linux-kernel - Re: [PATCH] drm: rcar-du: Add r8a77980 support

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Date:   Fri, 13 Sep 2019 10:57:52 +0200
From:   Simon Horman <horms@...ge.net.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVERS FOR RENESAS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: rcar-du: Add r8a77980 support

On Fri, Sep 13, 2019 at 10:30:45AM +0200, Geert Uytterhoeven wrote:
> On Fri, Sep 13, 2019 at 10:21 AM Simon Horman <horms@...ge.net.au> wrote:
> > On Thu, Sep 12, 2019 at 01:00:41PM +0300, Sergei Shtylyov wrote:
> > > On 11.09.2019 22:25, Kieran Bingham wrote:
> > > > Add direct support for the r8a77980 (V3H).
> > > > The V3H shares a common, compatible configuration with the r8a77970
> > > > (V3M) so that device info structure is reused.
> > >
> > >    Do we really need to add yet another compatible in this case?
> > > I just added r8a77970 to the compatible prop in the r8a77980 DT. That's why
> > > a patch like this one didn't get posted by me.
> >
> > The reason for having per-SoC compat strings is that the IP blocks
> > are not versioned and while we can observe that there are similarities
> > between, f.e. the DU on the r8a77970 and r8a77980, we can't be certain that
> > differences may not emerge at some point. By having per-SoC compat strings
> > we have the flexibility for the driver to address any such differences as
> > the need arises.
> 
> Thanks, that is the generic reason, applicable to all IP blocks without
> version registers.
> 
> For the Display Unit, there are documented differences (e.g. number and type
> of ports), so we definitely need it there.

Ack.

> > My recollection is that this scheme has been adopted for non-versioned
> > Renesas IP blocks since June 2015 and uses of this scheme well before that.
> >
> > > > Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> >
> > Reviewed-by: Simon Horman <horms+renesas@...ge.net.au>
> 
> 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
>