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: <CAPY8ntCH7JGoKhF2igXUb1WKQgq+rppVjcqUds=oz-TOzL8uWg@mail.gmail.com>
Date:   Wed, 12 Apr 2023 15:57:41 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Michael Riesch <michael.riesch@...fvision.net>,
        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 Wed, 12 Apr 2023 at 15:39, Sakari Ailus <sakari.ailus@...ux.intel.com> wrote:
>
> Hi Michael,
>
> On Wed, Apr 12, 2023 at 03:43:26PM +0200, Michael Riesch wrote:
> > 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?
>
> Both V4L2_CID_FOCUS_ABSOLUTE and V4L2_CID_FOCUS_RELATIVE. For the former,
> the sentence "Positive values set the focus closer to the camera, negative
> values towards infinity." doesn't make much sense in the context. For the
> latter, what I mentioned earlier, i.e. this should be only implemented if
> the absolute value isn't known. It's not a driver's job to do simple
> arithmetics for the user space.
>
> In fact, it appears that no driver is using V4L2_CID_FOCUS_RELATIVE at the
> moment. So we could as well deprecate it (or remove from documentation
> altogether).

Atomisp and ov5693 are using it, but only to manipulate the value
behind V4L2_CID_FOCUS_ABSOLUTE. I don't know why elixir.bootlin.com
isn't picking up those references.

https://github.com/torvalds/linux/blob/master/drivers/staging/media/atomisp/pci/atomisp_ioctl.c#L1766
https://github.com/torvalds/linux/blob/master/drivers/staging/media/atomisp/i2c/ov5693/atomisp-ov5693.c#L966

  Dave