Hi Simon,
On Tue, Sep 25, 2018 at 9:47 AM Simon Horman <horms@xxxxxxxxxxxx> wrote:
> On Tue, Sep 25, 2018 at 08:47:38AM +0200, Geert Uytterhoeven wrote:
> > On Mon, Sep 24, 2018 at 8:34 PM Fabrizio Castro
> > <fabrizio.castro@xxxxxxxxxxxxxx> wrote:
> > > > Subject: Re: [PATCH 1/4] dt-bindings: mmc: renesas_sdhi: Add r8a77470 support
> > > > On Fri, Sep 21, 2018 at 1:55 PM Fabrizio Castro
> > > > <fabrizio.castro@xxxxxxxxxxxxxx> wrote:
> > > > > Document SDHI support for the RZ/G1C (a.k.a. R8A77470) SoC.
> > > > >
> > > > > Signed-off-by: Fabrizio Castro <fabrizio.castro@xxxxxxxxxxxxxx>
> > > > > Reviewed-by: Biju Das <biju.das@xxxxxxxxxxxxxx>
> >
> > > > > --- a/Documentation/devicetree/bindings/mmc/tmio_mmc.txt
> > > > > +++ b/Documentation/devicetree/bindings/mmc/tmio_mmc.txt
> > > > > @@ -17,6 +17,7 @@ Required properties:
> > > > > "renesas,sdhi-r8a7740" - SDHI IP on R8A7740 SoC
> > > > > "renesas,sdhi-r8a7743" - SDHI IP on R8A7743 SoC
> > > > > "renesas,sdhi-r8a7745" - SDHI IP on R8A7745 SoC
> > > > > + "renesas,sdhi-r8a77470" - SDHI IP on R8A77470 SoC
> > > > > "renesas,sdhi-r8a7778" - SDHI IP on R8A7778 SoC
> > > > > "renesas,sdhi-r8a7779" - SDHI IP on R8A7779 SoC
> > > > > "renesas,sdhi-r8a7790" - SDHI IP on R8A7790 SoC
> > > >
> > > > It seems RZ/G1C has two slighty different types of SD card interfaces:
> > > > 1. SDHI0 and SDHI2 use SYS-DMAC,
> > > > 2. SDHI1 can also be used as an MMC interface, and has an internal DMAC.
> > > >
> > > > Do we need to distinguish between them using the compatible value, or
> > > > are there other ways?
> > >
> > > The most sensible thing to do here is probably to distinguish between them using
> > > the compatible value, we were thinking about using the following for SDHI1:
> > > compatible = "renesas,sdhi-mmc-r8a77470", "renesas,rcar-gen3-sdhi";
> > >
> > > What do you guys think?
> >
> > Oh, so it's identical (or "sufficiently compatible") with the SD card
> > interface on R-Car Gen3?
> > "renesas,sdhi-mmc-r8a77470" may be a good way to distinguish.
> > I'm a bit reluctant to add "renesas,rcar-gen3-sdhi", though.
>
> I am also reluctant to add "renesas,rcar-gen3-sdhi", because as we are
> seeing things are not so simple wrt to compatible.
>
> Can I clarify the proposal regarding "renesas,sdhi-mmc-r8a77470",
> would it be as well as or instead of "renesas,sdhi-r8a77470" ?
AFAIU, "renesas,sdhi-r8a77470" would be still used for SDHI0 and SDHI2.
> And what is signified by "mmc" that is not implied by (some of the)
> existing compat strings?
"SDHI1 can also be used as an MMC interface".
Note that this (can also be used as an MMC interface) seems to be true
for the SD card interfaces in R-Car Gen3, too.
> Perhaps stating the obvious: this feels a lot like the problem we thought
> we had with different Gen-3 SoCs/ES versions. And in that case we decided
> against using compat strings to differentiate. The main difference here
> seems to be that we need to differentiate between different ports on the
> same SoC.
So either
a) SDHI0/2 vs. SDHI1 are different, deserving different compatible values, or
b) SDHI0/1/2 are identical, but SDHI1 is wired different, deserving the same
compatible value, but one or more additional properties describing the
different wiring.
Wolfram's proposal for b) was looking at the (lack of) dmas properties, but
that's not sufficient, as they are optional anyway.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
