linux/Documentation/thermal/sysfs-api.txt
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   1Generic Thermal Sysfs driver How To
   2===================================
   3
   4Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
   5
   6Updated: 2 January 2008
   7
   8Copyright (c)  2008 Intel Corporation
   9
  10
  110. Introduction
  12
  13The generic thermal sysfs provides a set of interfaces for thermal zone
  14devices (sensors) and thermal cooling devices (fan, processor...) to register
  15with the thermal management solution and to be a part of it.
  16
  17This how-to focuses on enabling new thermal zone and cooling devices to
  18participate in thermal management.
  19This solution is platform independent and any type of thermal zone devices
  20and cooling devices should be able to make use of the infrastructure.
  21
  22The main task of the thermal sysfs driver is to expose thermal zone attributes
  23as well as cooling device attributes to the user space.
  24An intelligent thermal management application can make decisions based on
  25inputs from thermal zone attributes (the current temperature and trip point
  26temperature) and throttle appropriate devices.
  27
  28[0-*]   denotes any positive number starting from 0
  29[1-*]   denotes any positive number starting from 1
  30
  311. thermal sysfs driver interface functions
  32
  331.1 thermal zone device interface
  341.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name,
  35                int trips, 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-*]. It tries to bind all the
  39    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
  571.1.2 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
  61    unbind all the thermal cooling devices it uses.
  62
  631.2 thermal cooling device interface
  641.2.1 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/...)
  68    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
  69    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
  771.2.2 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
  81    unbind itself from all the thermal zone devices using it.
  82
  831.3 interface for binding a thermal zone device with a thermal cooling device
  841.3.1 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
  88    point 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
  951.3.2 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
  99    trip point of a thermal zone device. This function is usually called in
 100    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
 1062. sysfs attributes structure
 107
 108RO      read only value
 109RW      read/write value
 110
 111Thermal sysfs attributes will be represented under /sys/class/thermal.
 112Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 113if hwmon is compiled in or built as a module.
 114
 115Thermal zone device sys I/F, created once it's registered:
 116/sys/class/thermal/thermal_zone[0-*]:
 117    |---type:                   Type of the thermal zone
 118    |---temp:                   Current temperature
 119    |---mode:                   Working mode of the thermal zone
 120    |---trip_point_[0-*]_temp:  Trip point temperature
 121    |---trip_point_[0-*]_type:  Trip point type
 122
 123Thermal cooling device sys I/F, created once it's registered:
 124/sys/class/thermal/cooling_device[0-*]:
 125    |---type:                   Type of the cooling device(processor/fan/...)
 126    |---max_state:              Maximum cooling state of the cooling device
 127    |---cur_state:              Current cooling state of the cooling device
 128
 129
 130Then next two dynamic attributes are created/removed in pairs. They represent
 131the relationship between a thermal zone and its associated cooling device.
 132They are created/removed for each successful execution of
 133thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 134
 135/sys/class/thermal/thermal_zone[0-*]:
 136    |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 137    |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 138
 139Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 140the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 141of thermal zone device. E.g. the generic thermal driver registers one hwmon
 142class device and build the associated hwmon sysfs I/F for all the registered
 143ACPI thermal zones.
 144
 145/sys/class/hwmon/hwmon[0-*]:
 146    |---name:                   The type of the thermal zone devices
 147    |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 148    |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 149
 150Please read Documentation/hwmon/sysfs-interface for additional information.
 151
 152***************************
 153* Thermal zone attributes *
 154***************************
 155
 156type
 157        Strings which represent the thermal zone type.
 158        This is given by thermal zone driver as part of registration.
 159        E.g: "acpitz" indicates it's an ACPI thermal device.
 160        In order to keep it consistent with hwmon sys attribute; this should
 161        be a short, lowercase string, not containing spaces nor dashes.
 162        RO, Required
 163
 164temp
 165        Current temperature as reported by thermal zone (sensor).
 166        Unit: millidegree Celsius
 167        RO, Required
 168
 169mode
 170        One of the predefined values in [kernel, user].
 171        This file gives information about the algorithm that is currently
 172        managing the thermal zone. It can be either default kernel based
 173        algorithm or user space application.
