1Generic Thermal Sysfs driver How To
   4Written by Sujith Thomas <>, Zhang Rui <>
   6Updated: 2 January 2008
   8Copyright (c)  2008 Intel Corporation
  110. Introduction
  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.
  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.
  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.
  28[0-*]   denotes any positive number starting from 0
  29[1-*]   denotes any positive number starting from 1
  311. thermal sysfs driver interface functions
  331.1 thermal zone device interface
  341.1.1 struct thermal_zone_device *thermal_zone_device_register(char *type,
  35                int trips, int mask, void *devdata,
  36                struct thermal_zone_device_ops *ops,
  37                const struct thermal_zone_params *tzp,
  38                int passive_delay, int polling_delay))
  40    This interface function adds a new thermal zone device (sensor) to
  41    /sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
  42    thermal cooling devices registered at the same time.
  44    type: the thermal zone type.
  45    trips: the total number of trip points this thermal zone supports.
  46    mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
  47    devdata: device private data
  48    ops: thermal zone device call-backs.
  49        .bind: bind the thermal zone device with a thermal cooling device.
  50        .unbind: unbind the thermal zone device with a thermal cooling device.
  51        .get_temp: get the current temperature of the thermal zone.
  52        .get_mode: get the current mode (enabled/disabled) of the thermal zone.
  53            - "enabled" means the kernel thermal management is enabled.
  54            - "disabled" will prevent kernel thermal driver action upon trip points
  55              so that user applications can take charge of thermal management.
  56        .set_mode: set the mode (enabled/disabled) of the thermal zone.
  57        .get_trip_type: get the type of certain trip point.
  58        .get_trip_temp: get the temperature above which the certain trip point
  59                        will be fired.
  60        .set_emul_temp: set the emulation temperature which helps in debugging
  61                        different threshold temperature points.
  62    tzp: thermal zone platform parameters.
  63    passive_delay: number of milliseconds to wait between polls when
  64        performing passive cooling.
  65    polling_delay: number of milliseconds to wait between polls when checking
  66        whether trip points have been crossed (0 for interrupt driven systems).
  691.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  71    This interface function removes the thermal zone device.
  72    It deletes the corresponding entry form /sys/class/thermal folder and
  73    unbind all the thermal cooling devices it uses.
  751.2 thermal cooling device interface
  761.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
  77                void *devdata, struct thermal_cooling_device_ops *)
  79    This interface function adds a new thermal cooling device (fan/processor/...)
  80    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
  81    to all the thermal zone devices register at the same time.
  82    name: the cooling device name.
  83    devdata: device private data.
  84    ops: thermal cooling devices call-backs.
  85        .get_max_state: get the Maximum throttle state of the cooling device.
  86        .get_cur_state: get the Current throttle state of the cooling device.
  87        .set_cur_state: set the Current throttle state of the cooling device.
  891.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  91    This interface function remove the thermal cooling device.
  92    It deletes the corresponding entry form /sys/class/thermal folder and
  93    unbind itself from all the thermal zone devices using it.
  951.3 interface for binding a thermal zone device with a thermal cooling device
  961.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
  97        int trip, struct thermal_cooling_device *cdev,
  98        unsigned long upper, unsigned long lower);
 100    This interface function bind a thermal cooling device to the certain trip
 101    point of a thermal zone device.
 102    This function is usually called in the thermal zone device .bind 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    upper:the Maximum cooling state for this trip point.
 108          THERMAL_NO_LIMIT means no upper limit,
 109          and the cooling device can be in max_state.
 110    lower:the Minimum cooling state can be used for this trip point.
 111          THERMAL_NO_LIMIT means no lower limit,
 112          and the cooling device can be in cooling state 0.
 1141.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
 115                int trip, struct thermal_cooling_device *cdev);
 117    This interface function unbind a thermal cooling device from the certain
 118    trip point of a thermal zone device. This function is usually called in
 119    the thermal zone device .unbind callback.
 120    tz: the thermal zone device
 121    cdev: thermal cooling device
 122    trip: indicates which trip point the cooling devices is associated with
 123          in this thermal zone.
 1251.4 Thermal Zone Parameters
 1261.4.1 struct thermal_bind_params
 127    This structure defines the following parameters that are used to bind
 128    a zone with a cooling device for a particular trip point.
