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

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Message-ID: <20190815131509.GR6133@paasikivi.fi.intel.com>
Date:   Thu, 15 Aug 2019 16:15:10 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Jacopo Mondi <jacopo@...ndi.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        "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

On Thu, Aug 15, 2019 at 04:10:53PM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Thu, Aug 15, 2019 at 04:08:49PM +0300, Sakari Ailus wrote:
> > On Thu, Aug 15, 2019 at 03:59:38PM +0300, Laurent Pinchart wrote:
> > > On Thu, Aug 15, 2019 at 10:00:25AM +0300, Sakari Ailus wrote:
> > > > On Wed, Aug 14, 2019 at 10:28:12PM +0200, Jacopo Mondi wrote:
> > > > > Add documentation for the V4L2_CID_LOCATION camera control. The newly
> > > > > added read-only control reports the camera device mounting position.
> > > > > 
> > > > > Signed-off-by: Jacopo Mondi <jacopo@...ndi.org>
> > > > > ---
> > > > >  .../media/uapi/v4l/ext-ctrls-camera.rst       | 23 +++++++++++++++++++
> > > > >  1 file changed, 23 insertions(+)
> > > > > 
> > > > > diff --git a/Documentation/media/uapi/v4l/ext-ctrls-camera.rst b/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > > > index 51c1d5c9eb00..fc0a02eee6d4 100644
> > > > > --- a/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > > > +++ b/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > > > @@ -510,6 +510,29 @@ enum v4l2_scene_mode -
> > > > >      value down. A value of zero stops the motion if one is in progress
> > > > >      and has no effect otherwise.
> > > > > 
> > > > > +``V4L2_CID_LOCATION (integer)``
> > > > > +    This read-only control describes the camera location by reporting its
> > > > > +    mounting position on the device where the camera is installed. This
> > > > > +    control is particularly meaningful for devices which have a well defined
> > > > > +    orientation, such as phones, laptops and portable devices as the camera
> > > > > +    location is expressed as a position relative to the device intended
> > > > > +    usage position. In example, a camera installed on the user-facing side
> > > > 
> > > > s/In/For/
> > > > 
> > > > > +    of a phone device is said to be installed in the ``V4L2_LOCATION_FRONT``
> > > > > +    position.
> > > > > +
> > > > > +
> > > > > +
> > > > > +.. flat-table::
> > > > > +    :header-rows:  0
> > > > > +    :stub-columns: 0
> > > > > +
> > > > > +    * - ``V4L2_LOCATION_FRONT``
> > > > > +      - The camera device is located on the front side of the device.
> > > > > +    * - ``V4L2_LOCATION_BACK``
> > > > > +      - The camera device is located on the back side of the device.
> > > > > +
> > > > > +
> > > > > +
> > > > >  .. [#f1]
> > > > >     This control may be changed to a menu control in the future, if more
> > > > >     options are required.
> > > > 
> > > > There's an effective limit of 64 for menus. ACPI has less than ten
> > > > different locations for a device, I think 64 will be enough here.
> > > > 
> > > > So I'd be actually in favour of switching to a menu.
> > > 
> > > Why ? As you explained yourself, it's a static read-only control, all it
> > > needs to report is a single value.
> > 
> > Yes. That's true. It wasn't meant for this but it's nevertheless a
> > convenient API to get that information, both as integer and string.
> 
> But why is that needed ? The integer seems enough to me.

Because it's a qualitative control, not a quantitative one.

-- 
Sakari Ailus
sakari.ailus@...ux.intel.com