From 871480933a1c28f8a9fed4c4d34d06c439a7a422 Mon Sep 17 00:00:00 2001
From: Srikant Patnaik
Date: Sun, 11 Jan 2015 12:28:04 +0530
Subject: Moved, renamed, and deleted files

The original directory structure was scattered and unorganized.
Changes are basically to make it look like kernel structure.
---
 Documentation/DocBook/media/v4l/dev-event.xml | 43 +++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 Documentation/DocBook/media/v4l/dev-event.xml

(limited to 'Documentation/DocBook/media/v4l/dev-event.xml')

diff --git a/Documentation/DocBook/media/v4l/dev-event.xml b/Documentation/DocBook/media/v4l/dev-event.xml
new file mode 100644
index 00000000..19f4becf
--- /dev/null
+++ b/Documentation/DocBook/media/v4l/dev-event.xml
@@ -0,0 +1,43 @@
+  <title>Event Interface</title>
+
+  <para>The V4L2 event interface provides a means for a user to get
+  immediately notified on certain conditions taking place on a device.
+  This might include start of frame or loss of signal events, for
+  example. Changes in the value or state of a V4L2 control can also be
+  reported through events.
+  </para>
+
+  <para>To receive events, the events the user is interested in first must
+  be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
+  subscribed, the events of subscribed types are dequeueable using the
+  &VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
+  VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
+  be used to unsubscribe all the events the driver supports.</para>
+
+  <para>The event subscriptions and event queues are specific to file
+  handles. Subscribing an event on one file handle does not affect
+  other file handles.</para>
+
+  <para>The information on dequeueable events is obtained by using select or
+  poll system calls on video devices. The V4L2 events use POLLPRI events on
+  poll system call and exceptions on select system call.</para>
+
+  <para>Starting with kernel 3.1 certain guarantees can be given with
+  regards to events:<orderedlist>
+	<listitem>
+	  <para>Each subscribed event has its own internal dedicated event queue.
+This means that flooding of one event type will not interfere with other
+event types.</para>
+	</listitem>
+	<listitem>
+	  <para>If the internal event queue for a particular subscribed event
+becomes full, then the oldest event in that queue will be dropped.</para>
+	</listitem>
+	<listitem>
+	  <para>Where applicable, certain event types can ensure that the payload
+of the oldest event that is about to be dropped will be merged with the payload
+of the next oldest event. Thus ensuring that no information is lost, but only an
+intermediate step leading up to that information. See the documentation for the
+event you want to subscribe to whether this is applicable for that event or not.</para>
+	</listitem>
+      </orderedlist></para>
-- 
cgit