 129    .cdev: The cooling device pointer
 130    .weight: The 'influence' of a particular cooling device on this zone.
 131             This is on a percentage scale. The sum of all these weights
 132             (for a particular zone) cannot exceed 100.
 133    .trip_mask:This is a bit mask that gives the binding relation between
 134               this thermal zone and cdev, for a particular trip point.
 135               If nth bit is set, then the cdev and thermal zone are bound
 136               for trip point n.
 137    .match: This call back returns success(0) if the 'tz and cdev' need to
 138            be bound, as per platform data.
 1391.4.2 struct thermal_zone_params
 140    This structure defines the platform level parameters for a thermal zone.
 141    This data, for each thermal zone should come from the platform layer.
 142    This is an optional feature where some platforms can choose not to
 143    provide this data.
 144    .governor_name: Name of the thermal governor used for this zone
 145    .num_tbps: Number of thermal_bind_params entries for this zone
 146    .tbp: thermal_bind_params entries
 1482. sysfs attributes structure
 150RO      read only value
 151RW      read/write value
 153Thermal sysfs attributes will be represented under /sys/class/thermal.
 154Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 155if hwmon is compiled in or built as a module.
 157Thermal zone device sys I/F, created once it's registered:
 159    |---type:                   Type of the thermal zone
 160    |---temp:                   Current temperature
 161    |---mode:                   Working mode of the thermal zone
 162    |---policy:                 Thermal governor used for this zone
 163    |---trip_point_[0-*]_temp:  Trip point temperature
 164    |---trip_point_[0-*]_type:  Trip point type
 165    |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 166    |---emul_temp:              Emulated temperature set node
 168Thermal cooling device sys I/F, created once it's registered:
 170    |---type:                   Type of the cooling device(processor/fan/...)
 171    |---max_state:              Maximum cooling state of the cooling device
 172    |---cur_state:              Current cooling state of the cooling device
 175Then next two dynamic attributes are created/removed in pairs. They represent
 176the relationship between a thermal zone and its associated cooling device.
 177They are created/removed for each successful execution of
 181    |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 182    |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 184Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 185the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 186of thermal zone device. E.g. the generic thermal driver registers one hwmon
 187class device and build the associated hwmon sysfs I/F for all the registered
 188ACPI thermal zones.
 191    |---name:                   The type of the thermal zone devices
 192    |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 193    |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 195Please read Documentation/hwmon/sysfs-interface for additional information.
 198* Thermal zone attributes *
 202        Strings which represent the thermal zone type.
 203        This is given by thermal zone driver as part of registration.
 204        E.g: "acpitz" indicates it's an ACPI thermal device.
 205        In order to keep it consistent with hwmon sys attribute; this should
 206        be a short, lowercase string, not containing spaces nor dashes.
 207        RO, Required
 210        Current temperature as reported by thermal zone (sensor).
 211        Unit: millidegree Celsius
 212        RO, Required
 215        One of the predefined values in [enabled, disabled].
 216        This file gives information about the algorithm that is currently
 217        managing the thermal zone. It can be either default kernel based
 218        algorithm or user space application.
 219        enabled         = enable Kernel Thermal management.
 220        disabled        = Preventing kernel thermal zone driver actions upon
 221                          trip points so that user application can take full
 222                          charge of the thermal management.
 223        RW, Optional
 226        One of the various thermal governors used for a particular zone.
 227        RW, Required
 230        The temperature above which trip point will be fired.
 231        Unit: millidegree Celsius
 232        RO, Optional
 235        Strings which indicate the type of the trip point.
 236        E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 237        thermal zone.
 238        RO, Optional
 241        The hysteresis value for a trip point, represented as an integer
 242        Unit: Celsius
 243        RW, Optional
 246        Sysfs link to the thermal cooling device node where the sys I/F
 247        for cooling device throttling control represents.
 248        RO, Optional
 251        The trip point with which cdev[0-*] is associated in this thermal
 252        zone; -1 means the cooling device is not associated with any trip
 253        point.
 254        RO, Optional
 257        Attribute is only present for zones in which the passive cooling
 258        policy is not supported by native thermal driver. Default is zero
 259        and can be set to a temperature (in millidegrees) to enable a
 260        passive trip point for the zone. Activation is done by polling with
 261        an interval of 1 second.
