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, int mask, void *devdata,
  36                struct thermal_zone_device_ops *ops)
  37
  38    This interface function adds a new thermal zone device (sensor) to
  39    /sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
  40    thermal cooling devices registered at the same time.
  41
  42    name: the thermal zone name.
  43    trips: the total number of trip points this thermal zone supports.
  44    mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
  45    devdata: device private data
  46    ops: thermal zone device call-backs.
  47        .bind: bind the thermal zone device with a thermal cooling device.
  48        .unbind: unbind the thermal zone device with a thermal cooling device.
  49        .get_temp: get the current temperature of the thermal zone.
  50        .get_mode: get the current mode (enabled/disabled) of the thermal zone.
  51            - "enabled" means the kernel thermal management is enabled.
  52            - "disabled" will prevent kernel thermal driver action upon trip points
  53              so that user applications can take charge of thermal management.
  54        .set_mode: set the mode (enabled/disabled) of the thermal zone.
  55        .get_trip_type: get the type of certain trip point.
  56        .get_trip_temp: get the temperature above which the certain trip point
  57                        will be fired.
  58
  591.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  60
  61    This interface function removes the thermal zone device.
  62    It deletes the corresponding entry form /sys/class/thermal folder and
  63    unbind all the thermal cooling devices it uses.
  64
  651.2 thermal cooling device interface
  661.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
  67                void *devdata, struct thermal_cooling_device_ops *)
  68
  69    This interface function adds a new thermal cooling device (fan/processor/...)
  70    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
  71    to all the thermal zone devices register at the same time.
  72    name: the cooling device name.
  73    devdata: device private data.
  74    ops: thermal cooling devices call-backs.
  75        .get_max_state: get the Maximum throttle state of the cooling device.
  76        .get_cur_state: get the Current throttle state of the cooling device.
  77        .set_cur_state: set the Current throttle state of the cooling device.
  78
  791.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  80
  81    This interface function remove the thermal cooling device.
  82    It deletes the corresponding entry form /sys/class/thermal folder and
  83    unbind itself from all the thermal zone devices using it.
  84
  851.3 interface for binding a thermal zone device with a thermal cooling device
  861.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
  87                int trip, struct thermal_cooling_device *cdev);
  88
  89    This interface function bind a thermal cooling device to the certain trip
  90    point of a thermal zone device.
  91    This function is usually called in the thermal zone device .bind callback.
  92    tz: the thermal zone device
  93    cdev: thermal cooling device
  94    trip: indicates which trip point the cooling devices is associated with
  95          in this thermal zone.
  96
  971.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
  98                int trip, struct thermal_cooling_device *cdev);
  99
 100    This interface function unbind a thermal cooling device from the certain
 101    trip point of a thermal zone device. This function is usually called in
 102    the thermal zone device .unbind callback.
 103    tz: the thermal zone device
 104    cdev: thermal cooling device
 105    trip: indicates which trip point the cooling devices is associated with
 106          in this thermal zone.
 107
 1082. sysfs attributes structure
 109
 110RO      read only value
 111RW      read/write value
 112
 113Thermal sysfs attributes will be represented under /sys/class/thermal.
 114Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 115if hwmon is compiled in or built as a module.
 116
 117Thermal zone device sys I/F, created once it's registered:
 118/sys/class/thermal/thermal_zone[0-*]:
 119    |---type:                   Type of the thermal zone
 120    |---temp:                   Current temperature
 121    |---mode:                   Working mode of the thermal zone
 122    |---trip_point_[0-*]_temp:  Trip point temperature
 123    |---trip_point_[0-*]_type:  Trip point type
 124    |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 125
 126Thermal cooling device sys I/F, created once it's registered:
 127/sys/class/thermal/cooling_device[0-*]:
 128    |---type:                   Type of the cooling device(processor/fan/...)
 129    |---max_state:              Maximum cooling state of the cooling device
 130    |---cur_state:              Current cooling state of the cooling device
 131
 132
 133Then next two dynamic attributes are created/removed in pairs. They represent
 134the relationship between a thermal zone and its associated cooling device.
 135They are created/removed for each successful execution of
 136thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 137
 138/sys/class/thermal/thermal_zone[0-*]:
 139    |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 140    |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 141
 142Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 143the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 144of thermal zone device. E.g. the generic thermal driver registers one hwmon
 145class device and build the associated hwmon sysfs I/F for all the registered
 146ACPI thermal zones.
 147
 148/sys/class/hwmon/hwmon[0-*]:
 149    |---name:                   The type of the thermal zone devices
 150    |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 151    |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 152
 153Please read Documentation/hwmon/sysfs-interface for additional information.
 154
 155***************************
 156* Thermal zone attributes *
 157***************************
 158
 159type
 160        Strings which represent the thermal zone type.
 161        This is given by thermal zone driver as part of registration.
 162        E.g: "acpitz" indicates it's an ACPI thermal device.
 163        In order to keep it consistent with hwmon sys attribute; this should
 164        be a short, lowercase string, not containing spaces nor dashes.
