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