`four character code <v4l2-fourcc>`. V4L2 defines metadata formats
+        in :ref:`meta-formats`.
+    * - __u32
+      - ``buffersize``
+      - Maximum buffer size in bytes required for data. The value is set by the
+        driver.