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

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Date:   Fri, 13 Sep 2019 12:03:59 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Simon Horman <horms@...ge.net.au>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        linux-renesas-soc@...r.kernel.org, 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

Hello,

On Fri, Sep 13, 2019 at 10:21:29AM +0200, Simon Horman 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.
> 
> 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.

Sure, but we could use

	compatible = "renesas,du-r8a77980", "renesas,du-r8a77970";

in DT without updating the driver. If the r8a77980 turns out to be
different, we'll then update the driver without a need to modify DT. I'm
fine either way, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> > > Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> 
> Reviewed-by: Simon Horman <horms+renesas@...ge.net.au>

-- 
Regards,

Laurent Pinchart