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Date: Mon, 16 Mar 2015 12:05:05 +0100
From: Hans Verkuil <hverkuil@xs4all.nl>
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To: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
CC: Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
        Hans Verkuil <hans.verkuil@cisco.com>,
        Sylwester Nawrocki <s.nawrocki@samsung.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Antti Palosaari <crope@iki.fi>,
        linux-media <linux-media@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 1/2] media/v4l2-ctrls: Always run s_ctrl on volatile
 ctrls
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On 03/09/2015 05:45 PM, Ricardo Ribalda Delgado wrote:
> Hello
> 
> Back from holidays and back to this issue. Sorry for the delay.
> 
>> 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.
> 
> In my case, there is a trigger overflow bit. The user acks the trigger
> overflow by writting any value to the control.
> 
> There is no parameter. In that sense it looks like a volatile read + a
> button on a controll.
> 
>> 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.

Actually, usually controls just set some parameter and if the new value is
the same as the old value, then nothing is done at all.

A button control always executes some action immediately.

> 
> What about the name STATELESS_WRITE ? or perhaps VOLATILE_WRITE? I
> dont care about the name :), but better have it solved before I write
> the doc :P

How about: ACT_ON_WRITE or EXECUTE_ON_WRITE?

> 
>>
>> 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.

Yes, this flag will be set for button controls. Those are already WRITE_ONLY and
all WRITE_ONLY controls will set the new flag as well.

Regards,

	Hans