linux-kernel - Re: [RFC 2/5] media: v4l2-ctrl: Document V4L2_CID

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Message-ID: <20190902085303.GG4777@pendragon.ideasonboard.com>
Date:   Mon, 2 Sep 2019 11:53:03 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
        <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/5] media: v4l2-ctrl: Document V4L2_CID_LOCATION

Hi Pawel,

On Mon, Sep 02, 2019 at 10:27:39AM +0200, Pavel Machek wrote:
> On Mon 2019-09-02 11:19:42, Laurent Pinchart wrote:
> > On Mon, Sep 02, 2019 at 10:06:57AM +0200, Pavel Machek wrote:
> >>>>> Single integer. It's read-only, so it just reports the location.
> >>>>> 
> >>>>> It would be different if this was a writable control: then you need to
> >>>>> know which locations are possible to set, and that requires a menu type.
> >>>>> 
> >>>>> But it doesn't make sense to set the location from software. However, the
> >>>>> location might change as a result of other changes: e.g. if the camera
> >>>>> has motor control of the tilt and the tilt changes from forward facing to
> >>>>> downward facing, then the driver might change the location from FRONT
> >>>>> to DOWN. A convoluted example perhaps, but this is just brainstorming.
> >>>> 
> >>>> There are phones with exactly such camera setup. And yes, it makes
> >>>> sense to be writable in that case, as software can move the camera in
> >>>> such case.
> >>> 
> >>> Out of curiosity, what phones are those ?
> >> 
> >> This one:
> >> 
> >> https://www.samsung.com/global/galaxy/galaxy-a80/
> > 
> > Interesting device. I'm not sure we should control that through a
> > location control though, as it seems there's more than the rotation of
> > the camera involved. In any case I wouldn't care about it for now, and
> > turn the location control from read-only to read-write later if needed.
> > We need more information and more thought to support that use case.
> 
> Well, the mechanism is there just to rotate the camera.

But we don't know how it's implemented, it could be heavily
firmware-based for instance.

> Anyway, that phone is probably nowhere close to having mainline
> support, so...

If we need to support such a device in the future (and I hope we will
:-)) then I'm totally fine expanding the features of the location
control. My only concern is that I don't want to over-design it right
now without having enough information about the hardware that would make
use of it.

-- 
Regards,

Laurent Pinchart