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        unsigned long upper, unsigned long lower);
  89
  90    This interface function bind a thermal cooling device to the certain trip
  91    point of a thermal zone device.
  92    This function is usually called in the thermal zone device .bind callback.
  93    tz: the thermal zone device
  94    cdev: thermal cooling device
  95    trip: indicates which trip point the cooling devices is associated with
  96          in this thermal zone.
  97    upper:the Maximum cooling state for this trip point.
  98          THERMAL_NO_LIMIT means no upper limit,
  99          and the cooling device can be in max_state.
 100    lower:the Minimum cooling state can be used for this trip point.
 101          THERMAL_NO_LIMIT means no lower limit,
 102          and the cooling device can be in cooling state 0.
 103
 1041.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
 105                int trip, struct thermal_cooling_device *cdev);
 106
 107    This interface function unbind a thermal cooling device from the certain
 108    trip point of a thermal zone device. This function is usually called in
 109    the thermal zone device .unbind callback.
 110    tz: the thermal zone device
 111    cdev: thermal cooling device
 112    trip: indicates which trip point the cooling devices is associated with
 113          in this thermal zone.
 114
 1152. sysfs attributes structure
 116
 117RO      read only value
 118RW      read/write value
 119
 120Thermal sysfs attributes will be represented under /sys/class/thermal.
 121Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 122if hwmon is compiled in or built as a module.
 123
 124Thermal zone device sys I/F, created once it's registered:
 125/sys/class/thermal/thermal_zone[0-*]:
 126    |---type:                   Type of the thermal zone
 127    |---temp:                   Current temperature
 128    |---mode:                   Working mode of the thermal zone
 129    |---trip_point_[0-*]_temp:  Trip point temperature
 130    |---trip_point_[0-*]_type:  Trip point type
 131    |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 132
 133Thermal cooling device sys I/F, created once it's registered:
 134/sys/class/thermal/cooling_device[0-*]:
 135    |---type:                   Type of the cooling device(processor/fan/...)
 136    |---max_state:              Maximum cooling state of the cooling device
 137    |---cur_state:              Current cooling state of the cooling device
 138
 139
 140Then next two dynamic attributes are created/removed in pairs. They represent
 141the relationship between a thermal zone and its associated cooling device.
 142They are created/removed for each successful execution of
 143thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 144
 145/sys/class/thermal/thermal_zone[0-*]:
 146    |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 147    |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 148
 149Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 150the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 151of thermal zone device. E.g. the generic thermal driver registers one hwmon
 152class device and build the associated hwmon sysfs I/F for all the registered
 153ACPI thermal zones.
 154
 155/sys/class/hwmon/hwmon[0-*]:
 156    |---name:                   The type of the thermal zone devices
 157    |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 158    |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 159
 160Please read Documentation/hwmon/sysfs-interface for additional information.
 161
 162***************************
 163* Thermal zone attributes *
 164***************************
 165
 166type
 167        Strings which represent the thermal zone type.
 168        This is given by thermal zone driver as part of registration.
 169        E.g: "acpitz" indicates it's an ACPI thermal device.
 170        In order to keep it consistent with hwmon sys attribute; this should
 171        be a short, lowercase string, not containing spaces nor dashes.
 172        RO, Required
 173
 174temp
 175        Current temperature as reported by thermal zone (sensor).
 176        Unit: millidegree Celsius
 177        RO, Required
 178
 179mode
 180        One of the predefined values in [enabled, disabled].
 181        This file gives information about the algorithm that is currently
 182        managing the thermal zone. It can be either default kernel based
 183        algorithm or user space application.
 184        enabled         = enable Kernel Thermal management.
 185        disabled        = Preventing kernel thermal zone driver actions upon
 186                          trip points so that user application can take full
 187                          charge of the thermal management.
