Re: [PATCH/RFC 00/14] R-Car X5H Ironhide SCMI CPG/MDLC remapping

Geert Uytterhoeven
2026-04-24T11:28:24Z

Hi Kevin,

On Thu, 23 Apr 2026 at 00:48, Kevin Hilman <khilman@baylibre.com> wrote:
> Geert Uytterhoeven <geert+renesas@glider.be> writes:
> > TL;DR:
> >
> > Describe hardware in DT, and perform the mapping to SCMI in Linux.
> >
> > The Renesas R-Car X5H-based Ironhide board is the first Renesas
> > SoC/board combination that implements the ARM System Control and
> > Management Interface (SCMI).
> >
> > This means Linux can no longer perform various system operations (e.g.
> > clock, power domain, and reset control) by accessing the hardware
> > directly. Instead, these operations are abstracted according to various
> > SCMI sub-protocols, and Linux has to send messages to an SCMI-compliant
> > firmware running on a System Control Processor (SCP).
> > More specifically, the R-Car X5H SCP FW SCMI controls access to:
> > 1. Core clocks and module clocks,
> > 2. Module resets,
> > 3. Power domains,
>
> I'm very curious how power domain hierarchy is described on this SoC,
> because one more issue to add to your list is that hierarchy cannot be
> described for power domains in SCMI.

So far I had no need for such a description. AFAIK, this is handled
inside the SCMI firmware, which does know the hierarchy. Hence the
firmware can power up a domain when any of its children is powered up,
and power it down when the last of its children is powered down?

I think the clue lies in having a PSCI top-level domain, cfr. what
you wrote in [1]:

"But... how do I describe the relationship of this hierarchy? In
particular, when the SCMI-controlled PDs are actually subdomains of a
top-level, non-SCMI PD."

Or am I missing something?

So far I have used only a few devices on R-Car X5H, and e.g. the
serial ports are in the always-on domain. I did experiment with
a dummy UFS driver, as UFS is inside a real power domain, and that
seemed to work fine.

[1] https://lore.kernel.org/arm-scmi/7hecy3h7ky.fsf@baylibre.com/

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