linux-kernel - Re: [PATCH v2 01/19] dt-bindings: display: renesas,cmm: Add R-Car CMM documentation

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Date:   Tue, 20 Aug 2019 09:53:44 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Koji Matsuoka <koji.matsuoka.xm@...esas.com>, muroya@....co.jp,
        VenkataRajesh.Kalakodima@...bosch.com,
        Harsha.ManjulaMallikarjun@...bosch.com,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/19] dt-bindings: display: renesas,cmm: Add R-Car CMM documentation

Hi Jacopo,

On Tue, Aug 20, 2019 at 9:47 AM Jacopo Mondi <jacopo@...ndi.org> wrote:
> On Mon, Aug 19, 2019 at 03:45:54PM +0200, Geert Uytterhoeven wrote:
> > On Mon, Jul 8, 2019 at 9:58 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > On Sat, Jul 6, 2019 at 4:07 PM Jacopo Mondi <jacopo+renesas@...ndi.org> wrote:
> > > > Add device tree bindings documentation for the Renesas R-Car Display
> > > > Unit Color Management Module.
> > > >
> > > > CMM is the image enhancement module available on each R-Car DU video
> > > > channel on R-Car Gen2 and Gen3 SoCs (V3H and V3M excluded).
> > > >
> > > > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > >
> > > Thanks for your patch!
> > >
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/display/renesas,cmm.txt
> > > > @@ -0,0 +1,25 @@
> > > > +* Renesas R-Car Color Management Module (CMM)
> > > > +
> > > > +Renesas R-Car image enhancement module connected to R-Car DU video channels.
> > > > +
> > > > +Required properties:
> > > > + - compatible: shall be one of:
> > > > +   - "renesas,rcar-gen3-cmm"
> > > > +   - "renesas,rcar-gen2-cmm"
> > >
> > > Why do you think you do not need SoC-specific compatible values?
> > > What if you discover a different across the R-Car Gen3 line tomorrow?
> > > Does the IP block have a version register?
> >
> > Do you have an answer to these questions?
>
> It does not seem to me that CMM has any version register, nor there
> are differences between the different Gen3 SoCs..
>
> However, even if we now define a single compatible property for
> gen3/gen2 and we later find out one of the SoC needs a soc-specific
> property we can safely add it and keep the generic gen3/gen2 one as
> fallback.. Does it work for you?

Unfortunately that won't work, as the existing DTBs won't have the
soc-specific compatible value.
You could still resort to soc_device_match(), but it is better to avoid that.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds