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Subject[PATCH] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls
Volatile controls can change their value outside the v4l-ctrl framework.

We should ignore the cached written value of the ctrl when evaluating if
we should run s_ctrl.

Signed-off-by: Ricardo Ribalda Delgado <>

I have a control that tells the user when there has been a external trigger
overrun. (Trigger while processing old image). This is a volatile control.

The user writes 0 to the control, to ack the error condition, and clear the
hardware flag.

Unfortunately, it only works one time, because the next time the user writes
a zero to the control cluster_changed returns false.

I think on volatile controls it is safer to run s_ctrl twice than missing a
valid s_ctrl.

I know I am abusing a bit the API for this :P, but I also believe that the
semantic here is a bit confusing.

drivers/media/v4l2-core/v4l2-ctrls.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index 45c5b47..3d0c7f4 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -1605,7 +1605,7 @@ static int cluster_changed(struct v4l2_ctrl *master)

for (i = 0; i < master->ncontrols; i++) {
struct v4l2_ctrl *ctrl = master->cluster[i];
- bool ctrl_changed = false;
+ bool ctrl_changed = ctrl->flags & V4L2_CTRL_FLAG_VOLATILE;

if (ctrl == NULL)

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