Re: [RFC PATCH v2 02/17] dt-bindings: mailbox: Add bindings for RPMI shared memory transport

[Rob Herring <robh@kernel.org>]

On Mon, Feb 03, 2025 at 02:18:51PM +0530, Anup Patel wrote:
> Add device tree bindings for the common RISC-V Platform Management
> Interface (RPMI) shared memory transport as a mailbox controller.
> 
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> ---
>  .../mailbox/riscv,rpmi-shmem-mbox.yaml        | 150 ++++++++++++++++++
>  1 file changed, 150 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/riscv,rpmi-shmem-mbox.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mailbox/riscv,rpmi-shmem-mbox.yaml b/Documentation/devicetree/bindings/mailbox/riscv,rpmi-shmem-mbox.yaml
> new file mode 100644
> index 000000000000..c339df5d9e24
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mailbox/riscv,rpmi-shmem-mbox.yaml
> @@ -0,0 +1,150 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mailbox/riscv,rpmi-shmem-mbox.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: RISC-V Platform Management Interface (RPMI) shared memory mailbox
> +
> +maintainers:
> +  - Anup Patel <anup@brainfault.org>
> +
> +description: |
> +  The RISC-V Platform Management Interface (RPMI) [1] defines a common shared
> +  memory based RPMI transport. This RPMI shared memory transport integrates as
> +  mailbox controller in the SBI implementation or supervisor software whereas
> +  each RPMI service group is mailbox client in the SBI implementation and
> +  supervisor software.
> +
> +  ===========================================
> +  References
> +  ===========================================
> +
> +  [1] RISC-V Platform Management Interface (RPMI)
> +      https://github.com/riscv-non-isa/riscv-rpmi/releases
> +
> +properties:
> +  compatible:
> +    const: riscv,rpmi-shmem-mbox
> +
> +  reg:
> +    oneOf:
> +      - items:
> +          - description: A2P request queue base address
> +          - description: P2A acknowledgment queue base address
> +          - description: P2A request queue base address
> +          - description: A2P acknowledgment queue base address
> +          - description: A2P doorbell address
> +      - items:
> +          - description: A2P request queue base address
> +          - description: P2A acknowledgment queue base address
> +          - description: P2A request queue base address
> +          - description: A2P acknowledgment queue base address
> +      - items:
> +          - description: A2P request queue base address
> +          - description: P2A acknowledgment queue base address
> +          - description: A2P doorbell address
> +      - items:
> +          - description: A2P request queue base address
> +          - description: P2A acknowledgment queue base address
> +
> +  reg-names:
> +    oneOf:
> +      - items:
> +          - const: a2p-req
> +          - const: p2a-ack
> +          - const: p2a-req
> +          - const: a2p-ack
> +          - const: doorbell
> +      - items:
> +          - const: a2p-req
> +          - const: p2a-ack
> +          - const: p2a-req
> +          - const: a2p-ack

These first 2 items lists can be combined with the addition of 
'minItems: 4'

> +      - items:
> +          - const: a2p-req
> +          - const: p2a-ack
> +          - const: doorbell
> +      - items:
> +          - const: a2p-req
> +          - const: p2a-ack
> +
> +  interrupts:
> +    maxItems: 1
> +    description:
> +      The RPMI shared memory transport supports wired interrupt specified by
> +      this property as the P2A doorbell.
> +
> +  msi-parent:
> +    description:
> +      The RPMI shared memory transport supports MSI as P2A doorbell and this
> +      property specifies the target MSI controller.
> +
> +  riscv,slot-size:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 64
> +    description:
> +      Power-of-2 RPMI slot size of the RPMI shared memory transport.
> +
> +  riscv,doorbell-mask:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    default: 0xffffffff
> +    description:
> +      Update only the register bits of doorbell defined by the mask (32 bit).
> +
> +  riscv,doorbell-value:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    default: 0x1
> +    description:
> +      Value written to the doorbell register bits (32-bit access) specified
> +      by the riscv,db-mask property.

You mean riscv,doorbell-mask?

I'm confused why you would need both? If the value to write is fixed 
here, then why do you need a mask? You could just mask the value here.

I assume there's some dependency between these 2 properties. That needs 
to be captured with 'dependencies'.

> +
> +  "#mbox-cells":
> +    const: 1
> +    description:
> +      The first cell specifies RPMI service group ID.
> +
> +required:
> +  - compatible
> +  - reg
> +  - reg-names
> +  - riscv,slot-size
> +  - "#mbox-cells"
> +
> +anyOf:
> +  - required:
> +      - interrupts
> +  - required:
> +      - msi-parent
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    // Example 1 (RPMI shared memory with only 2 queues):
> +    mailbox@10080000 {
> +        compatible = "riscv,rpmi-shmem-mbox";
> +        reg = <0x10080000 0x10000>,
> +              <0x10090000 0x10000>,
> +              <0x100a0000 0x4>;
> +        reg-names = "a2p-req", "p2a-ack", "doorbell";
> +        msi-parent = <&imsic_mlevel>;
> +        riscv,slot-size = <64>;
> +        #mbox-cells = <1>;
> +    };
> +  - |
> +    // Example 2 (RPMI shared memory with only 4 queues):
> +    mailbox@10001000 {
> +        compatible = "riscv,rpmi-shmem-mbox";
> +        reg = <0x10001000 0x800>,
> +              <0x10001800 0x800>,
> +              <0x10002000 0x800>,
> +              <0x10002800 0x800>,
> +              <0x10003000 0x4>;
> +        reg-names = "a2p-req", "p2a-ack", "p2a-req", "a2p-ack", "doorbell";
> +        msi-parent = <&imsic_mlevel>;
> +        riscv,slot-size = <64>;
> +        riscv,doorbell-mask = <0x00008000>;
> +        riscv,doorbell-value = <0x00008000>;
> +        #mbox-cells = <1>;
> +    };
> -- 
> 2.43.0
>