Messages in this thread |  | | Date | Tue, 17 Feb 2015 13:03:29 +0100 | From | Hans Verkuil <> | Subject | Re: [PATCH] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls |
| |
Hi Ricardo,
I've thought about this some more and I agree that this should be allowed.
But I have some comments, see below.
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. > > 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;
Should be done after the 'ctrl == NULL' check.
> > if (ctrl == NULL) > continue; >
There is one more change that has to be made: setting a volatile control should never generate a V4L2_EVENT_CTRL_CH_VALUE event since that makes no sense. The way to prevent that is to ensure that ctrl->has_changed is always false for volatile controls. The new_to_cur function looks at that field to decide whether to send an event.
The documentation should also be updated: that of V4L2_CTRL_FLAG_VOLATILE (in VIDIOC_QUERYCTRL), and of V4L2_EVENT_CTRL_CH_VALUE.
Regards,
Hans
|  |