Hi Hans, On Monday 23 February 2015 10:06:10 Hans Verkuil wrote: > On 02/17/2015 04:08 PM, 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. > > I've been thinking some more about this (also due to some comments Laurent > made on irc), and I think this should be done differently. > > What you want to do here is to signal that setting this control will execute > some action that needs to happen even if the same value is set twice. > > That's not really covered by VOLATILE. Interestingly, the WRITE_ONLY flag is > to be used for just that purpose, but this happens to be a R/W control, so > that can't be used either. > > What is needed is the following: > > 1) Add a new flag: V4L2_CTRL_FLAG_ACTION. > 2) Any control that sets FLAG_WRITE_ONLY should OR it with FLAG_ACTION (to > keep the current meaning of WRITE_ONLY). > 3) Any control with FLAG_ACTION set should return changed == true in > cluster_changed. > 4) Any control with FLAG_VOLATILE set should set ctrl->has_changed to false > to prevent generating the CH_VALUE control (that's a real bug). > > Your control will now set FLAG_ACTION and FLAG_VOLATILE and it will do the > right thing. I'm not sure about Ricardo's use case, is it the one we've discussed on #v4l ? If so, and if I recall correctly, the idea was to perform an action with a parameter, and didn't require volatility. > Basically what was missing was a flag to explicitly signal this 'writing > executes an action' behavior. Trying to shoehorn that into the volatile > flag or the write_only flag is just not right. It's a flag in its own right. Just for the sake of exploring all options, what did you think about the idea of making button controls accept a value ? Your proposal is interesting as well, but I'm not sure about the V4L2_CTRL_FLAG_ACTION name. Aren't all controls supposed to have an action of some sort ? That's nitpicking of course. Also, should the action flag be automatically set for button controls ? Button controls would in a way become type-less controls with the action flag set, that's interesting. I suppose type-less controls without the action flag don't make sense. > > Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx> > > --- > > v4: Hans Verkuil: > > > > explicity set has_changed to false. and add comment > > > > drivers/media/v4l2-core/v4l2-ctrls.c | 11 +++++++++++ > > 1 file changed, 11 insertions(+) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
