Re: [PATCH v4 1/2] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls

From: Ricardo Ribalda Delgado
Date: Mon Feb 23 2015 - 20:05:02 EST

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 :)


(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
>> > 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
>> 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
>> 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
>> 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
>> 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
>> executes an action' behavior. Trying to shoehorn that into the
>> flag or the write_only flag is just not right. It's a flag in its own
>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 ?
>controls would in a way become type-less controls with the action flag
>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
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