linux-kernel - Re: [PATCH v4 09/23] dt-bindings: clock: Add RPMI clock service controller bindings

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Message-ID: <CAK9=C2X1svSheL8KFF40vXT9Fc2a5_zyX4PzWRkcR44rd3KmBw@mail.gmail.com>
Date: Tue, 10 Jun 2025 10:50:34 +0530
From: Anup Patel <apatel@...tanamicro.com>
To: Conor Dooley <conor@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jassi Brar <jassisinghbrar@...il.com>, Thomas Gleixner <tglx@...utronix.de>, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Uwe Kleine-König <ukleinek@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Len Brown <lenb@...nel.org>, Sunil V L <sunilvl@...tanamicro.com>, 
	Rahul Pathak <rpathak@...tanamicro.com>, Leyfoon Tan <leyfoon.tan@...rfivetech.com>, 
	Atish Patra <atish.patra@...ux.dev>, Andrew Jones <ajones@...tanamicro.com>, 
	Samuel Holland <samuel.holland@...ive.com>, Anup Patel <anup@...infault.org>, 
	linux-clk@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 09/23] dt-bindings: clock: Add RPMI clock service
 controller bindings

On Fri, May 30, 2025 at 10:11 PM Conor Dooley <conor@...nel.org> wrote:
>
> On Sun, May 25, 2025 at 02:16:56PM +0530, Anup Patel wrote:
> > Add device tree bindings for the RPMI clock service group based
> > controller for the supervisor software.
> >
> > The RPMI clock service group is defined by the RISC-V platform
> > management interface (RPMI) specification.
> >
> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > ---
> >  .../bindings/clock/riscv,rpmi-clock.yaml      | 61 +++++++++++++++++++
> >  1 file changed, 61 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/clock/riscv,rpmi-clock.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/clock/riscv,rpmi-clock.yaml b/Documentation/devicetree/bindings/clock/riscv,rpmi-clock.yaml
> > new file mode 100644
> > index 000000000000..9c672a38595a
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/riscv,rpmi-clock.yaml
> > @@ -0,0 +1,61 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/clock/riscv,rpmi-clock.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V RPMI clock service group based clock controller
> > +
> > +maintainers:
> > +  - Anup Patel <anup@...infault.org>
> > +
> > +description: |
> > +  The RISC-V Platform Management Interface (RPMI) [1] defines a
> > +  messaging protocol which is modular and extensible. The supervisor
> > +  software can send/receive RPMI messages via SBI MPXY extension [2]
> > +  or some dedicated supervisor-mode RPMI transport.
> > +
> > +  The RPMI specification [1] defines clock service group for accessing
> > +  system clocks managed by a platform microcontroller. The supervisor
> > +  software can access RPMI clock service group via SBI MPXY channel or
> > +  some dedicated supervisor-mode RPMI transport.
> > +
> > +  ===========================================
> > +  References
> > +  ===========================================
> > +
> > +  [1] RISC-V Platform Management Interface (RPMI)
> > +      https://github.com/riscv-non-isa/riscv-rpmi/releases
> > +
> > +  [2] RISC-V Supervisor Binary Interface (SBI)
> > +      https://github.com/riscv-non-isa/riscv-sbi-doc/releases
> > +
> > +properties:
> > +  compatible:
> > +    description:
> > +      Intended for use by the supervisor software.
> > +    const: riscv,rpmi-clock
> > +
> > +  mboxes:
> > +    maxItems: 1
> > +    description:
> > +      Mailbox channel of the underlying RPMI transport or SBI message proxy channel.
> > +
> > +  "#clock-cells":
> > +    const: 1
>
> Could you please add some description here as to what this clock-cell
> actually does? On a normal clock controller someone might cite an
> include file with a huge list of defines for what numbers map to what
> clock. In this case, this value is CLOCK_ID in the spec, so it's
> completely platform specific as to what they mean so citing some include
> isn't helpful, so just mention that it is CLOCK_ID and the meanings are
> platform specific.
>
> I suppose technically it can be something other than CLOCK_ID, if this is
> used when the SBI message proxy extension is provided by an SBI
> implementation that uses a non-RPMI transport, but I don't think that's a
> can of worms worth bringing up in the binding. Anyone doing that can put
> 2+2 together I think.

The #clock-cell value must be the platform specific CLOCK_ID as defined by
the RISC-V Platform Management Interface (RPMI) specification irrespective
of the underlying mechanism (e.g. SBI MPXY or RPMI transport) used to
access the RPMI Clock service group.

Each platform must publish their CLOCK_ID values as part of their SoC docs
or as a header used by their SoC DTS files.

I will add "description:" for clock-cells along these lines.

Regards,
Anup