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Will Deacon65397ed2012-12-11 17:28:27 +00001* 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
Ashwin Chaugulee1cd3b32014-03-27 11:08:57 -040024 - compatible : should contain at least one of:
25
Geert Uytterhoeven414ee532015-12-15 10:55:59 +010026 * "arm,psci" : For implementations complying to PSCI versions prior
27 to 0.2.
28 For these cases function IDs must be provided.
Ashwin Chaugulee1cd3b32014-03-27 11:08:57 -040029
Geert Uytterhoeven414ee532015-12-15 10:55:59 +010030 * "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.
Will Deacon65397ed2012-12-11 17:28:27 +000035
Geert Uytterhoeven414ee532015-12-15 10:55:59 +010036 * "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].
Lorenzo Pieralisi0fc197c2015-05-26 13:06:57 +010040
Will Deacon65397ed2012-12-11 17:28:27 +000041 - 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
Lorenzo Pieralisi3f8161b2013-11-27 16:22:55 +000060Device 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.
Will Deacon65397ed2012-12-11 17:28:27 +000070
71Example:
72
Ashwin Chaugulee1cd3b32014-03-27 11:08:57 -040073Case 1: PSCI v0.1 only.
74
Will Deacon65397ed2012-12-11 17:28:27 +000075 psci {
76 compatible = "arm,psci";
77 method = "smc";
78 cpu_suspend = <0x95c10000>;
79 cpu_off = <0x95c10001>;
80 cpu_on = <0x95c10002>;
81 migrate = <0x95c10003>;
82 };
Ashwin Chaugulee1cd3b32014-03-27 11:08:57 -040083
Ashwin Chaugulee1cd3b32014-03-27 11:08:57 -040084Case 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 };
Lorenzo Pieralisi3f8161b2013-11-27 16:22:55 +0000107
108[1] Kernel documentation - ARM idle states bindings
109 Documentation/devicetree/bindings/arm/idle-states.txt
Lorenzo Pieralisi0fc197c2015-05-26 13:06:57 +0100110[2] Power State Coordination Interface (PSCI) specification
111 http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf