linux-kernel - [PATCH v4 2/2] media/Documentation: Volatile writable

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Date:	Tue, 17 Feb 2015 16:09:38 +0100
From:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Jonathan Corbet <corbet@....net>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Arun Kumar K <arun.kk@...sung.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-media@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Subject: [PATCH v4 2/2] media/Documentation: Volatile writable

Volatile variables are also writable now. Update the documentation
accordingly.

Acked-by: Hans Verkuil <hans.verkuil@...co.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
---
v4: Hans Verkuil:
Fix typos and add ack-by Hans

 Documentation/DocBook/media/v4l/vidioc-dqevent.xml   | 7 ++++---
 Documentation/DocBook/media/v4l/vidioc-queryctrl.xml | 6 ++++--
 Documentation/video4linux/v4l2-controls.txt          | 4 +++-
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/Documentation/DocBook/media/v4l/vidioc-dqevent.xml b/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
index b036f89..8ca24c4 100644
--- a/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
@@ -318,9 +318,10 @@
 	    <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
 	    <entry>0x0001</entry>
 	    <entry>This control event was triggered because the value of the control
-		changed. Special case: if a button control is pressed, then this
-		event is sent as well, even though there is not explicit value
-		associated with a button control.</entry>
+		changed. Special cases: volatile controls do not generate this event.
+		If a button control is pressed, then this event is sent as well,
+		even though there is no explicit value associated with a button
+		control.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
diff --git a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
index 2bd98fd..6e1e98d 100644
--- a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
@@ -599,8 +599,10 @@ writing a value will cause the device to carry out a given action
 	    <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>
+the lighting conditions which can change over time. Another example would be an error
+flag (missed trigger, invalid voltage on the sensor). In those situations the user
+could write to the control to acknowledge the error, but that write will never
+generate a <constant>V4L2_EVENT_CTRL_CH_VALUE</constant> event.<entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry>
diff --git a/Documentation/video4linux/v4l2-controls.txt b/Documentation/video4linux/v4l2-controls.txt
index 0f84ce8..5517db6 100644
--- a/Documentation/video4linux/v4l2-controls.txt
+++ b/Documentation/video4linux/v4l2-controls.txt
@@ -344,7 +344,9 @@ implement g_volatile_ctrl like this:
 	}
 
 Note that you use the 'new value' union as well in g_volatile_ctrl. In general
-controls that need to implement g_volatile_ctrl are read-only controls.
+controls that need to implement g_volatile_ctrl are read-only controls. If they
+are not, a V4L2_EVENT_CTRL_CH_VALUE will not be generated when the control
+changes.
 
 To mark a control as volatile you have to set V4L2_CTRL_FLAG_VOLATILE:
 
-- 
2.1.4

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