 165        RO, Required
 166
 167temp
 168        Current temperature as reported by thermal zone (sensor).
 169        Unit: millidegree Celsius
 170        RO, Required
 171
 172mode
 173        One of the predefined values in [enabled, disabled].
 174        This file gives information about the algorithm that is currently
 175        managing the thermal zone. It can be either default kernel based
 176        algorithm or user space application.
 177        enabled         = enable Kernel Thermal management.
 178        disabled        = Preventing kernel thermal zone driver actions upon
 179                          trip points so that user application can take full
 180                          charge of the thermal management.
 181        RW, Optional
 182
 183trip_point_[0-*]_temp
 184        The temperature above which trip point will be fired.
 185        Unit: millidegree Celsius
 186        RO, Optional
 187
 188trip_point_[0-*]_type
 189        Strings which indicate the type of the trip point.
 190        E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 191        thermal zone.
 192        RO, Optional
 193
 194trip_point_[0-*]_hyst
 195        The hysteresis value for a trip point, represented as an integer
 196        Unit: Celsius
 197        RW, Optional
 198
 199cdev[0-*]
 200        Sysfs link to the thermal cooling device node where the sys I/F
 201        for cooling device throttling control represents.
 202        RO, Optional
 203
 204cdev[0-*]_trip_point
 205        The trip point with which cdev[0-*] is associated in this thermal
 206        zone; -1 means the cooling device is not associated with any trip
 207        point.
 208        RO, Optional
 209
 210passive
 211        Attribute is only present for zones in which the passive cooling
 212        policy is not supported by native thermal driver. Default is zero
 213        and can be set to a temperature (in millidegrees) to enable a
 214        passive trip point for the zone. Activation is done by polling with
 215        an interval of 1 second.
 216        Unit: millidegrees Celsius
 217        Valid values: 0 (disabled) or greater than 1000
 218        RW, Optional
 219
 220*****************************
 221* Cooling device attributes *
 222*****************************
 223
 224type
 225        String which represents the type of device, e.g:
 226        - for generic ACPI: should be "Fan", "Processor" or "LCD"
 227        - for memory controller device on intel_menlow platform:
 228          should be "Memory controller".
 229        RO, Required
 230
 231max_state
 232        The maximum permissible cooling state of this cooling device.
 233        RO, Required
 234
 235cur_state
 236        The current cooling state of this cooling device.
 237        The value can any integer numbers between 0 and max_state:
 238        - cur_state == 0 means no cooling
 239        - cur_state == max_state means the maximum cooling.
 240        RW, Required
 241
 2423. A simple implementation
 243
 244ACPI thermal zone may support multiple trip points like critical, hot,
 245passive, active. If an ACPI thermal zone supports critical, passive,
 246active[0] and active[1] at the same time, it may register itself as a
 247thermal_zone_device (thermal_zone1) with 4 trip points in all.
 248It has one processor and one fan, which are both registered as
 249thermal_cooling_device.
 250
 251If the processor is listed in _PSL method, and the fan is listed in _AL0
 252method, the sys I/F structure will be built like this:
 253
 254/sys/class/thermal:
 255
 256|thermal_zone1:
 257    |---type:                   acpitz
 258    |---temp:                   37000
 259    |---mode:                   enabled
 260    |---trip_point_0_temp:      100000
 261    |---trip_point_0_type:      critical
 262    |---trip_point_1_temp:      80000
 263    |---trip_point_1_type:      passive
 264    |---trip_point_2_temp:      70000
 265    |---trip_point_2_type:      active0
 266    |---trip_point_3_temp:      60000
 267    |---trip_point_3_type:      active1
 268    |---cdev0:                  --->/sys/class/thermal/cooling_device0
 269    |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 270    |---cdev1:                  --->/sys/class/thermal/cooling_device3
 271    |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 272
 273|cooling_device0:
 274    |---type:                   Processor
 275    |---max_state:              8
 276    |---cur_state:              0
 277
 278|cooling_device3:
 279    |---type:                   Fan
 280    |---max_state:              2
 281    |---cur_state:              0
 282
 283/sys/class/hwmon:
 284
 285|hwmon0:
 286    |---name:                   acpitz
 287    |---temp1_input:            37000
 288    |---temp1_crit:             100000
 289
 2904. Event Notification
 291
 292The framework includes a simple notification mechanism, in the form of a
 293netlink event. Netlink socket initialization is done during the _init_
 294of the framework. Drivers which intend to use the notification mechanism
 295just need to call thermal_generate_netlink_event() with two arguments viz
 296(originator, event). Typically the originator will be an integer assigned
 297to a thermal_zone_device when it registers itself with the framework. The
 298event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 299THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 300crosses any of the configured thresholds.
 301
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