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 - method        : The method of calling the PSCI firmware. Permitted
35                   values are:
36
37                   "smc" : SMC #0, with the register assignments specified
38		           in this binding.
39
40                   "hvc" : HVC #0, with the register assignments specified
41		           in this binding.
42
43Main node optional properties:
44
45 - cpu_suspend   : Function ID for CPU_SUSPEND operation
46
47 - cpu_off       : Function ID for CPU_OFF operation
48
49 - cpu_on        : Function ID for CPU_ON operation
50
51 - migrate       : Function ID for MIGRATE operation
52
53Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle
54state nodes, as per bindings in [1]) must specify the following properties:
55
56- arm,psci-suspend-param
57		Usage: Required for state nodes[1] if the corresponding
58                       idle-states node entry-method property is set
59                       to "psci".
60		Value type: <u32>
61		Definition: power_state parameter to pass to the PSCI
62			    suspend call.
63
64Example:
65
66Case 1: PSCI v0.1 only.
67
68	psci {
69		compatible	= "arm,psci";
70		method		= "smc";
71		cpu_suspend	= <0x95c10000>;
72		cpu_off		= <0x95c10001>;
73		cpu_on		= <0x95c10002>;
74		migrate		= <0x95c10003>;
75	};
76
77Case 2: PSCI v0.2 only
78
79	psci {
80		compatible	= "arm,psci-0.2";
81		method		= "smc";
82	};
83
84Case 3: PSCI v0.2 and PSCI v0.1.
85
86	A DTB may provide IDs for use by kernels without PSCI 0.2 support,
87	enabling firmware and hypervisors to support existing and new kernels.
88	These IDs will be ignored by kernels with PSCI 0.2 support, which will
89	use the standard PSCI 0.2 IDs exclusively.
90
91	psci {
92		compatible = "arm,psci-0.2", "arm,psci";
93		method = "hvc";
94
95		cpu_on = < arbitrary value >;
96		cpu_off = < arbitrary value >;
97
98		...
99	};
100
101[1] Kernel documentation - ARM idle states bindings
102    Documentation/devicetree/bindings/arm/idle-states.txt
103