Documentation/thermal/sysfs-api.txt

   1 Generic Thermal Sysfs driver How To
   2 =========================
   3
   4 Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
   5
   6 Updated: 2 January 2008
   7
   8 Copyright (c)  2008 Intel Corporation
   9
  10
  11 0. Introduction
  12
  13 The generic thermal sysfs provides a set of interfaces for thermal zone devices (sensors)
  14 and thermal cooling devices (fan, processor...) to register with the thermal management
  15 solution and to be a part of it.
  16
  17 This how-to focuses on enabling new thermal zone and cooling devices to participate
  18 in thermal management.
  19 This solution is platform independent and any type of thermal zone devices and
  20 cooling devices should be able to make use of the infrastructure.
  21
  22 The main task of the thermal sysfs driver is to expose thermal zone attributes as well
  23 as cooling device attributes to the user space.
  24 An intelligent thermal management application can make decisions based on inputs
  25 from thermal zone attributes (the current temperature and trip point temperature)
  26 and throttle appropriate devices.
  27
  28 [0-*]   denotes any positive number starting from 0
  29 [1-*]   denotes any positive number starting from 1
  30
  31 1. thermal sysfs driver interface functions
  32
  33 1.1 thermal zone device interface
  34 1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name, int trips,
  35                                 void *devdata, struct thermal_zone_device_ops *ops)
  36
  37         This interface function adds a new thermal zone device (sensor) to
  38         /sys/class/thermal folder as thermal_zone[0-*].
  39         It tries to bind all the thermal cooling devices registered at the same time.
  40
  41         name: the thermal zone name.
  42         trips: the total number of trip points this thermal zone supports.
  43         devdata: device private data
  44         ops: thermal zone device call-backs.
  45                 .bind: bind the thermal zone device with a thermal cooling device.
  46                 .unbind: unbind the thermal zone device with a thermal cooling device.
  47                 .get_temp: get the current temperature of the thermal zone.
  48                 .get_mode: get the current mode (user/kernel) of the thermal zone.
  49                            "kernel" means thermal management is done in kernel.
  50                            "user" will prevent kernel thermal driver actions upon trip points
  51                            so that user applications can take charge of thermal management.
  52                 .set_mode: set the mode (user/kernel) of the thermal zone.
  53                 .get_trip_type: get the type of certain trip point.
  54                 .get_trip_temp: get the temperature above which the certain trip point
  55                                 will be fired.
  56
  57 1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  58
  59         This interface function removes the thermal zone device.
  60         It deletes the corresponding entry form /sys/class/thermal folder and unbind all
  61         the thermal cooling devices it uses.
  62
  63 1.2 thermal cooling device interface
  64 1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
  65                                         void *devdata, struct thermal_cooling_device_ops *)
  66
  67         This interface function adds a new thermal cooling device (fan/processor/...) to
  68         /sys/class/thermal/ folder as cooling_device[0-*].
  69         It tries to bind itself to all the thermal zone devices register at the same time.
  70         name: the cooling device name.
  71         devdata: device private data.
  72         ops: thermal cooling devices call-backs.
  73                 .get_max_state: get the Maximum throttle state of the cooling device.
  74                 .get_cur_state: get the Current throttle state of the cooling device.
  75                 .set_cur_state: set the Current throttle state of the cooling device.
  76
  77 1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  78
  79         This interface function remove the thermal cooling device.
  80         It deletes the corresponding entry form /sys/class/thermal folder and unbind
  81         itself from all the thermal zone devices using it.
  82
  83 1.3 interface for binding a thermal zone device with a thermal cooling device
  84 1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
  85                         int trip, struct thermal_cooling_device *cdev);
  86
  87         This interface function bind a thermal cooling device to the certain trip point
  88         of a thermal zone device.
  89         This function is usually called in the thermal zone device .bind callback.
  90         tz: the thermal zone device
  91         cdev: thermal cooling device
  92         trip: indicates which trip point the cooling devices is associated with
  93                  in this thermal zone.
  94
  95 1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
  96                                 int trip, struct thermal_cooling_device *cdev);
  97
  98         This interface function unbind a thermal cooling device from the certain trip point
  99         of a thermal zone device.
 100         This function is usually called in the thermal zone device .unbind callback.
 101         tz: the thermal zone device
 102         cdev: thermal cooling device
 103         trip: indicates which trip point the cooling devices is associated with
 104                 in this thermal zone.
 105
 106 2. sysfs attributes structure
 107
 108 RO      read only value
 109 RW      read/write value
 110
 111 All thermal sysfs attributes will be represented under /sys/class/thermal
 112
 113 Thermal zone device sys I/F, created once it's registered:
 114 |thermal_zone[0-*]:
 115         |-----type:                     Type of the thermal zone
 116         |-----temp:                     Current temperature
 117         |-----mode:                     Working mode of the thermal zone
 118         |-----trip_point_[0-*]_temp:    Trip point temperature
 119         |-----trip_point_[0-*]_type:    Trip point type
 120
 121 Thermal cooling device sys I/F, created once it's registered:
 122 |cooling_device[0-*]:
 123         |-----type :                    Type of the cooling device(processor/fan/...)
