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 devices (sensors)
  14and thermal cooling devices (fan, processor...) to register with the thermal management
  15solution and to be a part of it.
  17This how-to focuses on enabling new thermal zone and cooling devices to participate
  18in thermal management.
  19This solution is platform independent and any type of thermal zone devices and
  20cooling devices should be able to make use of the infrastructure.
  22The main task of the thermal sysfs driver is to expose thermal zone attributes as well
  23as cooling device attributes to the user space.
  24An intelligent thermal management application can make decisions based on inputs
  25from thermal zone attributes (the current temperature and trip point temperature)
  26and 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 *name, int trips,
  35                                void *devdata, struct thermal_zone_device_ops *ops)
  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.
  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.
  571.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  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.
  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 *)
  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.
  771.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  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.
  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);
  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.
  951.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
  96                                int trip, struct thermal_cooling_device *cdev);
  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.
 1062. sysfs attributes structure
 108RO      read only value
 109RW      read/write value
 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.
 115Thermal zone device sys I/F, created once it's registered:
 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
 123Thermal cooling device sys I/F, created once it's registered:
 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
 130These two dynamic attributes are created/removed in pairs.
 131They represent the relationship between a thermal zone and its associated cooling device.
 132They are created/removed for each
 133thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful execution.
 136        |-----cdev[0-*]:                The [0-*]th cooling device in the current thermal zone
 137        |-----cdev[0-*]_trip_point:     Trip point that cdev[0-*] is associated with
 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_ of
 141thermal zone device. E.g. the generic thermal driver registers one hwmon class device
 142and build the associated hwmon sysfs I/F for all the registered ACPI thermal zones.
 144        |-----name:                     The type of the thermal zone devices.
 145        |-----temp[1-*]_input:          The current temperature of thermal zone [1-*].
 146        |-----temp[1-*]_critical:       The critical trip point of thermal zone [1-*].
 147Please read Documentation/hwmon/sysfs-interface for additional information.
 150* Thermal zone attributes *
 153type                            Strings which represent the thermal zone type.
 154                                This is given by thermal zone driver as part of registration.
 155                                Eg: "acpitz" indicates it's an ACPI thermal device.
 156                                In order to keep it consistent with hwmon sys attribute,
 157                                this should be a short, lowercase string,
 158                                not containing spaces nor dashes.
 159                                RO
 160                                Required
 162temp                            Current temperature as reported by thermal zone (sensor)
 163                                Unit: millidegree Celsius
 164                                RO
 165                                Required
 167mode                            One of the predefined values in [kernel, user]
 168                                This file gives information about the algorithm
 169                                that is currently managing the thermal zone.
 170                                It can be either default kernel based algorithm
 171                                or user space application.
 172                                RW
 173                                Optional
 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.
 179trip_point_[0-*]_temp           The temperature above which trip point will be fired
 180                                Unit: millidegree Celsius
 181                                RO
 182                                Optional
 184trip_point_[0-*]_type           Strings which indicate the type of the trip point
 185                                E.g. it can be one of critical, hot, passive,
 186                                    active[0-*] for ACPI thermal zone.
 187                                RO
 188                                Optional
 190cdev[0-*]                       Sysfs link to the thermal cooling device node where the sys I/F
 191                                for cooling device throttling control represents.
 192                                RO
 193                                Optional
 195cdev[0-*]_trip_point            The trip point with which cdev[0-*] is associated in this thermal zone
 196                                -1 means the cooling device is not associated with any trip point.
 197                                RO
 198                                Optional
 201* Cooling device  attributes *
 204type                            String which represents the type of device
 205                                eg: For generic ACPI: this should be "Fan",
 206                                "Processor" or "LCD"
 207                                eg. For memory controller device on intel_menlow platform:
 208                                this should be "Memory controller"
 209                                RO
 210                                Required
 212max_state                       The maximum permissible cooling state of this cooling device.
 213                                RO
 214                                Required
 216cur_state                       The current cooling state of this cooling device.
 217                                the value can any integer numbers between 0 and max_state,
 218                                cur_state == 0 means no cooling
 219                                cur_state == max_state means the maximum cooling.
 220                                RW
 221                                Required
 2233. A simple implementation
 225ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
 226If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
 227it may register itself as a thermal_zone_device (thermal_zone1) with 4 trip points in all.
 228It has one processor and one fan, which are both registered as thermal_cooling_device.
 229If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
 230the sys I/F structure will be built like this:
 235        |-----type:                     acpitz
 236        |-----temp:                     37000
 237        |-----mode:                     kernel
 238        |-----trip_point_0_temp:        100000
 239        |-----trip_point_0_type:        critical
 240        |-----trip_point_1_temp:        80000
 241        |-----trip_point_1_type:        passive
 242        |-----trip_point_2_temp:        70000
 243        |-----trip_point_2_type:        active0
 244        |-----trip_point_3_temp:        60000
 245        |-----trip_point_3_type:        active1
 246        |-----cdev0:                    --->/sys/class/thermal/cooling_device0
 247        |-----cdev0_trip_point:         1       /* cdev0 can be used for passive */
 248        |-----cdev1:                    --->/sys/class/thermal/cooling_device3
 249        |-----cdev1_trip_point:         2       /* cdev1 can be used for active[0]*/
 252        |-----type:                     Processor
 253        |-----max_state:                8
 254        |-----cur_state:                0
 257        |-----type:                     Fan
 258        |-----max_state:                2
 259        |-----cur_state:                0
 264        |-----name:                     acpitz
 265        |-----temp1_input:              37000
 266        |-----temp1_crit:               100000