linux-kernel - Re: [PATCH v9 02/24] dt-bindings: mailbox: Add bindings for RISC-V SBI MPXY extension

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Message-ID: <612a13d3-d3a6-460b-90fd-c26e47b80711@sifive.com>
Date: Fri, 1 Aug 2025 23:12:28 -0500
From: Samuel Holland <samuel.holland@...ive.com>
To: Anup Patel <apatel@...tanamicro.com>
Cc: 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>,
 Anup Patel <anup@...infault.org>, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Conor Dooley <conor.dooley@...rochip.com>,
 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>
Subject: Re: [PATCH v9 02/24] dt-bindings: mailbox: Add bindings for RISC-V
 SBI MPXY extension

Hi Anup,

On 2025-07-28 4:40 AM, Anup Patel wrote:
> Add device tree bindings for the RISC-V SBI Message Proxy (MPXY)
> extension as a mailbox controller.
> 
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>  .../bindings/mailbox/riscv,sbi-mpxy-mbox.yaml | 51 +++++++++++++++++++
>  1 file changed, 51 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/riscv,sbi-mpxy-mbox.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mailbox/riscv,sbi-mpxy-mbox.yaml b/Documentation/devicetree/bindings/mailbox/riscv,sbi-mpxy-mbox.yaml
> new file mode 100644
> index 000000000000..061437a0b45a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mailbox/riscv,sbi-mpxy-mbox.yaml
> @@ -0,0 +1,51 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mailbox/riscv,sbi-mpxy-mbox.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: RISC-V SBI Message Proxy (MPXY) extension based mailbox
> +
> +maintainers:
> +  - Anup Patel <anup@...infault.org>
> +
> +description: |
> +  The RISC-V SBI Message Proxy (MPXY) extension [1] allows supervisor
> +  software to send messages through the SBI implementation (M-mode
> +  firmware or HS-mode hypervisor). The underlying message protocol
> +  and message format used by the supervisor software could be some
> +  other standard protocol compatible with the SBI MPXY extension
> +  (such as RISC-V Platform Management Interface (RPMI) [2]).
> +
> +  ===========================================
> +  References
> +  ===========================================
> +
> +  [1] RISC-V Supervisor Binary Interface (SBI) v3.0 (or higher)
> +      https://github.com/riscv-non-isa/riscv-sbi-doc/releases
> +
> +  [2] RISC-V Platform Management Interface (RPMI) v1.0 (or higher)
> +      https://github.com/riscv-non-isa/riscv-rpmi/releases
> +
> +properties:
> +  compatible:
> +    const: riscv,sbi-mpxy-mbox
> +
> +  "#mbox-cells":
> +    const: 2
> +    description:
> +      The first cell specifies channel_id of the SBI MPXY channel,
> +      the second cell specifies MSG_PROT_ID of the SBI MPXY channel

What is the purpose of the second mailbox cell?

The client can probe the message protocol using a SBI call, if it doesn't just
assume a protocol based on the kind of node that references this mailbox. The
SBI implementation knows the message protocol from the kind of node that
instantiates the channel (for example riscv,rpmi-mpxy-clock has
riscv,sbi-mpxy-channel-id). So this cell looks redundant.

Regards,
Samuel

> +
> +required:
> +  - compatible
> +  - "#mbox-cells"
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    mailbox {
> +          compatible = "riscv,sbi-mpxy-mbox";
> +          #mbox-cells = <2>;
> +    };