path: root/Documentation
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authorHans Verkuil <hans.verkuil@cisco.com>2011-08-26 07:31:13 -0300
committerMauro Carvalho Chehab <mchehab@redhat.com>2011-09-21 09:52:21 -0300
commit74a45790861f659058e8f8b565d98e5a1fdd8440 (patch)
tree753280699fda90996de8006469046876124bea0e /Documentation
parentb57ce4179b502b3f481f7632da20aae3e488e31a (diff)
[media] videodev2.h: add V4L2_CTRL_FLAG_VOLATILE
Add a new VOLATILE control flag that is set for volatile controls. That way applications know whether the value of the control is volatile (i.e. can change continuously) or not. Until now this was an internal property, but it is useful to know in userspace as well. A typical use case is the gain value when autogain is on. In that case the hardware will continuously adjust the gain based various environmental factors. This patch just adds and documents the flag, it's not yet used. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Acked-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'Documentation')
3 files changed, 25 insertions, 1 deletions
diff --git a/Documentation/DocBook/media/v4l/compat.xml b/Documentation/DocBook/media/v4l/compat.xml
index ce1004a7da52..91410b6e7e08 100644
--- a/Documentation/DocBook/media/v4l/compat.xml
+++ b/Documentation/DocBook/media/v4l/compat.xml
@@ -2370,6 +2370,14 @@ that used it. It was originally scheduled for removal in 2.6.35.
+ <section>
+ <title>V4L2 in Linux 3.2</title>
+ <orderedlist>
+ <listitem>
+ <para>V4L2_CTRL_FLAG_VOLATILE was added to signal volatile controls to userspace.</para>
+ </listitem>
+ </orderedlist>
+ </section>
<section id="other">
<title>Relation of V4L2 to other Linux multimedia APIs</title>
diff --git a/Documentation/DocBook/media/v4l/v4l2.xml b/Documentation/DocBook/media/v4l/v4l2.xml
index 0d05e8747c12..40132c277647 100644
--- a/Documentation/DocBook/media/v4l/v4l2.xml
+++ b/Documentation/DocBook/media/v4l/v4l2.xml
@@ -128,6 +128,13 @@ structs, ioctls) must be noted in more detail in the history chapter
applications. -->
+ <revnumber>3.2</revnumber>
+ <date>2011-08-26</date>
+ <authorinitials>hv</authorinitials>
+ <revremark>Added V4L2_CTRL_FLAG_VOLATILE.</revremark>
+ </revision>
+ <revision>
<authorinitials>mcc, po, hv</authorinitials>
@@ -410,7 +417,7 @@ and discussions on the V4L mailing list.</revremark>
<title>Video for Linux Two API Specification</title>
- <subtitle>Revision 3.1</subtitle>
+ <subtitle>Revision 3.2</subtitle>
<chapter id="common">
diff --git a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
index 677ea646c29f..0ac0057a51c4 100644
--- a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
@@ -406,6 +406,15 @@ flag is typically present for relative controls or action controls where
writing a value will cause the device to carry out a given action
(&eg; motor control) but no meaningful value can be returned.</entry>
+ <row>
+ <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry>
+ <entry>0x0080</entry>
+ <entry>This control is volatile, which means that the value of the control
+changes continuously. A typical example would be the current gain value if the device
+is in auto-gain mode. In such a case the hardware calculates the gain value based on
+the lighting conditions which can change over time. Note that setting a new value for
+a volatile control will have no effect. The new value will just be ignored.</entry>
+ </row>

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