Messages in this thread |  | | Date | Tue, 17 Feb 2015 12:17:44 +0100 | From | Hans Verkuil <> | Subject | Re: [PATCH] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls |
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Hi Ricardo,
On 02/17/15 12:02, Ricardo Ribalda Delgado wrote: > 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 <ricardo.ribalda@gmail.com> > --- > > 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.
Does the application just read the control to check whether the trigger happened? Or is the control perhaps changed by an interrupt handler?
> The user writes 0 to the control, to ack the error condition, and clear the > hardware flag.
Would it be an idea to automatically ack the error condition when reading the control?
Or, alternatively, have a separate button control to clear the condition.
> > 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.
The reason for that is that I have yet to see a convincing argument for allowing s_ctrl for a volatile control.
Regards,
Hans
> > 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) > continue; >
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