Documentation/devicetree/bindings/arm/psci.txt

   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
  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
  43 Main 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
  53 Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle
  54 state 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
  64 Example:
  65
  66 Case 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
  77 Case 2: PSCI v0.2 only
  78
  79         psci {
  80                 compatible      = "arm,psci-0.2";
  81                 method          = "smc";
  82         };
  83
  84 Case 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