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Diffstat (limited to 'Documentation/devicetree/bindings/arm/psci.txt')
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diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt new file mode 100644 index 000000000..a2c4f1d52 --- /dev/null +++ b/Documentation/devicetree/bindings/arm/psci.txt @@ -0,0 +1,111 @@ +* 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: <u32> + 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 |