1* Power State Coordination Interface (PSCI) 2 3Firmware implementing the PSCI functions described in ARM document number 4ARM DEN 0022A ("Power State Coordination Interface System Software on ARM 5processors") can be used by Linux to initiate various CPU-centric power 6operations. 7 8Issue A of the specification describes functions for CPU suspend, hotplug 9and migration of secure software. 10 11Functions are invoked by trapping to the privilege level of the PSCI 12firmware (specified as part of the binding below) and passing arguments 13in a manner similar to that specified by AAPCS: 14 15 r0 => 32-bit Function ID / return value 16 {r1 - r3} => Parameters 17 18Note that the immediate field of the trapping instruction must be set 19to #0. 20 21 22Main node required properties: 23 24 - compatible : should contain at least one of: 25 26 * "arm,psci" : for implementations complying to PSCI versions prior to 27 0.2. For these cases function IDs must be provided. 28 29 * "arm,psci-0.2" : for implementations complying to PSCI 0.2. Function 30 IDs are not required and should be ignored by an OS with PSCI 0.2 31 support, but are permitted to be present for compatibility with 32 existing software when "arm,psci" is later in the compatible list. 33 34 * "arm,psci-1.0" : for implementations complying to PSCI 1.0. PSCI 1.0 is 35 backward compatible with PSCI 0.2 with minor specification updates, 36 as defined in the PSCI specification[2]. 37 38 - method : The method of calling the PSCI firmware. Permitted 39 values are: 40 41 "smc" : SMC #0, with the register assignments specified 42 in this binding. 43 44 "hvc" : HVC #0, with the register assignments specified 45 in this binding. 46 47Main node optional properties: 48 49 - cpu_suspend : Function ID for CPU_SUSPEND operation 50 51 - cpu_off : Function ID for CPU_OFF operation 52 53 - cpu_on : Function ID for CPU_ON operation 54 55 - migrate : Function ID for MIGRATE operation 56 57Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle 58state nodes, as per bindings in [1]) must specify the following properties: 59 60- arm,psci-suspend-param 61 Usage: Required for state nodes[1] if the corresponding 62 idle-states node entry-method property is set 63 to "psci". 64 Value type: <u32> 65 Definition: power_state parameter to pass to the PSCI 66 suspend call. 67 68Example: 69 70Case 1: PSCI v0.1 only. 71 72 psci { 73 compatible = "arm,psci"; 74 method = "smc"; 75 cpu_suspend = <0x95c10000>; 76 cpu_off = <0x95c10001>; 77 cpu_on = <0x95c10002>; 78 migrate = <0x95c10003>; 79 }; 80 81Case 2: PSCI v0.2 only 82 83 psci { 84 compatible = "arm,psci-0.2"; 85 method = "smc"; 86 }; 87 88Case 3: PSCI v0.2 and PSCI v0.1. 89 90 A DTB may provide IDs for use by kernels without PSCI 0.2 support, 91 enabling firmware and hypervisors to support existing and new kernels. 92 These IDs will be ignored by kernels with PSCI 0.2 support, which will 93 use the standard PSCI 0.2 IDs exclusively. 94 95 psci { 96 compatible = "arm,psci-0.2", "arm,psci"; 97 method = "hvc"; 98 99 cpu_on = < arbitrary value >; 100 cpu_off = < arbitrary value >; 101 102 ... 103 }; 104 105[1] Kernel documentation - ARM idle states bindings 106 Documentation/devicetree/bindings/arm/idle-states.txt 107[2] Power State Coordination Interface (PSCI) specification 108 http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf 109