Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 116 insertions, 0 deletions

diff --git a/Documentation/media/uapi/v4l/vidioc-subscribe-event.rst b/Documentation/media/uapi/v4l/vidioc-subscribe-event.rst
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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_SUBSCRIBE_EVENT:
+.. _VIDIOC_UNSUBSCRIBE_EVENT:
+
+******************************************************
+ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT
+******************************************************
+
+Name
+====
+
+VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBSCRIBE_EVENT, struct v4l2_event_subscription *argp )
+    :name: VIDIOC_SUBSCRIBE_EVENT
+
+.. c:function:: int ioctl( int fd, VIDIOC_UNSUBSCRIBE_EVENT, struct v4l2_event_subscription *argp )
+    :name: VIDIOC_UNSUBSCRIBE_EVENT
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_event_subscription`.
+
+
+Description
+===========
+
+Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by
+using the :ref:`VIDIOC_DQEVENT` ioctl.
+
+
+.. tabularcolumns:: |p{4.6cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_event_subscription
+
+.. flat-table:: struct v4l2_event_subscription
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``type``
+      - Type of the event, see :ref:`event-type`.
+
+	.. note::
+
+	   ``V4L2_EVENT_ALL`` can be used with
+	   :ref:`VIDIOC_UNSUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` for
+	   unsubscribing all events at once.
+    * - __u32
+      - ``id``
+      - ID of the event source. If there is no ID associated with the
+	event source, then set this to 0. Whether or not an event needs an
+	ID depends on the event type.
+    * - __u32
+      - ``flags``
+      - Event flags, see :ref:`event-flags`.
+    * - __u32
+      - ``reserved``\ [5]
+      - Reserved for future extensions. Drivers and applications must set
+	the array to zero.
+
+
+
+.. tabularcolumns:: |p{6.8cm}|p{2.2cm}|p{8.5cm}|
+
+.. _event-flags:
+
+.. flat-table:: Event Flags
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+    * - ``V4L2_EVENT_SUB_FL_SEND_INITIAL``
+      - 0x0001
+      - When this event is subscribed an initial event will be sent
+	containing the current status. This only makes sense for events
+	that are triggered by a status change such as ``V4L2_EVENT_CTRL``.
+	Other events will ignore this flag.
+    * - ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
+      - 0x0002
+      - If set, then events directly caused by an ioctl will also be sent
+	to the filehandle that called that ioctl. For example, changing a
+	control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause
+	a V4L2_EVENT_CTRL to be sent back to that same filehandle.
+	Normally such events are suppressed to prevent feedback loops
+	where an application changes a control to a one value and then
+	another, and then receives an event telling it that that control
+	has changed to the first value.
+
+	Since it can't tell whether that event was caused by another
+	application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>`
+	call it is hard to decide whether to set the control to the value
+	in the event, or ignore it.
+
+	Think carefully when you set this flag so you won't get into
+	situations like that.
+
+
+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.