 174        kernel  = Thermal management in kernel thermal zone driver.
 175        user    = Preventing kernel thermal zone driver actions upon
 176                  trip points so that user application can take full
 177                  charge of the thermal management.
 178        RW, Optional
 179
 180trip_point_[0-*]_temp
 181        The temperature above which trip point will be fired.
 182        Unit: millidegree Celsius
 183        RO, Optional
 184
 185trip_point_[0-*]_type
 186        Strings which indicate the type of the trip point.
 187        E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 188        thermal zone.
 189        RO, Optional
 190
 191cdev[0-*]
 192        Sysfs link to the thermal cooling device node where the sys I/F
 193        for cooling device throttling control represents.
 194        RO, Optional
 195
 196cdev[0-*]_trip_point
 197        The trip point with which cdev[0-*] is associated in this thermal
 198        zone; -1 means the cooling device is not associated with any trip
 199        point.
 200        RO, Optional
 201
 202passive
 203        Attribute is only present for zones in which the passive cooling
 204        policy is not supported by native thermal driver. Default is zero
 205        and can be set to a temperature (in millidegrees) to enable a
 206        passive trip point for the zone. Activation is done by polling with
 207        an interval of 1 second.
 208        Unit: millidegrees Celsius
 209        Valid values: 0 (disabled) or greater than 1000
 210        RW, Optional
 211
 212*****************************
 213* Cooling device attributes *
 214*****************************
 215
 216type
 217        String which represents the type of device, e.g:
 218        - for generic ACPI: should be "Fan", "Processor" or "LCD"
 219        - for memory controller device on intel_menlow platform:
 220          should be "Memory controller".
 221        RO, Required
 222
 223max_state
 224        The maximum permissible cooling state of this cooling device.
 225        RO, Required
 226
 227cur_state
 228        The current cooling state of this cooling device.
 229        The value can any integer numbers between 0 and max_state:
 230        - cur_state == 0 means no cooling
 231        - cur_state == max_state means the maximum cooling.
 232        RW, Required
 233
 2343. A simple implementation
 235
 236ACPI thermal zone may support multiple trip points like critical, hot,
 237passive, active. If an ACPI thermal zone supports critical, passive,
 238active[0] and active[1] at the same time, it may register itself as a
 239thermal_zone_device (thermal_zone1) with 4 trip points in all.
 240It has one processor and one fan, which are both registered as
 241thermal_cooling_device.
 242
 243If the processor is listed in _PSL method, and the fan is listed in _AL0
 244method, the sys I/F structure will be built like this:
 245
 246/sys/class/thermal:
 247
 248|thermal_zone1:
 249    |---type:                   acpitz
 250    |---temp:                   37000
 251    |---mode:                   kernel
 252    |---trip_point_0_temp:      100000
 253    |---trip_point_0_type:      critical
 254    |---trip_point_1_temp:      80000
 255    |---trip_point_1_type:      passive
 256    |---trip_point_2_temp:      70000
 257    |---trip_point_2_type:      active0
 258    |---trip_point_3_temp:      60000
 259    |---trip_point_3_type:      active1
 260    |---cdev0:                  --->/sys/class/thermal/cooling_device0
 261    |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 262    |---cdev1:                  --->/sys/class/thermal/cooling_device3
 263    |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 264
 265|cooling_device0:
 266    |---type:                   Processor
 267    |---max_state:              8
 268    |---cur_state:              0
 269
 270|cooling_device3:
 271    |---type:                   Fan
 272    |---max_state:              2
 273    |---cur_state:              0
 274
 275/sys/class/hwmon:
 276
 277|hwmon0:
 278    |---name:                   acpitz
 279    |---temp1_input:            37000
 280    |---temp1_crit:             100000
 281
 2824. Event Notification
 283
 284The framework includes a simple notification mechanism, in the form of a
 285netlink event. Netlink socket initialization is done during the _init_
 286of the framework. Drivers which intend to use the notification mechanism
 287just need to call thermal_generate_netlink_event() with two arguments viz
 288(originator, event). Typically the originator will be an integer assigned
 289to a thermal_zone_device when it registers itself with the framework. The
 290event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 291THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 292crosses any of the configured thresholds.
 293
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