linux-kernel - Re: [PATCH v15 18/19] media: uvcvideo: implement UVC v1.5 ROI

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Message-ID: <CANiDSCvP5eVuSGMi3R4eAkY2-ou=nqrTS1dnAv0Odbcq5UHa+w@mail.gmail.com>
Date: Thu, 14 Nov 2024 21:28:24 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Gergo Koteles <soyer@....hu>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Hans de Goede <hdegoede@...hat.com>, 
	Ricardo Ribalda <ribalda@...nel.org>, Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Hans Verkuil <hverkuil@...all.nl>, Yunke Cao <yunkec@...omium.org>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Yunke Cao <yunkec@...gle.com>
Subject: Re: [PATCH v15 18/19] media: uvcvideo: implement UVC v1.5 ROI

Hi

On Thu, 14 Nov 2024 at 21:16, Gergo Koteles <soyer@....hu> wrote:
>
> Hi Ricardo,
>
> On Thu, 2024-11-14 at 21:03 +0100, Ricardo Ribalda wrote:
> > Hi Gergo
> >
> > Sorry, I forgot to reply to your comment in v14.
> >
> > On Thu, 14 Nov 2024 at 20:53, Gergo Koteles <soyer@....hu> wrote:
> > >
> > > Hi Ricardo,
> > >
> > > On Thu, 2024-11-14 at 19:10 +0000, Ricardo Ribalda wrote:
> > > >
> > > > +     },
> > > > +     {
> > > > +             .id             = V4L2_CID_UVC_REGION_OF_INTEREST_AUTO,
> > > > +             .entity         = UVC_GUID_UVC_CAMERA,
> > > > +             .selector       = UVC_CT_REGION_OF_INTEREST_CONTROL,
> > > > +             .size           = 16,
> > > > +             .offset         = 64,
> > > > +             .v4l2_type      = V4L2_CTRL_TYPE_BITMASK,
> > > > +             .data_type      = UVC_CTRL_DATA_TYPE_BITMASK,
> > > > +             .name           = "Region Of Interest Auto Controls",
> > > > +     },
> > > >  };
> > > >
> > >
> > > Wouldn't be better to use 8 V4L2_CTRL_TYPE_BOOLEAN controls for this?
> >
> > If I create 8 Booleans, they will always be shown in the device. And
> > the user will not have a way to know which values are available and
> > which are not.
> >
> > We will also fail the v4l2-compliance test, because there will be up
> > to 7 boolean controls that will not be able to be set to 1, eventhough
> > they are writable.
> >
>
> And can't it be that only those returned by GET_MAX be added?
>
> ```
> The bmAutoControls bitmask determines which, if any, on board features
> should track to the region of interest. To detect if a device supports
> a particular Auto Control, use GET_MAX which returns a mask indicating
> all supported Auto Controls.
> ```
>
> Sorry for the misunderstanding, I just don't quite understand.

I guess we could, but we would have to make a big change in the way
the controls are probed today. uvc does not use the control framework.

What will be the benefit of using 8 controls?
- Applications still have to know what those controls do, they should
not rely on the control name.
- Changing from lets say AUTO_EXPOSURE to AUTO_FOCUS, will require to
send at least 2 controls via v4l2_s_ext_control... I think it is more
practical and less prone to errrors to send just one control

If the number of autos were unknown, then having multiple controls
could be a good idea, but they are part of the uvc standard and
unlikely to be changed.


Thanks!
>
> Thanks,
>
> Gergo



-- 
Ricardo Ribalda