dt-bindings: clock: Add RPMI clock service message proxy bindings

# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)

%YAML 1.2

---

$id: http://devicetree.org/schemas/clock/riscv,rpmi-mpxy-clock.yaml#

$schema: http://devicetree.org/meta-schemas/core.yaml#

title: RISC-V RPMI clock service group based message proxy

maintainers:

  - Anup Patel <anup@brainfault.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 SBI implementation

  (machine mode firmware or hypervisor) can implement an SBI MPXY channel

  to allow RPMI clock service group access to the supervisor software.

  ===========================================

  References

  ===========================================

  [1] RISC-V Platform Management Interface (RPMI) v1.0 (or higher)

      https://github.com/riscv-non-isa/riscv-rpmi/releases

  [2] RISC-V Supervisor Binary Interface (SBI) v3.0 (or higher)

      https://github.com/riscv-non-isa/riscv-sbi-doc/releases

properties:

  compatible:

    description:

      Intended for use by the SBI implementation.

    const: riscv,rpmi-mpxy-clock

  mboxes:

    maxItems: 1

    description:

      Mailbox channel of the underlying RPMI transport.

  riscv,sbi-mpxy-channel-id:

    $ref: /schemas/types.yaml#/definitions/uint32

    description:

      The SBI MPXY channel id to be used for providing RPMI access to

      the supervisor software.

required:

  - compatible

  - mboxes

  - riscv,sbi-mpxy-channel-id

additionalProperties: false

examples:

  - |

    clock-service {

        compatible = "riscv,rpmi-mpxy-clock";

        mboxes = <&rpmi_shmem_mbox 0x8>;

        riscv,sbi-mpxy-channel-id = <0x1000>;

    };

...