112 lines
3.4 KiB
Plaintext
112 lines
3.4 KiB
Plaintext
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* Power State Coordination Interface (PSCI)
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Firmware implementing the PSCI functions described in ARM document number
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ARM DEN 0022A ("Power State Coordination Interface System Software on ARM
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processors") can be used by Linux to initiate various CPU-centric power
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operations.
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Issue A of the specification describes functions for CPU suspend, hotplug
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and migration of secure software.
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Functions are invoked by trapping to the privilege level of the PSCI
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firmware (specified as part of the binding below) and passing arguments
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in a manner similar to that specified by AAPCS:
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r0 => 32-bit Function ID / return value
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{r1 - r3} => Parameters
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Note that the immediate field of the trapping instruction must be set
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to #0.
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Main node required properties:
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- compatible : should contain at least one of:
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* "arm,psci" : For implementations complying to PSCI versions prior
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to 0.2.
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For these cases function IDs must be provided.
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* "arm,psci-0.2" : For implementations complying to PSCI 0.2.
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Function IDs are not required and should be ignored by
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an OS with PSCI 0.2 support, but are permitted to be
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present for compatibility with existing software when
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"arm,psci" is later in the compatible list.
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* "arm,psci-1.0" : For implementations complying to PSCI 1.0.
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PSCI 1.0 is backward compatible with PSCI 0.2 with
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minor specification updates, as defined in the PSCI
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specification[2].
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- method : The method of calling the PSCI firmware. Permitted
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values are:
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"smc" : SMC #0, with the register assignments specified
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in this binding.
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"hvc" : HVC #0, with the register assignments specified
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in this binding.
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Main node optional properties:
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- cpu_suspend : Function ID for CPU_SUSPEND operation
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- cpu_off : Function ID for CPU_OFF operation
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- cpu_on : Function ID for CPU_ON operation
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- migrate : Function ID for MIGRATE operation
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Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle
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state nodes, as per bindings in [1]) must specify the following properties:
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- arm,psci-suspend-param
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Usage: Required for state nodes[1] if the corresponding
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idle-states node entry-method property is set
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to "psci".
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Value type: <u32>
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Definition: power_state parameter to pass to the PSCI
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suspend call.
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Example:
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Case 1: PSCI v0.1 only.
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psci {
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compatible = "arm,psci";
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method = "smc";
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cpu_suspend = <0x95c10000>;
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cpu_off = <0x95c10001>;
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cpu_on = <0x95c10002>;
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migrate = <0x95c10003>;
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};
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Case 2: PSCI v0.2 only
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psci {
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compatible = "arm,psci-0.2";
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method = "smc";
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};
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Case 3: PSCI v0.2 and PSCI v0.1.
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A DTB may provide IDs for use by kernels without PSCI 0.2 support,
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enabling firmware and hypervisors to support existing and new kernels.
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These IDs will be ignored by kernels with PSCI 0.2 support, which will
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use the standard PSCI 0.2 IDs exclusively.
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psci {
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compatible = "arm,psci-0.2", "arm,psci";
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method = "hvc";
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cpu_on = < arbitrary value >;
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cpu_off = < arbitrary value >;
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...
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};
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[1] Kernel documentation - ARM idle states bindings
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Documentation/devicetree/bindings/arm/idle-states.txt
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[2] Power State Coordination Interface (PSCI) specification
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http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
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