Document new flag V4L2_CTRL_FLAG_EXECUTE_ON_WRITE, and the new behavior
of CH_VALUE event on VOLATILE controls.
Signed-off-by: Ricardo Ribalda Delgado <ricardo.riba...@gmail.com>
---
Documentation/DocBook/media/v4l/vidioc-dqevent.xml | 7 ++++---
Documentation/DocBook/media/v4l/vidioc-queryctrl.xml | 15 +++++++++++++--
Documentation/video4linux/v4l2-controls.txt | 4 +++-
3 files changed, 20 insertions(+), 6 deletions(-)
diff --git a/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
b/Documentation/DocBook/media/v4l/vidioc-dqevent.xml
index b036f89..38d907e 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 no generate this
event;
+ 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>
</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..d389292 100644
--- a/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml
@@ -599,8 +599,11 @@ 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 and the flag
+<constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant> must be set.<entry>
</row>
<row>
<entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry>
@@ -610,6 +613,14 @@ using one of the pointer fields of &v4l2-ext-control;.
This flag is set for cont
that are an array, string, or have a compound type. In all cases you have to
set a
pointer to memory containing the payload of the control.</entry>
</row>
+ <row>
+ <entry><constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant></entry>
+ <entry>0x0200</entry>
+ <entry>The value provided to the control will be propagated to the
driver
+even if remains constant. This is required when the controls represents an
action
+on the hardware. For example: clearing an error flag or triggering the flash.
All the
+controls of the type <constant>V4L2_CTRL_TYPE_BUTTON</constant> have this flag
set.</entry>
+ </row>
</tbody>
</tgroup>
</table>
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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