# 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.
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.
minItems: 1
items:
- const: arm,psci-0.2
- const: arm,psci
- 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].
minItems: 1
items:
- const: arm,psci-1.0
- const: arm,psci-0.2
- const: arm,psci
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/cpu/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>;
};
};
...
