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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Kieran, Laurent,

On Mon, Dec 16, 2019 at 10:47 AM Kieran Bingham
<kieran.bingham+renesas@ideasonboard.com> wrote:
> On 13/12/2019 00:48, Laurent Pinchart wrote:
> > On Mon, Dec 09, 2019 at 12:41:07PM +0000, Kieran Bingham wrote:
> >> On 13/09/2019 10:03, Laurent Pinchart wrote:
> >>> 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";
>
> We already do in arch/arm64/boot/dts/renesas/r8a77980.dtsi.
>
> However that is the *only* non r8a77980 reference in the file so it,
> itself looks *very* much out of place.
>
>
> Furthermore, the main purpose of this patch is that we clearly document
> the driver as supporting the r8a77980 in the bindings (No mention that
> you must use the ..970 binding), yet in actual fact - the driver could
> not currently support loading a device with the following compatible:
>
>         compatible = "renesas,du-r8a77980";
>
>
> >>> 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@ideasonboard.com>
> >>
> >> Thanks,
> >>
> >> This patch has an RB tag from you, and Simon, but alas I don't believe
> >> it has been picked up in your drm/du/next branch.
> >>
> >> Is this patch acceptable? Or do I need to repost?
> >
> > Could you just confirm I should apply this patch, and not go for the
> > alternative proposal above ?
>
> I believe the alternative proposal above is what we have today isn't it?
>
>
> Yes, I do believe we should apply this patch.

+1.

I'm waiting for the driver part to go upstream, so I can apply the DTS patch.
Note that this will lead to a messy situation in LTS, as the DTS patch will
likely be backported, so the driver part must be backported, too.

> I'm going to assume you haven't read the other arguments on this thread
> so I'll paste them here:

Thanks for recollecting! ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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