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-rw-r--r--Documentation/DocBook/media/v4l/dev-event.xml30
-rw-r--r--Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml15
2 files changed, 36 insertions, 9 deletions
diff --git a/Documentation/DocBook/media/v4l/dev-event.xml b/Documentation/DocBook/media/v4l/dev-event.xml
index be5a98fb4fab..f14ae3fe107c 100644
--- a/Documentation/DocBook/media/v4l/dev-event.xml
+++ b/Documentation/DocBook/media/v4l/dev-event.xml
@@ -1,9 +1,10 @@
1 <title>Event Interface</title> 1 <title>Event Interface</title>
2 2
3 <para>The V4L2 event interface provides means for user to get 3 <para>The V4L2 event interface provides a means for a user to get
4 immediately notified on certain conditions taking place on a device. 4 immediately notified on certain conditions taking place on a device.
5 This might include start of frame or loss of signal events, for 5 This might include start of frame or loss of signal events, for
6 example. 6 example. Changes in the value or state of a V4L2 control can also be
7 reported through events.
7 </para> 8 </para>
8 9
9 <para>To receive events, the events the user is interested in first must 10 <para>To receive events, the events the user is interested in first must
@@ -15,12 +16,31 @@
15 16
16 <para>The event subscriptions and event queues are specific to file 17 <para>The event subscriptions and event queues are specific to file
17 handles. Subscribing an event on one file handle does not affect 18 handles. Subscribing an event on one file handle does not affect
18 other file handles. 19 other file handles.</para>
19 </para>
20 20
21 <para>The information on dequeueable events is obtained by using select or 21 <para>The information on dequeueable events is obtained by using select or
22 poll system calls on video devices. The V4L2 events use POLLPRI events on 22 poll system calls on video devices. The V4L2 events use POLLPRI events on
23 poll system call and exceptions on select system call. </para> 23 poll system call and exceptions on select system call.</para>
24
25 <para>Starting with kernel 3.1 certain guarantees can be given with
26 regards to events:<orderedlist>
27 <listitem>
28 <para>Each subscribed event has its own internal dedicated event queue.
29This means that flooding of one event type will not interfere with other
30event types.</para>
31 </listitem>
32 <listitem>
33 <para>If the internal event queue for a particular subscribed event
34becomes full, then the oldest event in that queue will be dropped.</para>
35 </listitem>
36 <listitem>
37 <para>Where applicable, certain event types can ensure that the payload
38of the oldest event that is about to be dropped will be merged with the payload
39of the next oldest event. Thus ensuring that no information is lost, but only an
40intermediate step leading up to that information. See the documentation for the
41event you want to subscribe to whether this is applicable for that event or not.</para>
42 </listitem>
43 </orderedlist></para>
24 44
25 <!-- 45 <!--
26Local Variables: 46Local Variables:
diff --git a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
index 975f603a42ee..039a9694fd1d 100644
--- a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
@@ -100,7 +100,7 @@
100 <entry><constant>V4L2_EVENT_VSYNC</constant></entry> 100 <entry><constant>V4L2_EVENT_VSYNC</constant></entry>
101 <entry>1</entry> 101 <entry>1</entry>
102 <entry>This event is triggered on the vertical sync. 102 <entry>This event is triggered on the vertical sync.
103 This event has &v4l2-event-vsync; associated with it. 103 This event has a &v4l2-event-vsync; associated with it.
104 </entry> 104 </entry>
105 </row> 105 </row>
106 <row> 106 <row>
@@ -118,7 +118,7 @@
118 matches the control ID from which you want to receive events. 118 matches the control ID from which you want to receive events.
119 This event is triggered if the control's value changes, if a 119 This event is triggered if the control's value changes, if a
120 button control is pressed or if the control's flags change. 120 button control is pressed or if the control's flags change.
121 This event has &v4l2-event-ctrl; associated with it. This struct 121 This event has a &v4l2-event-ctrl; associated with it. This struct
122 contains much of the same information as &v4l2-queryctrl; and 122 contains much of the same information as &v4l2-queryctrl; and
123 &v4l2-control;. 123 &v4l2-control;.
124 124
@@ -126,6 +126,13 @@
126 &VIDIOC-S-EXT-CTRLS;, then the event will not be sent to 126 &VIDIOC-S-EXT-CTRLS;, then the event will not be sent to
127 the file handle that called the ioctl function. This prevents 127 the file handle that called the ioctl function. This prevents
128 nasty feedback loops. 128 nasty feedback loops.
129
130 This event type will ensure that no information is lost when
131 more events are raised than there is room internally. In that
132 case the &v4l2-event-ctrl; of the second-oldest event is kept,
133 but the <structfield>changes</structfield> field of the
134 second-oldest event is ORed with the <structfield>changes</structfield>
135 field of the oldest event.
129 </entry> 136 </entry>
130 </row> 137 </row>
131 <row> 138 <row>
@@ -147,8 +154,8 @@
147 <entry>0x0001</entry> 154 <entry>0x0001</entry>
148 <entry>When this event is subscribed an initial event will be sent 155 <entry>When this event is subscribed an initial event will be sent
149 containing the current status. This only makes sense for events 156 containing the current status. This only makes sense for events
150 that are triggered by a status change. Other events will ignore 157 that are triggered by a status change such as <constant>V4L2_EVENT_CTRL</constant>.
151 this flag.</entry> 158 Other events will ignore this flag.</entry>
152 </row> 159 </row>
153 </tbody> 160 </tbody>
154 </tgroup> 161 </tgroup>