Re: [PATCH 3/3] memory: renesas-rpc-if: Add support for RZ/T2H SoC

[Geert Uytterhoeven]

Hi Krzysztof,

On Mon, 16 Mar 2026 at 15:46, Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
> On 16/03/2026 15:34, Geert Uytterhoeven wrote:
> > On Mon, 16 Mar 2026 at 15:21, Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
> >> On 16/03/2026 15:16, Wolfram Sang wrote:
> >>>> Add a new compatible string "renesas,r9a09g077-xspi" for RZ/T2H while
> >>>> reusing the existing xspi_info_r9a09g047 OF data. This allows the driver
> >>>> to bind correctly on RZ/T2H while the register differences can be handled
> >>>> in future updates as the affected configuration registers are not currently
> >>>> accessed by the driver.
> >>>
> >>> This sounds fragile to me. Can you add a comment somewhere in the driver
> >>> or headers so people wanting to use these registers will find out that
> >>> the SoCs are not compatible anymore?
> >>
> >> IMO, this patch is not needed. If you need to handle differences in
> >> registers, then you add dedicated OF data.
> >>
> >> The change here (with the bindings) is actually confusing, because
> >> effectively it says two contradictory statements:
> >> 1. Driver patch: devices are different but they are compatible in
> >> meaning of DT,
> >> 2. Bindings: devices are not compatible
> >>
> >> So you need to decide which above, but not both.
> >>
> >> Eventually provide extensive arguments in terms of how DT understands
> >> compatibility.
> >
> > I disagree.  Using the same of_data can does not mean the devices are
> > 100% compatible.  It can also mean that the devices are different, but
>
> I did not say 100% compatible. I said compatible.

Fair enough.

> >   a) The differences are not handled yet, because the extra features of
> >      one variant (or both variants)  are not yet supported by the supported by the driver
> So that's why I mentioned how DT understands compatibility. Above does
> not matter, sorry.
>
> Extra features means subset/superset.

I haven't looked at the differences between the two variants here,
but I doubt one of them is a superset of the other. Probably both are
supersets of a common subvariant that doesn't really exist ;-)

> >   b) The differences are not handled explicitly, but implicitly,
> >      or elsewhere.
> >      E.g. the different number of resets is handled implicitly through
> >      devm_reset_control_array_get_exclusive().
>
> Still not an argument in meaning of DT compatibility. Implementation
> uses the same ABI (through devm_reset_control_array_get_exclusive),
> right? So devices are compatible for Linux kernel.

Linux is not the only user of DT.

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