Will Deacon | 65397ed | 2012-12-11 17:28:27 +0000 | [diff] [blame] | 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 | |
Ashwin Chaugule | e1cd3b3 | 2014-03-27 11:08:57 -0400 | [diff] [blame] | 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. |
Will Deacon | 65397ed | 2012-12-11 17:28:27 +0000 | [diff] [blame] | 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 | |
Lorenzo Pieralisi | 3f8161b | 2013-11-27 16:22:55 +0000 | [diff] [blame] | 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. |
Will Deacon | 65397ed | 2012-12-11 17:28:27 +0000 | [diff] [blame] | 63 | |
| 64 | Example: |
| 65 | |
Ashwin Chaugule | e1cd3b3 | 2014-03-27 11:08:57 -0400 | [diff] [blame] | 66 | Case 1: PSCI v0.1 only. |
| 67 | |
Will Deacon | 65397ed | 2012-12-11 17:28:27 +0000 | [diff] [blame] | 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 | }; |
Ashwin Chaugule | e1cd3b3 | 2014-03-27 11:08:57 -0400 | [diff] [blame] | 76 | |
Ashwin Chaugule | e1cd3b3 | 2014-03-27 11:08:57 -0400 | [diff] [blame] | 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 | }; |
Lorenzo Pieralisi | 3f8161b | 2013-11-27 16:22:55 +0000 | [diff] [blame] | 100 | |
| 101 | [1] Kernel documentation - ARM idle states bindings |
| 102 | Documentation/devicetree/bindings/arm/idle-states.txt |