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: <77d91964-de0a-8bd4-12d9-bc16110cfa7c@wolfvision.net>
Date:   Wed, 12 Apr 2023 15:43:26 +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,
        hverkuil@...all.nl
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 14:05, Sakari Ailus wrote:
> 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.

The documentation of which control exactly? And what items should be added?

Thanks for the pointers!

Best regards,
Michael

> 
> Also cc Hans.
>