Re: [PATCH 0/4] soc: renesas: Identify SoC and register with the SoC bus

[Arnd Bergmann]

On Wednesday, October 19, 2016 10:10:38 AM CEST Geert Uytterhoeven wrote:
> Hi Arnd,
> 
> On Mon, Oct 10, 2016 at 4:28 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > On Tuesday, October 4, 2016 11:09:23 AM CEST Geert Uytterhoeven wrote:
> >> Some Renesas SoCs may exist in different revisions, providing slightly
> >> different functionalities (e.g. R-Car H3 ES1.x and ES2.0). This needs to
> >> be catered for by drivers and/or platform code.  The recently proposed
> >> soc_device_match() API seems like a good fit to handle this.
> >>
> >> This patch series implements the core infrastructure to provide SoC and
> >> revision information through the SoC bus for Renesas ARM SoCs. It
> >> consists of 4 patches:
> >>   - Patch 1 avoids a crash when SoC revision information is needed and
> >>     provided early,
> >>   - Patch 2 (from Arnd) introduces the soc_device_match() API.
> >>     I don't know if, when, and through which channel this patch is
> >>     planned to go upstream,
> >>   - Patch 3 fixes a bug in soc_device_match(), causing a crash when
> >>     trying to match on an SoC attribute that is not provided (seen on
> >>     EMEV2, RZ/A, and R-Car M1A, which lack revision information),
> >>   - Patch 4 identifies Renesas SoCs and registers them with the SoC bus.
> >>
> >> Tested on (family, machine, soc_id, optional revision):
> >>
> >>     Emma Mobile EV2, EMEV2 KZM9D Board, emev2
> >>     RZ/A, Genmai, r7s72100
> >>     R-Mobile, APE6EVM, r8a73a4, ES1.0
> >>     R-Mobile, armadillo 800 eva, r8a7740, ES2.0
> >>     R-Car Gen1, bockw, r8a7778
> >>     R-Car Gen1, marzen, r8a7779, ES1.0
> >>     R-Car Gen2, Lager, r8a7790, ES1.0
> >>     R-Car Gen2, Koelsch, r8a7791, ES1.0
> >>     R-Car Gen2, Gose, r8a7793, ES1.0
> >>     R-Car Gen2, Alt, r8a7794, ES1.0
> >>     R-Car Gen3, Renesas Salvator-X board based on r8a7795, r8a7795, ES1.0
> >>     R-Car Gen3, Renesas Salvator-X board based on r8a7796, r8a7796, ES1.0
> >>     SH-Mobile, KZM-A9-GT, sh73a0, ES2.0
> >
> > As mentioned in the comment for the driver patch, I think this makes
> > a lot of sense for the machines that have a revision register, in
> > particular when the interpretation of that register is always done
> > the same way, but I'm a bit skeptical about doing it in the same driver
> > for machines that don't have the register.
> >
> > Matching by a device rather than the SoC platform also has the advantage
> > that there is no need to maintain a list of compatible numbers in the
> > driver.
> 
> Currently we (usually) use:
>   - SoC-specific compatible values, to handle known differences within the
>     same family now, and handle future unknown differences,
>   - Family-specific compatible values, which we define ourselves.
> 
> Usually drivers match on the latter.
> 
> Every time a new SoC is introduced, we have to update lots of DT binding
> docs, to add the new SoC-specific compatible values.
>
> Two-phase matching (driver code matches against "renesas,<foo>",
> driver matches against SoC using soc_device_match()) would allow to
> remove the burden of updating DT documentation all the time.
> The drivers would need updates, though.
> Another advantage would be that we can reuse .dtsi snippets for SoCs in
> the same family, which we currently can't easily do due to the SoC-specific
> compatible values.

Interesting idea, but unrelated to my comment above, which was about
the soc driver in particular, rather the drivers using it.

	Arnd