Volatile variables are also writable now. Update the documentation accordingly. Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
