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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Date:   Wed, 12 Apr 2023 13:57:36 +0200
From:   Michael Riesch <michael.riesch@...fvision.net>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
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
Subject: Re: [libcamera-devel] [PATCH RFC 1/4] media: v4l2-ctrls: add lens
 group status controls for zoom and focus

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.

Best regards,
Michael