 188        RW, Optional
 189
 190trip_point_[0-*]_temp
 191        The temperature above which trip point will be fired.
 192        Unit: millidegree Celsius
 193        RO, Optional
 194
 195trip_point_[0-*]_type
 196        Strings which indicate the type of the trip point.
 197        E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 198        thermal zone.
 199        RO, Optional
 200
 201trip_point_[0-*]_hyst
 202        The hysteresis value for a trip point, represented as an integer
 203        Unit: Celsius
 204        RW, Optional
 205
 206cdev[0-*]
 207        Sysfs link to the thermal cooling device node where the sys I/F
 208        for cooling device throttling control represents.
 209        RO, Optional
 210
 211cdev[0-*]_trip_point
 212        The trip point with which cdev[0-*] is associated in this thermal
 213        zone; -1 means the cooling device is not associated with any trip
 214        point.
 215        RO, Optional
 216
 217passive
 218        Attribute is only present for zones in which the passive cooling
 219        policy is not supported by native thermal driver. Default is zero
 220        and can be set to a temperature (in millidegrees) to enable a
 221        passive trip point for the zone. Activation is done by polling with
 222        an interval of 1 second.
 223        Unit: millidegrees Celsius
 224        Valid values: 0 (disabled) or greater than 1000
 225        RW, Optional
 226
 227*****************************
 228* Cooling device attributes *
 229*****************************
 230
 231type
 232        String which represents the type of device, e.g:
 233        - for generic ACPI: should be "Fan", "Processor" or "LCD"
 234        - for memory controller device on intel_menlow platform:
 235          should be "Memory controller".
 236        RO, Required
 237
 238max_state
 239        The maximum permissible cooling state of this cooling device.
 240        RO, Required
 241
 242cur_state
 243        The current cooling state of this cooling device.
 244        The value can any integer numbers between 0 and max_state:
 245        - cur_state == 0 means no cooling
 246        - cur_state == max_state means the maximum cooling.
 247        RW, Required
 248
 2493. A simple implementation
 250
 251ACPI thermal zone may support multiple trip points like critical, hot,
 252passive, active. If an ACPI thermal zone supports critical, passive,
 253active[0] and active[1] at the same time, it may register itself as a
 254thermal_zone_device (thermal_zone1) with 4 trip points in all.
 255It has one processor and one fan, which are both registered as
 256thermal_cooling_device.
 257
 258If the processor is listed in _PSL method, and the fan is listed in _AL0
 259method, the sys I/F structure will be built like this:
 260
 261/sys/class/thermal:
 262
 263|thermal_zone1:
 264    |---type:                   acpitz
 265    |---temp:                   37000
 266    |---mode:                   enabled
 267    |---trip_point_0_temp:      100000
 268    |---trip_point_0_type:      critical
 269    |---trip_point_1_temp:      80000
 270    |---trip_point_1_type:      passive
 271    |---trip_point_2_temp:      70000
 272    |---trip_point_2_type:      active0
 273    |---trip_point_3_temp:      60000
 274    |---trip_point_3_type:      active1
 275    |---cdev0:                  --->/sys/class/thermal/cooling_device0
 276    |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 277    |---cdev1:                  --->/sys/class/thermal/cooling_device3
 278    |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 279
 280|cooling_device0:
 281    |---type:                   Processor
 282    |---max_state:              8
 283    |---cur_state:              0
 284
 285|cooling_device3:
 286    |---type:                   Fan
 287    |---max_state:              2
 288    |---cur_state:              0
 289
 290/sys/class/hwmon:
 291
 292|hwmon0:
 293    |---name:                   acpitz
 294    |---temp1_input:            37000
 295    |---temp1_crit:             100000
 296
 2974. Event Notification
 298
 299The framework includes a simple notification mechanism, in the form of a
 300netlink event. Netlink socket initialization is done during the _init_
 301of the framework. Drivers which intend to use the notification mechanism
 302just need to call thermal_generate_netlink_event() with two arguments viz
 303(originator, event). Typically the originator will be an integer assigned
 304to a thermal_zone_device when it registers itself with the framework. The
 305event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 306THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 307crosses any of the configured thresholds.
 308
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