[PATCH 07/26] media: Documentation: Add VIDIOC_BIND_CONTEXT

[Jacopo Mondi]

Document the newly introduced VIDIOC_BIND_CONTEXT ioctl.

Signed-off-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
---
 .../userspace-api/media/v4l/user-func.rst          |  1 +
 .../media/v4l/vidioc-bind-context.rst              | 80 ++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
index 6f661138801cde2810997740ee8305085fe73a43..0d9aff56ab653b2a4f6afe4828f88bc5637addf1 100644
--- a/Documentation/userspace-api/media/v4l/user-func.rst
+++ b/Documentation/userspace-api/media/v4l/user-func.rst
@@ -12,6 +12,7 @@ Function Reference
 
     func-close
     func-ioctl
+    vidioc-bind-context
     vidioc-create-bufs
     vidioc-cropcap
     vidioc-dbg-g-chip-info
diff --git a/Documentation/userspace-api/media/v4l/vidioc-bind-context.rst b/Documentation/userspace-api/media/v4l/vidioc-bind-context.rst
new file mode 100644
index 0000000000000000000000000000000000000000..74c885169e22c495056a9364e722e2140d8f21c5
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-bind-context.rst
@@ -0,0 +1,80 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _vidioc_bind_context:
+
+*************************
+ioctl VIDIOC_BIND_CONTEXT
+*************************
+
+Name
+====
+
+VIDIOC_BIND_CONTEXT - Bind a video device file handle to a media device context
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_BIND_CONTEXT
+
+``int ioctl(int fd, VIDIOC_BIND_CONTEXT, struct v4l2_context *argp)``
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :c:func:`open()`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_context`.
+
+Description
+===========
+
+Applications call the ``VIDIOC_BIND_CONTEXT`` ioctl to bind a video device file
+handle to a media device  context. Binding a video device file handle to a media
+device context creates an isolated execution context which allows to multiplex
+the usage of a video device. This means, in practice, that the video device
+configuration (format, sizes etc) applied on a file handle bound to a media
+device context won't be visible on file handles bound to a different media
+device context (or not bound at all).
+
+By opening a media device applications create a media device context to which
+video devices and subdevices file handles can be bound to. The file descriptor
+returned by a call to :c:func:`open()` on the media device identifies uniquely
+the media device context. Application populates the ``context_fd`` field of
+:c:type:`v4l2_context` with the file descriptor of an open media device to
+identify the media context to which they want to bind a video device to.
+
+Applications can open a video device node multiple times, and call
+``VIDIOC_BIND_CONTEXT`` on each file handle returned by a successful call to
+:c:func:`open()` to isolate the operations performed on that file handle from
+any operation performed on other file handles bound to different contexts. This
+means, in example, that the video device format, sizes and the buffers are
+isolated from the ones associated with a file descriptor, obtained by opening
+the same video device but bound to a different media device context (or not
+bound at all).
+
+The bounding operation realizes a permanent association valid until the video
+device context is released by closing the file handle.
+
+A video device file handle can be bound to the same media device context once
+only. Trying to bind the same file handle to the same media device context a
+second time, without releasing the already established context by closing the
+bound file descriptor first, will result in an error.
+
+Bounding is an opt-in feature that applications are free to ignore. Any
+operation directed to a non bound file handle will continue to work as it used
+to, and the video device configuration (formats, sizes etc) will be visible
+across all the other non-bound file handles.
+
+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 media device context file handle ``context_fd`` is not valid or the
+    video device file handle is already bound to a context.

-- 
2.49.0