* Power State Coordination Interface (PSCI) 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. Main node required properties: - compatible : should contain at least one of: * "arm,psci" : For implementations complying to PSCI versions prior to 0.2. For these cases function IDs must be provided. * "arm,psci-0.2" : 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. * "arm,psci-1.0" : 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]. - method : The method of calling the PSCI firmware. Permitted values are: "smc" : SMC #0, with the register assignments specified in this binding. "hvc" : HVC #0, with the register assignments specified in this binding. Main node optional properties: - cpu_suspend : Function ID for CPU_SUSPEND operation - cpu_off : Function ID for CPU_OFF operation - cpu_on : Function ID for CPU_ON operation - migrate : Function ID for MIGRATE operation Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle state nodes, as per bindings in [1]) must specify the following properties: - arm,psci-suspend-param Usage: Required for state nodes[1] if the corresponding idle-states node entry-method property is set to "psci". Value type: Definition: power_state parameter to pass to the PSCI suspend call. Example: 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 = < arbitrary value >; cpu_off = < arbitrary value >; ... }; [1] Kernel documentation - ARM idle states bindings Documentation/devicetree/bindings/arm/idle-states.txt [2] Power State Coordination Interface (PSCI) specification http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf