Re: [PATCH 1/4] dt-bindings: i2c: rcar: Add r8a77470 support

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On Mon, Sep 24, 2018 at 09:10:53AM +0000, Fabrizio Castro wrote:
> Hello Simon,
> 
> Thank you for the feedback.
> 
> > Subject: Re: [PATCH 1/4] dt-bindings: i2c: rcar: Add r8a77470 support
> >
> > On Fri, Sep 21, 2018 at 06:36:58PM +0100, Fabrizio Castro wrote:
> > > Although the I2C IP found in the RZ/G1C is not exactly the same
> > > as the one found in the R-Car Gen2 family or R-Car Gen3 family,
> > > it can still be considered as compatible with R-Car Gen2 from
> > > a software perpective.
> > > This patch therefore documents the SoC specific compatible string,
> > > and the compatibility with Gen2 fallback is retained.
> > >
> > > Signed-off-by: Fabrizio Castro <fabrizio.castro@xxxxxxxxxxxxxx>
> > > Reviewed-by: Biju Das <biju.das@xxxxxxxxxxxxxx>
> > > ---
> > >  Documentation/devicetree/bindings/i2c/i2c-rcar.txt | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/i2c/i2c-rcar.txt b/Documentation/devicetree/bindings/i2c/i2c-rcar.txt
> > > index 39cd21d..671e2a1 100644
> > > --- a/Documentation/devicetree/bindings/i2c/i2c-rcar.txt
> > > +++ b/Documentation/devicetree/bindings/i2c/i2c-rcar.txt
> > > @@ -4,6 +4,7 @@ Required properties:
> > >  - compatible:
> > >  "renesas,i2c-r8a7743" if the device is a part of a R8A7743 SoC.
> > >  "renesas,i2c-r8a7745" if the device is a part of a R8A7745 SoC.
> > > +"renesas,i2c-r8a77470" if the device is a part of a R8A77470 SoC.
> >
> > It seems to me that the RZ/G1C has some extra registers described for
> > I2C when compared with both other RZ/G1 and R-Car Gen2 SoCs.
> 
> Exactly. The extra registers found with the RZ/G1C I2C controller are also found in R-Car Gen3,
> but the driver doesn't handle them. R-Car Gen3 has more registers on top of those found
> with the RZ/G1C.
> 
> >
> > Am I correct in assuming that operation is correct for the RZ/G1C
> > when using the fallback compat string for RZ/G1 and R-Car Gen2 SoCs?
> 
> Since the driver is not using ICCCR2, ICMPR, ICHPR, and ICLPR, what's left is compatible
> with R-Car Gen2.
> I have tested I2C4 on its own and with the HDMI transmitter found on the iwg23s, and
> so far so good.
> 
> >
> > And that, speculating wildly, in future it may be possible for
> > the driver to use these extra resgisters, f.e. by via a match on
> > the renesas,i2c-r8a77470 compat string?
> 
> Exactly. If anybody ever looks into supporting the missing functionality the SoC
> specific string could be used to pick up better driver support (although Gen2
> support would probably still be alright).
> 
> I hope this clarifies things a little bit better.

Thanks, it helps a lot.



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