Hello Hans and Laurent I understand volatile as a control that can change its value by the device. So in that sense I think that my control is volatile and writeable (ack by the user). The value written by the user is meaning-less in my usercase, but in another s it could be useful. I am outside the office and with no computer for the next two weeks. If you can wait until then I can implement Hans idea or another one and try it out with my hw. Thanks for consideing my usercase :) Regards (Sorry for duplicate, still trying to convince my phone to use plain text) On 24 February 2015 06:07:49 GMT+07:00, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: >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(+) -- Ricardo Ribalda Sent from my Android device with K-9 Mail. Please excuse my brevity. -- 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
