linux-kernel - Re: [libcamera-devel] [PATCH RFC 1/4] media: v4l2-ctrls: add lens group status controls for zoom and focus

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Message-ID: <ZDaemghP0HQSw3Fo@kekkonen.localdomain>
Date:   Wed, 12 Apr 2023 15:05:46 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Michael Riesch <michael.riesch@...fvision.net>
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Riesch via B4 Relay 
        <devnull+michael.riesch.wolfvision.net@...nel.org>,
        linux-kernel@...r.kernel.org,
        Matthias Fend <Matthias.Fend@...fvision.net>,
        libcamera-devel@...ts.libcamera.org, linux-media@...r.kernel.org,
        hverkuil@...all.nl
Subject: Re: [libcamera-devel] [PATCH RFC 1/4] media: v4l2-ctrls: add lens
 group status controls for zoom and focus

Hi Michael,

On Wed, Apr 12, 2023 at 01:57:36PM +0200, Michael Riesch wrote:
> Hi Sakari,
> 
> On 4/12/23 13:50, Sakari Ailus wrote:
> > Hi Michael,
> > 
> > On Wed, Apr 12, 2023 at 10:00:26AM +0200, Michael Riesch wrote:
> >>  - Different controls: If moving = (V4L2_CID_FOCUS_ABSOLUTE == current),
> >>    then what happens if the application performs a
> >>    V4L2_CID_FOCUS_RELATIVE with -3? current should reach 39,
> >>    V4L2_CID_FOCUS_ABSOLUTE is still at 42, the lens is still moving from
> >>    the application's point of view.
> > 
> > Would there be a reason to implement both of these controls in a single
> > driver? AFAIU, the relative one should be used if there absolute value
> > isn't known to the driver.
> 
> Probably not, but on the other hand there is nothing the prevents a
> driver developer from doing so, right? Point is that should there be a
> driver which does implement both controls, we are in trouble AFAIU.

I think the documentation should be improved in this regard.

Also cc Hans.

-- 
Regards,

Sakari Ailus