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

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Message-ID: <YFFb2ePwiW+8ti4D@google.com>
Date:   Wed, 17 Mar 2021 10:31:05 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     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>
Subject: Re: [PATCHv2 1/3] media: v4l UAPI docs: document ROI selection
 targets

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?

> > +The top left corner, width and height of the Region of Interest area
> > +currently being employed by the device is given by the
> > +``V4L2_SEL_TGT_ROI_CURRENT`` target. It uses the same coordinate system
> > +as ``V4L2_SEL_TGT_ROI_BOUNDS``.
> 
> Why do we need current? Cant we just read back V4L2_SEL_TGT_ROI ?

We don't. Will remove it.

> > +    * - ``V4L2_SEL_TGT_ROI_CURRENT``
> > +      - 0x0200
> > +      - Current Region of Interest rectangle.
> > +      - Yes
> > +      - No
> > +    * - ``V4L2_SEL_TGT_ROI_DEFAULT``
> > +      - 0x0201
> > +      - Suggested Region of Interest rectangle.
> > +      - Yes
> > +      - No
> > +    * - ``V4L2_SEL_TGT_ROI_BOUNDS``
> > +      - 0x0202
> > +      - Bounds of the Region of Interest rectangle. All valid ROI rectangles fit
> > +       inside the ROI bounds rectangle.
> > +      - Yes
> > +      - No
> > +    * - ``V4L2_SEL_TGT_ROI``
> > +      - 0x0203
> > +      - Sets the new Region of Interest rectangle.
> > +      - Yes
> > +      - No
> As mentioned before I think we should not have TGT_ROI_CURRENT and TGT_ROI

Agreed.

> > 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.