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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
27			to 0.2.
28			For these cases function IDs must be provided.
29
30     * "arm,psci-0.2" : For implementations complying to PSCI 0.2.
31			Function IDs are not required and should be ignored by
32			an OS with PSCI 0.2 support, but are permitted to be
33			present for compatibility with existing software when
34			"arm,psci" is later in the compatible list.
35
36     * "arm,psci-1.0" : For implementations complying to PSCI 1.0.
37			PSCI 1.0 is backward compatible with PSCI 0.2 with
38			minor specification updates, as defined in the PSCI
39			specification[2].
40
41 - method        : The method of calling the PSCI firmware. Permitted
42                   values are:
43
44                   "smc" : SMC #0, with the register assignments specified
45		           in this binding.
46
47                   "hvc" : HVC #0, with the register assignments specified
48		           in this binding.
49
50Main node optional properties:
51
52 - cpu_suspend   : Function ID for CPU_SUSPEND operation
53
54 - cpu_off       : Function ID for CPU_OFF operation
55
56 - cpu_on        : Function ID for CPU_ON operation
57
58 - migrate       : Function ID for MIGRATE operation
59
60Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle
61state nodes, as per bindings in [1]) must specify the following properties:
62
63- arm,psci-suspend-param
64		Usage: Required for state nodes[1] if the corresponding
65                       idle-states node entry-method property is set
66                       to "psci".
67		Value type: <u32>
68		Definition: power_state parameter to pass to the PSCI
69			    suspend call.
70
71Example:
72
73Case 1: PSCI v0.1 only.
74
75	psci {
76		compatible	= "arm,psci";
77		method		= "smc";
78		cpu_suspend	= <0x95c10000>;
79		cpu_off		= <0x95c10001>;
80		cpu_on		= <0x95c10002>;
81		migrate		= <0x95c10003>;
82	};
83
84Case 2: PSCI v0.2 only
85
86	psci {
87		compatible	= "arm,psci-0.2";
88		method		= "smc";
89	};
90
91Case 3: PSCI v0.2 and PSCI v0.1.
92
93	A DTB may provide IDs for use by kernels without PSCI 0.2 support,
94	enabling firmware and hypervisors to support existing and new kernels.
95	These IDs will be ignored by kernels with PSCI 0.2 support, which will
96	use the standard PSCI 0.2 IDs exclusively.
97
98	psci {
99		compatible = "arm,psci-0.2", "arm,psci";
100		method = "hvc";
101
102		cpu_on = < arbitrary value >;
103		cpu_off = < arbitrary value >;
104
105		...
106	};
107
108[1] Kernel documentation - ARM idle states bindings
109    Documentation/devicetree/bindings/arm/idle-states.txt
110[2] Power State Coordination Interface (PSCI) specification
111    http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
112