linux-kernel - Re: [PATCH v8 08/24] dt-bindings: clock: Add RPMI clock service message proxy bindings

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Message-ID: <CAK9=C2WRVHZ4FdoW0fKRRFg6qAC5asn03dHj_NXkMKfBXKkXdA@mail.gmail.com>
Date: Mon, 28 Jul 2025 14:49:23 +0530
From: Anup Patel <apatel@...tanamicro.com>
To: Stephen Boyd <sboyd@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Conor Dooley <conor+dt@...nel.org>, Jassi Brar <jassisinghbrar@...il.com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Linus Walleij <linus.walleij@...aro.org>, 
	Michael Turquette <mturquette@...libre.com>, Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Rob Herring <robh@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Uwe Kleine-König <ukleinek@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Alexandre Ghiti <alex@...ti.fr>, 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-acp <i@...r.kernel.org>, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH v8 08/24] dt-bindings: clock: Add RPMI clock service
 message proxy bindings

On Sun, Jul 27, 2025 at 11:53 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Anup Patel (2025-07-25 09:16:12)
> > On Fri, Jul 25, 2025 at 8:12 AM Stephen Boyd <sboyd@...nel.org> wrote:
> > >
> > > Quoting Anup Patel (2025-07-04 00:03:40)
> > > > Add device tree bindings for the RPMI clock service group based
> > > > message proxy implemented by the SBI implementation (machine mode
> > > > firmware or hypervisor).
> > > >
> > > > The RPMI clock service group is defined by the RISC-V platform
> > > > management interface (RPMI) specification.
> > > >
> > > > Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> > > > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > > [...]
> > > > +additionalProperties: false
> > > > +
> > > > +examples:
> > > > +  - |
> > > > +    clock-controller {
> > >
> > > Maybe the name should be 'clock-service' then? I don't understand SBI so
> > > not sure why this is in DT to begin with. Is something consuming this
> > > node? Or a driver is binding to it?
> >
> > SBI is a syscall style interface between SBI implementation (aka
> > M-mode firmware or hypervisor) and supervisor software (aka
> > Linux kernel).
> >
> > We have DT based drivers in OpenSBI (M-mode firmware). This
> > binding allows Clock message proxy driver to be probed on the
> > OpenSBI side. The clock message proxy driver allows Linux
> > RPMI clock driver to send RPMI messages via OpenSBI as
> > proxy thereby sharing the RPMI transport between OpenSBI
> > and Linux kernel.
>
> Let me try to clarify my confusion. A 'clock-controller' node without a
> '#clock-cells' property is confusing.

Ahh, I see your point. The node name need not be 'clock-controller'
since the node is for a firmware driver which provides MPXY channel
to supervisor software (aka Linux kernel).

>
> It's not providing clks? The SBI firmware is not discoverable? Do you
> have a pointer to the DTS for this node and the clock controller node in
> the next patch? I'd like to understand why this is named a clock
> controller when it doesn't provide clks.

The firmware driver is not providing clks. Also, the SBI firmware and
various SBI extensions are indeed discoverable from supervisor software.

On the Linux side, we have two DT nodes:
1) One DT node for the SBI MPXY based mailbox-controller
    (Refer, https://lore.kernel.org/all/20250704070356.1683992-3-apatel@ventanamicro.com/)
2) Second DT node for the clock-controller based on the
    RPMI clock service group.
    (Refer, https://lore.kernel.org/all/20250704070356.1683992-10-apatel@ventanamicro.com/)

Regards,
Anup