 124         |-----max_state:                Maximum cooling state of the cooling device
 125         |-----cur_state:                Current cooling state of the cooling device
 126
 127
 128 These two dynamic attributes are created/removed in pairs.
 129 They represent the relationship between a thermal zone and its associated cooling device.
 130 They are created/removed for each
 131 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful execution.
 132
 133 |thermal_zone[0-*]
 134         |-----cdev[0-*]:                The [0-*]th cooling device in the current thermal zone
 135         |-----cdev[0-*]_trip_point:     Trip point that cdev[0-*] is associated with
 136
 137
 138 ***************************
 139 * Thermal zone attributes *
 140 ***************************
 141
 142 type                            Strings which represent the thermal zone type.
 143                                 This is given by thermal zone driver as part of registration.
 144                                 Eg: "ACPI thermal zone" indicates it's a ACPI thermal device
 145                                 RO
 146                                 Required
 147
 148 temp                            Current temperature as reported by thermal zone (sensor)
 149                                 Unit: millidegree Celsius
 150                                 RO
 151                                 Required
 152
 153 mode                            One of the predefined values in [kernel, user]
 154                                 This file gives information about the algorithm
 155                                 that is currently managing the thermal zone.
 156                                 It can be either default kernel based algorithm
 157                                 or user space application.
 158                                 RW
 159                                 Optional
 160                                 kernel  = Thermal management in kernel thermal zone driver.
 161                                 user    = Preventing kernel thermal zone driver actions upon
 162                                           trip points so that user application can take full
 163                                           charge of the thermal management.
 164
 165 trip_point_[0-*]_temp           The temperature above which trip point will be fired
 166                                 Unit: millidegree Celsius
 167                                 RO
 168                                 Optional
 169
 170 trip_point_[0-*]_type           Strings which indicate the type of the trip point
 171                                 E.g. it can be one of critical, hot, passive,
 172                                     active[0-*] for ACPI thermal zone.
 173                                 RO
 174                                 Optional
 175
 176 cdev[0-*]                       Sysfs link to the thermal cooling device node where the sys I/F
 177                                 for cooling device throttling control represents.
 178                                 RO
 179                                 Optional
 180
 181 cdev[0-*]_trip_point            The trip point with which cdev[0-*] is associated in this thermal zone
 182                                 -1 means the cooling device is not associated with any trip point.
 183                                 RO
 184                                 Optional
 185
 186 ******************************
 187 * Cooling device  attributes *
 188 ******************************
 189
 190 type                            String which represents the type of device
 191                                 eg: For generic ACPI: this should be "Fan",
 192                                 "Processor" or "LCD"
 193                                 eg. For memory controller device on intel_menlow platform:
 194                                 this should be "Memory controller"
 195                                 RO
 196                                 Required
 197
 198 max_state                       The maximum permissible cooling state of this cooling device.
 199                                 RO
 200                                 Required
 201
 202 cur_state                       The current cooling state of this cooling device.
 203                                 the value can any integer numbers between 0 and max_state,
 204                                 cur_state == 0 means no cooling
 205                                 cur_state == max_state means the maximum cooling.
 206                                 RW
 207                                 Required
 208
 209 3. A simple implementation
 210
 211 ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
 212 If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
 213 it may register itself as a thermal_zone_device (thermal_zone1) with 4 trip points in all.
 214 It has one processor and one fan, which are both registered as thermal_cooling_device.
 215 If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
 216 the sys I/F structure will be built like this:
 217
 218 /sys/class/thermal:
 219
 220 |thermal_zone1:
 221         |-----type:                     ACPI thermal zone
 222         |-----temp:                     37000
 223         |-----mode:                     kernel
 224         |-----trip_point_0_temp:        100000
 225         |-----trip_point_0_type:        critical
 226         |-----trip_point_1_temp:        80000
 227         |-----trip_point_1_type:        passive
 228         |-----trip_point_2_temp:        70000
 229         |-----trip_point_2_type:        active0
 230         |-----trip_point_3_temp:        60000
 231         |-----trip_point_3_type:        active1
 232         |-----cdev0:                    --->/sys/class/thermal/cooling_device0
 233         |-----cdev0_trip_point:         1       /* cdev0 can be used for passive */
 234         |-----cdev1:                    --->/sys/class/thermal/cooling_device3
 235         |-----cdev1_trip_point:         2       /* cdev1 can be used for active[0]*/
 236
 237 |cooling_device0:
 238         |-----type:                     Processor
 239         |-----max_state:                8
 240         |-----cur_state:                0
 241
 242 |cooling_device3:
 243         |-----type:                     Fan
 244         |-----max_state:                2
 245         |-----cur_state:                0