Messages in this thread |  | | Date | Tue, 17 Feb 2015 14:53:27 +0100 | From | Jacek Anaszewski <> | Subject | Re: [PATCH] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls |
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Hi Hans, Sakari,
On 02/17/2015 12:32 PM, Sakari Ailus wrote: > Hi Hans, > > Hans Verkuil wrote: > ... >>> 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. > > Well, one example are LED flash class devices which implement V4L2 flash > API through a wrapper. The user may use the LED flash class API to > change the values of the controls, and V4L2 framework has no clue about > this. The V4L2 controls are volatile, and the real values of the > settings are stored in the LED flash class. > > This is the current implementation (not merged yet); an alternative, a > more correct one, would be to use callbacks to tell about the changes in > control values. I haven't pushed for that, primarily because the > patchset is already quite complex and I've seen this as something that > can be always implemented later if it bothers someone. > > Cc Jacek. >
Actually this will be not an issue for v4l2-flash sub-device anymore. In the next version of the patch set the v4l2-flash sub-device will be synchronizing the flash device registers with the state of the controls on open.
-- Best Regards, Jacek Anaszewski
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