dt-bindings: clock: Add RPMI clock service controller bindings

# 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@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 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) 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 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

    description:

      Platform specific CLOCK_ID as defined by the RISC-V Platform Management

      Interface (RPMI) specification.

required:

  - compatible

  - mboxes

  - "#clock-cells"

additionalProperties: false

examples:

  - |

    clock-controller {

        compatible = "riscv,rpmi-clock";

        mboxes = <&mpxy_mbox 0x1000 0x0>;

        #clock-cells = <1>;

    };

...