linux-kernel - Re: [PATCH RFC v2 2/6] media: v4l2-ctrls: clarify documentation of V4L2_CID_FOCUS

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Date:   Tue, 6 Jun 2023 15:15:33 +0200
From:   Michael Riesch <michael.riesch@...fvision.net>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        libcamera-devel@...ts.libcamera.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Matthias Fend <Matthias.Fend@...fvision.net>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/6] media: v4l2-ctrls: clarify documentation of
 V4L2_CID_FOCUS_RELATIVE

Hi Laurent,

On 6/6/23 12:36, Laurent Pinchart wrote:
> Hi Michael,
> 
> Thank you for the patch.
> 
> On Tue, Apr 25, 2023 at 11:45:12AM +0200, Michael Riesch wrote:
>> The control V4L2_CID_FOCUS_RELATIVE only makes sense if the device cannot
>> handle absolute focal point positioning with V4L2_CID_FOCUS_ABSOLUTE.
>> Clarify this in the documentation.
>>
>> Signed-off-by: Michael Riesch <michael.riesch@...fvision.net>
>> ---
>>  Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> index df29150dce7b..42cf4c3cda0c 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> @@ -147,7 +147,9 @@ enum v4l2_exposure_metering -
>>      This control moves the focal point of the camera by the specified
>>      amount. The unit is undefined. Positive values move the focus closer
>>      to the camera, negative values towards infinity. This is a
>> -    write-only control.
>> +    write-only control. It should be implemented only if the device cannot
>> +    handle absolute values.
>> +
> 
> Extra blank line.

Will fix that.

> I don't think this is right. The control was added for the UVC driver,
> and there are devices that implement both absolute and relative focus.

I am by no means an expert here and just following Sakari's suggestion
here (see [0]). I can drop the patch, leave it as-is, or modify it.
Whatever makes sense to you guys. But maybe I should leave this to
someone more knowledgeable in this area and drop the patch from my
series. The changes above are completely orthogonal to my work.

Best regards,
Michael

> 
>>  
>>  ``V4L2_CID_FOCUS_AUTO (boolean)``
>>      Enables continuous automatic focus adjustments. The effect of manual
>>
> 

[0] https://lore.kernel.org/all/ZDbChgZJHVaaX3%2Fx@kekkonen.localdomain/