 262        Unit: millidegrees Celsius
 263        Valid values: 0 (disabled) or greater than 1000
 264        RW, Optional
 267        Interface to set the emulated temperature method in thermal zone
 268        (sensor). After setting this temperature, the thermal zone may pass
 269        this temperature to platform emulation function if registered or
 270        cache it locally. This is useful in debugging different temperature
 271        threshold and its associated cooling action. This is write only node
 272        and writing 0 on this node should disable emulation.
 273        Unit: millidegree Celsius
 274        WO, Optional
 276          WARNING: Be careful while enabling this option on production systems,
 277          because userland can easily disable the thermal policy by simply
 278          flooding this sysfs node with low temperature values.
 281* Cooling device attributes *
 285        String which represents the type of device, e.g:
 286        - for generic ACPI: should be "Fan", "Processor" or "LCD"
 287        - for memory controller device on intel_menlow platform:
 288          should be "Memory controller".
 289        RO, Required
 292        The maximum permissible cooling state of this cooling device.
 293        RO, Required
 296        The current cooling state of this cooling device.
 297        The value can any integer numbers between 0 and max_state:
 298        - cur_state == 0 means no cooling
 299        - cur_state == max_state means the maximum cooling.
 300        RW, Required
 3023. A simple implementation
 304ACPI thermal zone may support multiple trip points like critical, hot,
 305passive, active. If an ACPI thermal zone supports critical, passive,
 306active[0] and active[1] at the same time, it may register itself as a
 307thermal_zone_device (thermal_zone1) with 4 trip points in all.
 308It has one processor and one fan, which are both registered as
 311If the processor is listed in _PSL method, and the fan is listed in _AL0
 312method, the sys I/F structure will be built like this:
 317    |---type:                   acpitz
 318    |---temp:                   37000
 319    |---mode:                   enabled
 320    |---policy:                 step_wise
 321    |---trip_point_0_temp:      100000
 322    |---trip_point_0_type:      critical
 323    |---trip_point_1_temp:      80000
 324    |---trip_point_1_type:      passive
 325    |---trip_point_2_temp:      70000
 326    |---trip_point_2_type:      active0
 327    |---trip_point_3_temp:      60000
 328    |---trip_point_3_type:      active1
 329    |---cdev0:                  --->/sys/class/thermal/cooling_device0
 330    |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 331    |---cdev1:                  --->/sys/class/thermal/cooling_device3
 332    |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 335    |---type:                   Processor
 336    |---max_state:              8
 337    |---cur_state:              0
 340    |---type:                   Fan
 341    |---max_state:              2
 342    |---cur_state:              0
 347    |---name:                   acpitz
 348    |---temp1_input:            37000
 349    |---temp1_crit:             100000
 3514. Event Notification
 353The framework includes a simple notification mechanism, in the form of a
 354netlink event. Netlink socket initialization is done during the _init_
 355of the framework. Drivers which intend to use the notification mechanism
 356just need to call thermal_generate_netlink_event() with two arguments viz
 357(originator, event). The originator is a pointer to struct thermal_zone_device
 358from where the event has been originated. An integer which represents the
 359thermal zone device will be used in the message to identify the zone. The
 360event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 361THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 362crosses any of the configured thresholds.
 3645. Export Symbol APIs:
 3665.1: get_tz_trend:
 367This function returns the trend of a thermal zone, i.e the rate of change
 368of temperature of the thermal zone. Ideally, the thermal sensor drivers
 369are supposed to implement the callback. If they don't, the thermal
 370framework calculated the trend by comparing the previous and the current
 371temperature values.
 374This function returns the thermal_instance corresponding to a given
 375{thermal_zone, cooling_device, trip_point} combination. Returns NULL
 376if such an instance does not exist.
 379This function handles the trip events from sensor drivers. It starts
 380throttling the cooling devices according to the policy configured.
 381For CRITICAL and HOT trip points, this notifies the respective drivers,
 382and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
 383The throttling policy is based on the configured platform data; if no
 384platform data is provided, this uses the step_wise throttling policy.
 387This function serves as an arbitrator to set the state of a cooling
 388device. It sets the cooling device to the deepest cooling state if
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