V4L/DVB: V4L: Events: Add documentation

Add documentation on how to use V4L2 events, both for V4L2 drivers and for
V4L2 applications.

Signed-off-by: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

4 files changed, 262 insertions, 0 deletions

diff --git a/Documentation/DocBook/v4l/dev-event.xml b/Documentation/DocBook/v4l/dev-event.xml
new file mode 100644
index 000000000000..be5a98fb4fab
--- /dev/null
+++ b/Documentation/DocBook/v4l/dev-event.xml
@@ -0,0 +1,31 @@
+  <title>Event Interface</title>
+
+  <para>The V4L2 event interface provides means for 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.
+  </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>
+
+  <!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+  -->
diff --git a/Documentation/DocBook/v4l/v4l2.xml b/Documentation/DocBook/v4l/v4l2.xml
index 060105af49e5..9737243377a3 100644
--- a/Documentation/DocBook/v4l/v4l2.xml
+++ b/Documentation/DocBook/v4l/v4l2.xml
@@ -401,6 +401,7 @@ and discussions on the V4L mailing list.</revremark>
     <section id="ttx"> &sub-dev-teletext; </section>
     <section id="radio"> &sub-dev-radio; </section>
     <section id="rds"> &sub-dev-rds; </section>
+    <section id="event"> &sub-dev-event; </section>
   </chapter>
 
   <chapter id="driver">
@@ -426,6 +427,7 @@ and discussions on the V4L mailing list.</revremark>
     &sub-cropcap;
     &sub-dbg-g-chip-ident;
     &sub-dbg-g-register;
+    &sub-dqevent;
     &sub-encoder-cmd;
     &sub-enumaudio;
     &sub-enumaudioout;
@@ -467,6 +469,7 @@ and discussions on the V4L mailing list.</revremark>
     &sub-reqbufs;
     &sub-s-hw-freq-seek;
     &sub-streamon;
+    &sub-subscribe-event;
     <!-- End of ioctls. -->
     &sub-mmap;
     &sub-munmap;
diff --git a/Documentation/DocBook/v4l/vidioc-dqevent.xml b/Documentation/DocBook/v4l/vidioc-dqevent.xml
new file mode 100644
index 000000000000..eb45c1695d8c
--- /dev/null
+++ b/Documentation/DocBook/v4l/vidioc-dqevent.xml
@@ -0,0 +1,124 @@
+<refentry id="vidioc-dqevent">
+  <refmeta>
+    <refentrytitle>ioctl VIDIOC_DQEVENT</refentrytitle>
+    &manvol;
+  </refmeta>
+
+  <refnamediv>
+    <refname>VIDIOC_DQEVENT</refname>
+    <refpurpose>Dequeue event</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcprototype>
+        <funcdef>int <function>ioctl</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>int <parameter>request</parameter></paramdef>
+        <paramdef>struct v4l2_event
+*<parameter>argp</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Arguments</title>
+
+    <variablelist>
+      <varlistentry>
+        <term><parameter>fd</parameter></term>
+        <listitem>
+          <para>&fd;</para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><parameter>request</parameter></term>
+        <listitem>
+          <para>VIDIOC_DQEVENT</para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><parameter>argp</parameter></term>
+        <listitem>
+          <para></para>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>Dequeue an event from a video device. No input is required
+    for this ioctl. All the fields of the &v4l2-event; structure are
+    filled by the driver. The file handle will also receive exceptions
+    which the application may get by e.g. using the select system
+    call.</para>
+
+    <table frame="none" pgwide="1" id="v4l2-event">
+      <title>struct <structname>v4l2_event</structname></title>
+      <tgroup cols="4">
+        &cs-str;
+        <tbody valign="top">
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>type</structfield></entry>
+            <entry></entry>
+            <entry>Type of the event.</entry>
+          </row>
+          <row>
+            <entry>union</entry>
+            <entry><structfield>u</structfield></entry>
+            <entry></entry>
+            <entry></entry>
+          </row>
+          <row>
+            <entry></entry>
+            <entry>__u8</entry>
+            <entry><structfield>data</structfield>[64]</entry>
+            <entry>Event data. Defined by the event type. The union
+            should be used to define easily accessible type for
+            events.</entry>
+          </row>
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>pending</structfield></entry>
+            <entry></entry>
+            <entry>Number of pending events excluding this one.</entry>
+          </row>
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>sequence</structfield></entry>
+            <entry></entry>
+            <entry>Event sequence number. The sequence number is
+            incremented for every subscribed event that takes place.
+            If sequence numbers are not contiguous it means that
+            events have been lost.
+            </entry>
+          </row>
+          <row>
+            <entry>struct timeval</entry>
+            <entry><structfield>timestamp</structfield></entry>
+            <entry></entry>
+            <entry>Event timestamp.</entry>
+          </row>
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>reserved</structfield>[9]</entry>
+            <entry></entry>
+            <entry>Reserved for future extensions. Drivers must set
+            the array to zero.</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+  </refsect1>
+</refentry>
+<!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+-->
diff --git a/Documentation/DocBook/v4l/vidioc-subscribe-event.xml b/Documentation/DocBook/v4l/vidioc-subscribe-event.xml
new file mode 100644
index 000000000000..71ab88cb76b3
--- /dev/null
+++ b/Documentation/DocBook/v4l/vidioc-subscribe-event.xml
@@ -0,0 +1,104 @@
+<refentry id="vidioc-subscribe-event">
+  <refmeta>
+    <refentrytitle>ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refentrytitle>
+    &manvol;
+  </refmeta>
+
+  <refnamediv>
+    <refname>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refname>
+    <refpurpose>Subscribe or unsubscribe event</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcprototype>
+        <funcdef>int <function>ioctl</function></funcdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>int <parameter>request</parameter></paramdef>
+        <paramdef>struct v4l2_event_subscription
+*<parameter>argp</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Arguments</title>
+
+    <variablelist>
+      <varlistentry>
+        <term><parameter>fd</parameter></term>
+        <listitem>
+          <para>&fd;</para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><parameter>request</parameter></term>
+        <listitem>
+          <para>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><parameter>argp</parameter></term>
+        <listitem>
+          <para></para>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>Subscribe or unsubscribe V4L2 event. Subscribed events are
+    dequeued by using the &VIDIOC-DQEVENT; ioctl.</para>
+
+    <table frame="none" pgwide="1" id="v4l2-event-subscription">
+      <title>struct <structname>v4l2_event_subscription</structname></title>
+      <tgroup cols="3">
+        &cs-str;
+        <tbody valign="top">
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>type</structfield></entry>
+            <entry>Type of the event.</entry>
+          </row>
+          <row>
+            <entry>__u32</entry>
+            <entry><structfield>reserved</structfield>[7]</entry>
+            <entry>Reserved for future extensions. Drivers and applications
+            must set the array to zero.</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+    <table frame="none" pgwide="1" id="event-type">
+      <title>Event Types</title>
+      <tgroup cols="3">
+        &cs-def;
+        <tbody valign="top">
+          <row>
+            <entry><constant>V4L2_EVENT_ALL</constant></entry>
+            <entry>0</entry>
+            <entry>All events. V4L2_EVENT_ALL is valid only for
+            VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
+            </entry>
+          </row>
+          <row>
+            <entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
+            <entry>0x08000000</entry>
+            <entry>Base event number for driver-private events.</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+  </refsect1>
+</refentry>
+<!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+-->