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

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Message-ID: <20250530-squatting-chatroom-230f035f18ef@spud>
Date: Fri, 30 May 2025 17:41:16 +0100
From: Conor Dooley <conor@...nel.org>
To: Anup Patel <apatel@...tanamicro.com>
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 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.

Otherwise, the bindings are all:
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Cheers,
Conor.

> +
> +required:
> +  - compatible
> +  - mboxes
> +  - "#clock-cells"
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    clock-controller {
> +        compatible = "riscv,rpmi-clock";
> +        mboxes = <&mpxy_mbox 0x1000 0x0>;
> +        #clock-cells = <1>;
> +    };
> +...
> -- 
> 2.43.0
> 

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