linux/Documentation/devicetree/bindings/arm/psci.yaml

# SPDX-License-Identifier: GPL-2.0
%YAML 1.2
---
$id: http://devicetree.org/schemas/arm/psci.yaml#
$schema: http://devicetree.org/meta-schemas/core.yaml#

title: Power State Coordination Interface (PSCI)

maintainers:
  - Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

description: |+
  Firmware implementing the PSCI functions described in ARM document number
  ARM DEN 0022A ("Power State Coordination Interface System Software on ARM
  processors") can be used by Linux to initiate various CPU-centric power
  operations.

  Issue A of the specification describes functions for CPU suspend, hotplug
  and migration of secure software.

  Functions are invoked by trapping to the privilege level of the PSCI
  firmware (specified as part of the binding below) and passing arguments
  in a manner similar to that specified by AAPCS:

     r0       => 32-bit Function ID / return value
    {r1 - r3}	=> Parameters

  Note that the immediate field of the trapping instruction must be set
  to #0.

  [2] Power State Coordination Interface (PSCI) specification
    http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf  

properties:
  $nodename:
    const: psci

  compatible:
    oneOf:
      - description:
          For implementations complying to PSCI versions prior to 0.2.
        const: arm,psci

      - description:
          For implementations complying to PSCI 0.2.
        const: arm,psci-0.2

      - description:
          For implementations complying to PSCI 0.2.
          Function IDs are not required and should be ignored by an OS with
          PSCI 0.2 support, but are permitted to be present for compatibility
          with existing software when "arm,psci" is later in the compatible
          list.
        items:
          - const: arm,psci-0.2
          - const: arm,psci

      - description:
          For implementations complying to PSCI 1.0.
        const: arm,psci-1.0

      - description:
          For implementations complying to PSCI 1.0.
          PSCI 1.0 is backward compatible with PSCI 0.2 with minor
          specification updates, as defined in the PSCI specification[2].
        items:
          - const: arm,psci-1.0
          - const: arm,psci-0.2

  method:
    description: The method of calling the PSCI firmware.
    $ref: /schemas/types.yaml#/definitions/string-array
    enum:
      - smc
      # HVC #0, with the register assignments specified in this binding.
      - hvc

  cpu_suspend:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: Function ID for CPU_SUSPEND operation

  cpu_off:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: Function ID for CPU_OFF operation

  cpu_on:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: Function ID for CPU_ON operation

  migrate:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: Function ID for MIGRATE operation

  arm,psci-suspend-param:
    $ref: /schemas/types.yaml#/definitions/uint32
    description: |
      power_state parameter to pass to the PSCI suspend call.

      Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie
      idle state nodes with entry-method property is set to "psci", as per
      bindings in [1]) must specify this property.

      [1] Kernel documentation - ARM idle states bindings
        Documentation/devicetree/bindings/arm/idle-states.yaml      

patternProperties:
  "^power-domain-":
    $ref: "../power/power-domain.yaml#"

    type: object
    description: |
      ARM systems can have multiple cores, sometimes in an hierarchical
      arrangement. This often, but not always, maps directly to the processor
      power topology of the system. Individual nodes in a topology have their
      own specific power states and can be better represented hierarchically.

      For these cases, the definitions of the idle states for the CPUs and the
      CPU topology, must conform to the binding in [3]. The idle states
      themselves must conform to the binding in [4] and must specify the
      arm,psci-suspend-param property.

      It should also be noted that, in PSCI firmware v1.0 the OS-Initiated
      (OSI) CPU suspend mode is introduced. Using a hierarchical representation
      helps to implement support for OSI mode and OS implementations may choose
      to mandate it.

      [3] Documentation/devicetree/bindings/power/power-domain.yaml
      [4] Documentation/devicetree/bindings/power/domain-idle-state.yaml      

required:
  - compatible
  - method

allOf:
  - if:
      properties:
        compatible:
          contains:
            const: arm,psci
    then:
      required:
        - cpu_off
        - cpu_on

additionalProperties: false

examples:
  - |+

    // Case 1: PSCI v0.1 only.

    psci {
      compatible      = "arm,psci";
      method          = "smc";
      cpu_suspend     = <0x95c10000>;
      cpu_off         = <0x95c10001>;
      cpu_on          = <0x95c10002>;
      migrate         = <0x95c10003>;
    };

  - |+

    // Case 2: PSCI v0.2 only

    psci {
      compatible      = "arm,psci-0.2";
      method          = "smc";
    };


  - |+

    // Case 3: PSCI v0.2 and PSCI v0.1.

    /*
     * A DTB may provide IDs for use by kernels without PSCI 0.2 support,
     * enabling firmware and hypervisors to support existing and new kernels.
     * These IDs will be ignored by kernels with PSCI 0.2 support, which will
     * use the standard PSCI 0.2 IDs exclusively.
     */

    psci {
      compatible = "arm,psci-0.2", "arm,psci";
      method = "hvc";

      cpu_on = <0x95c10002>;
      cpu_off = <0x95c10001>;
    };

  - |+

    // Case 4: CPUs and CPU idle states described using the hierarchical model.

    cpus {
      #size-cells = <0>;
      #address-cells = <1>;

      CPU0: cpu@0 {
        device_type = "cpu";
        compatible = "arm,cortex-a53";
        reg = <0x0>;
        enable-method = "psci";
        power-domains = <&CPU_PD0>;
        power-domain-names = "psci";
      };

      CPU1: cpu@1 {
        device_type = "cpu";
        compatible = "arm,cortex-a53";
        reg = <0x100>;
        enable-method = "psci";
        power-domains = <&CPU_PD1>;
        power-domain-names = "psci";
      };

      idle-states {

        CPU_PWRDN: cpu-power-down {
          compatible = "arm,idle-state";
          arm,psci-suspend-param = <0x0000001>;
          entry-latency-us = <10>;
          exit-latency-us = <10>;
          min-residency-us = <100>;
        };
      };

      domain-idle-states {

        CLUSTER_RET: cluster-retention {
          compatible = "domain-idle-state";
          arm,psci-suspend-param = <0x1000011>;
          entry-latency-us = <500>;
          exit-latency-us = <500>;
          min-residency-us = <2000>;
        };

        CLUSTER_PWRDN: cluster-power-down {
          compatible = "domain-idle-state";
          arm,psci-suspend-param = <0x1000031>;
          entry-latency-us = <2000>;
          exit-latency-us = <2000>;
          min-residency-us = <6000>;
        };
      };
    };

    psci {
      compatible = "arm,psci-1.0";
      method = "smc";

      CPU_PD0: power-domain-cpu0 {
        #power-domain-cells = <0>;
        domain-idle-states = <&CPU_PWRDN>;
        power-domains = <&CLUSTER_PD>;
      };

      CPU_PD1: power-domain-cpu1 {
        #power-domain-cells = <0>;
        domain-idle-states =  <&CPU_PWRDN>;
        power-domains = <&CLUSTER_PD>;
      };

      CLUSTER_PD: power-domain-cluster {
        #power-domain-cells = <0>;
        domain-idle-states = <&CLUSTER_RET>, <&CLUSTER_PWRDN>;
      };
    };
...