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65397edf WD |
1 | * Power State Coordination Interface (PSCI) |
2 | ||
3 | Firmware implementing the PSCI functions described in ARM document number | |
4 | ARM DEN 0022A ("Power State Coordination Interface System Software on ARM | |
5 | processors") can be used by Linux to initiate various CPU-centric power | |
6 | operations. | |
7 | ||
8 | Issue A of the specification describes functions for CPU suspend, hotplug | |
9 | and migration of secure software. | |
10 | ||
11 | Functions are invoked by trapping to the privilege level of the PSCI | |
12 | firmware (specified as part of the binding below) and passing arguments | |
13 | in a manner similar to that specified by AAPCS: | |
14 | ||
15 | r0 => 32-bit Function ID / return value | |
16 | {r1 - r3} => Parameters | |
17 | ||
18 | Note that the immediate field of the trapping instruction must be set | |
19 | to #0. | |
20 | ||
21 | ||
22 | Main node required properties: | |
23 | ||
e1cd3b36 AC |
24 | - compatible : should contain at least one of: |
25 | ||
414ee536 GU |
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]. | |
0fc197c7 | 40 | |
65397edf WD |
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 | ||
50 | Main 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 | ||
3f8161b2 LP |
60 | Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle |
61 | state 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. | |
65397edf WD |
70 | |
71 | Example: | |
72 | ||
e1cd3b36 AC |
73 | Case 1: PSCI v0.1 only. |
74 | ||
65397edf WD |
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 | }; | |
e1cd3b36 | 83 | |
e1cd3b36 AC |
84 | Case 2: PSCI v0.2 only |
85 | ||
86 | psci { | |
87 | compatible = "arm,psci-0.2"; | |
88 | method = "smc"; | |
89 | }; | |
90 | ||
91 | Case 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 | }; | |
3f8161b2 LP |
107 | |
108 | [1] Kernel documentation - ARM idle states bindings | |
109 | Documentation/devicetree/bindings/arm/idle-states.txt | |
0fc197c7 LP |
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 |