linux-kernel - Re: [PATCH 1/2] dt-bindings: media: renesas,vin: Document renesas-vin-ycbcr-8b-g property

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Message-ID: <20200725081146.GF2729799@oden.dyn.berto.se>
Date:   Sat, 25 Jul 2020 10:11:46 +0200
From:   Niklas <niklas.soderlund@...natech.se>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH 1/2] dt-bindings: media: renesas,vin: Document
 renesas-vin-ycbcr-8b-g property

Hi Lad,

On 2020-07-24 22:11:31 +0100, Lad, Prabhakar wrote:
> Hi Niklas,
> 
> Thank you for the review.
> 
> On Fri, Jul 24, 2020 at 8:37 PM Niklas <niklas.soderlund@...natech.se> wrote:
> >
> > Hi Lad,
> >
> > Thanks for your patch.
> >
> > On 2020-07-24 15:58:51 +0100, Lad Prabhakar wrote:
> > > Add a DT property "renesas-vin-ycbcr-8b-g" to select YCbCr422 8-bit data
> > > input pins.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > Reviewed-by: Biju Das <biju.das.jz@...renesas.com>
> > > ---
> > >  Documentation/devicetree/bindings/media/renesas,vin.yaml | 13 +++++++++++++
> > >  1 file changed, 13 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/media/renesas,vin.yaml b/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > index 53c0a72..7dfb781 100644
> > > --- a/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > +++ b/Documentation/devicetree/bindings/media/renesas,vin.yaml
> > > @@ -106,6 +106,12 @@ properties:
> > >
> > >            remote-endpoint: true
> > >
> > > +          renesas-vin-ycbcr-8b-g:
> >
> > I think the preferred format for vendor specific properties are
> > "<vendor>,<property>".
> >
> Indeed and I had it as renesas,vin-ycbcr-8b-g but dt_bindings_check
> complained about it.

I see, what was the error?

> 
> > This nit apart I'm not sure a property is the right way here. Could it
> > not be possible on some designs to have two different sensors one wired
> > to DATA[7:0] and the other to DATA[15:8] and by controlling the
> > VNDRM2_YDS register at runtime switch between the two? If so adding a DT
> > property to hard-code one of the two options would prevent this. I fear
> > we need to think of a runtime way to deal with this.
> >
> Aha Gen2 and Gen3 hardware manuals have a bit different description
> about the YDS field. (I was working R8a7742 SoC so I referred Gen2
> manual)

Ahh, I think we should use the Gen3 names as I find them overall an 
improvement over the Gen2 ones.

> 
> > The best way to do that I think is to extend the port@0 node to allow
> > for two endpoints, one for each of the two possible parallel sensors.
> > This would then have to be expressed in the media graph and selection if
> > YDS should be set or not depend on which media links are enabled.
> >
> In that case how do we handle endpoint matching each would have two
> subdevs to be matched.

It would be handle in the same was as the multiple endpoints in port@1.

> And in case non media-ctl cases we cannot
> switch between subdevs.

For the Gen2 none media graph enabled mode this could be handled with 
the S_INPUT ioctl. For this feature to be merged however I it needs to 
be possible to select input both in Gen2 and Gen3 I'm afraid. I'm hoping 
to one day breakout the non MC part of this driver into a new one and 
mark it as deprecated and switch to the MC code paths for Gen2.

> 
> Cheers,
> --Prabhakar
> 
> > > +            type: boolean
> > > +            description:
> > > +              If present this property specifies to selects VIN_G[7:0] as data pins for YCbCr422 8-bit data.
> > > +            default: false
> > > +
> > >          required:
> > >            - remote-endpoint
> > >
> > > @@ -168,6 +174,13 @@ properties:
> > >
> > >                remote-endpoint: true
> > >
> > > +              renesas-vin-ycbcr-8b-g:
> > > +                type: boolean
> > > +                description:
> > > +                  If present this property specifies to selects VIN_G[7:0] as data pins for
> > > +                  YCbCr422 8-bit data.
> > > +                default: false
> > > +
> > >              required:
> > >                - remote-endpoint
> > >
> > > --
> > > 2.7.4
> > >
> >
> > --
> > Regards,
> > Niklas Söderlund

-- 
Regards,
Niklas Söderlund