linux-kernel - Re: [PATCHv2 1/3] media: v4l UAPI docs: document ROI selection targets

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Date:   Wed, 17 Mar 2021 17:08:52 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Ricardo Ribalda <ribalda@...omium.org>
Subject: Re: [PATCHv2 1/3] media: v4l UAPI docs: document ROI selection
 targets

On (21/03/17 09:04), Ricardo Ribalda Delgado wrote:
> On Wed, Mar 17, 2021 at 2:31 AM Sergey Senozhatsky
> <sergey.senozhatsky.work@...il.com> wrote:
> >
> > On (21/03/16 19:19), Ricardo Ribalda Delgado wrote:
> > > > +Configuration of Region of Interest (ROI)
> > > > +=========================================
> > > > +
> > > > +The range of coordinates of the top left corner, width and height of
> > > > +areas that can be ROI is given by the ``V4L2_SEL_TGT_ROI_BOUNDS`` target.
> > > > +It is recommended for the driver developers to put the top/left corner
> > > > +at position ``(0,0)``. The rectangle's coordinates are in global sensor
> > > > +coordinates. The units are in pixels and independent of the field of view.
> > > > +They are not impacted by any cropping or scaling that is currently being
> > > > +used.
> > >
> > > Can we also mention binning here?
> >
> > What's binning? Is it in the UVC spec?
> 
> Binning is when you reduce an image by adding up surrounding pixels.
> 
> So you have a 100x100 image that you convert to a 50x50 but showing
> the same area of interest.

I see. Hmm, not sure if I can comment on this. It's not in the spec,
so it might be up to the firmware, maybe. What do you think?

> > > > diff --git a/include/uapi/linux/v4l2-common.h b/include/uapi/linux/v4l2-common.h
> > > > index 7d21c1634b4d..d0c108fba638 100644
> > > > --- a/include/uapi/linux/v4l2-common.h
> > > > +++ b/include/uapi/linux/v4l2-common.h
> > > > @@ -78,6 +78,14 @@
> > > >  #define V4L2_SEL_TGT_COMPOSE_BOUNDS    0x0102
> > > >  /* Current composing area plus all padding pixels */
> > > >  #define V4L2_SEL_TGT_COMPOSE_PADDED    0x0103
> > > > +/* Current Region of Interest area */
> > > > +#define V4L2_SEL_TGT_ROI_CURRENT       0x0200
> > > > +/* Default Region of Interest area */
> > > > +#define V4L2_SEL_TGT_ROI_DEFAULT       0x0201
> > > > +/* Region of Interest bounds */
> > > > +#define V4L2_SEL_TGT_ROI_BOUNDS        0x0202
> > > > +/* Set Region of Interest area */
> > > > +#define V4L2_SEL_TGT_ROI               0x0203
> > >
> > > Nit: Maybe it could be a good idea to split doc and code. This way the
> > > backports/fixes are easier.
> >
> > I'm quite sure this is the first time I'm being asked to split code
> > and documentation :) I'm usually asked to do the opposite - merge code
> > and documentation.
> 
> I got answered in both directions.  I prefer to split it because the
> doc can go to different audience than the code, and then it makes my
> life easier when backporting.
> 
> But if you or Laurent prefer  otherwise I am of course happy with any option ;)

Either way works for me. Laurent, any preferences?

	-ss