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

[Anup Patel]

On Tue, Feb 4, 2025 at 4:00 AM Rob Herring <robh at kernel.org> wrote:
>
> 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 at 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 at 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'

It seems "minItems" is not allowed under "items".

If we put "minItems: 4" under "reg-names" then below
combinations become invalid.

>
> > +      - 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'.

We don't need the "riscv,doorbell-mask" property because the
latest frozen RPMI specification only defines a write-only 32-bit
doorbell register. I will remove this property in the next revision.

>
> > +
> > +  "#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 at 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 at 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
> >

Regards,
Anup