Documentation/thermal/sysfs-api.txt

   1 Generic Thermal Sysfs driver How To
   2 ===================================
   3
   4 Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
   5
   6 Updated: 2 January 2008
   7
   8 Copyright (c)  2008 Intel Corporation
   9
  10
  11 0. Introduction
  12
  13 The generic thermal sysfs provides a set of interfaces for thermal zone
  14 devices (sensors) and thermal cooling devices (fan, processor...) to register
  15 with the thermal management solution and to be a part of it.
  16
  17 This how-to focuses on enabling new thermal zone and cooling devices to
  18 participate in thermal management.
  19 This solution is platform independent and any type of thermal zone devices
  20 and cooling devices should be able to make use of the infrastructure.
  21
  22 The main task of the thermal sysfs driver is to expose thermal zone attributes
  23 as well as cooling device attributes to the user space.
  24 An intelligent thermal management application can make decisions based on
  25 inputs from thermal zone attributes (the current temperature and trip point
  26 temperature) and throttle appropriate devices.
  27
  28 [0-*]   denotes any positive number starting from 0
  29 [1-*]   denotes any positive number starting from 1
  30
  31 1. thermal sysfs driver interface functions
  32
  33 1.1 thermal zone device interface
  34 1.1.1 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))
  39
  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.
  43
  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).
  67
  68
  69 1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  70
  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.
  74
  75 1.2 thermal cooling device interface
  76 1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
  77                 void *devdata, struct thermal_cooling_device_ops *)
  78
  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.
  88
  89 1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  90
  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.
  94
  95 1.3 interface for binding a thermal zone device with a thermal cooling device
  96 1.3.1 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);
  99
 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.
 113
 114 1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
 115                 int trip, struct thermal_cooling_device *cdev);
 116
 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.
 124
 125 1.4 Thermal Zone Parameters
 126 1.4.1 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.
 139 1.4.2 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     .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
 146                is required. when no_hwmon == false, a hwmon sysfs interface
 147                will be created. when no_hwmon == true, nothing will be done.
 148                In case the thermal_zone_params is NULL, the hwmon interface
 149                will be created (for backward compatibility).
 150     .num_tbps: Number of thermal_bind_params entries for this zone
 151     .tbp: thermal_bind_params entries
 152
 153 2. sysfs attributes structure
 154
 155 RO      read only value
 156 RW      read/write value
 157
 158 Thermal sysfs attributes will be represented under /sys/class/thermal.
 159 Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 160 if hwmon is compiled in or built as a module.
 161
 162 Thermal zone device sys I/F, created once it's registered:
 163 /sys/class/thermal/thermal_zone[0-*]:
 164     |---type:                   Type of the thermal zone
 165     |---temp:                   Current temperature
 166     |---mode:                   Working mode of the thermal zone
 167     |---policy:                 Thermal governor used for this zone
 168     |---trip_point_[0-*]_temp:  Trip point temperature
 169     |---trip_point_[0-*]_type:  Trip point type
 170     |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 171     |---emul_temp:              Emulated temperature set node
 172
 173 Thermal cooling device sys I/F, created once it's registered:
 174 /sys/class/thermal/cooling_device[0-*]:
 175     |---type:                   Type of the cooling device(processor/fan/...)
 176     |---max_state:              Maximum cooling state of the cooling device
 177     |---cur_state:              Current cooling state of the cooling device
 178
 179
 180 Then next two dynamic attributes are created/removed in pairs. They represent
 181 the relationship between a thermal zone and its associated cooling device.
 182 They are created/removed for each successful execution of
 183 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 184
 185 /sys/class/thermal/thermal_zone[0-*]:
 186     |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 187     |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 188
 189 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 190 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 191 of thermal zone device. E.g. the generic thermal driver registers one hwmon
 192 class device and build the associated hwmon sysfs I/F for all the registered
 193 ACPI thermal zones.
 194
 195 /sys/class/hwmon/hwmon[0-*]:
 196     |---name:                   The type of the thermal zone devices
 197     |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 198     |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 199
 200 Please read Documentation/hwmon/sysfs-interface for additional information.
 201
 202 ***************************
 203 * Thermal zone attributes *
 204 ***************************
 205
 206 type
 207         Strings which represent the thermal zone type.
 208         This is given by thermal zone driver as part of registration.
 209         E.g: "acpitz" indicates it's an ACPI thermal device.
 210         In order to keep it consistent with hwmon sys attribute; this should
 211         be a short, lowercase string, not containing spaces nor dashes.
 212         RO, Required
 213
 214 temp
 215         Current temperature as reported by thermal zone (sensor).
 216         Unit: millidegree Celsius
 217         RO, Required
 218
 219 mode
 220         One of the predefined values in [enabled, disabled].
 221         This file gives information about the algorithm that is currently
 222         managing the thermal zone. It can be either default kernel based
 223         algorithm or user space application.
 224         enabled         = enable Kernel Thermal management.
 225         disabled        = Preventing kernel thermal zone driver actions upon
 226                           trip points so that user application can take full
 227                           charge of the thermal management.
 228         RW, Optional
 229
 230 policy
 231         One of the various thermal governors used for a particular zone.
 232         RW, Required
 233
 234 trip_point_[0-*]_temp
 235         The temperature above which trip point will be fired.
 236         Unit: millidegree Celsius
 237         RO, Optional
 238
 239 trip_point_[0-*]_type
 240         Strings which indicate the type of the trip point.
 241         E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 242         thermal zone.
 243         RO, Optional
 244
 245 trip_point_[0-*]_hyst
 246         The hysteresis value for a trip point, represented as an integer
 247         Unit: Celsius
 248         RW, Optional
 249
 250 cdev[0-*]
 251         Sysfs link to the thermal cooling device node where the sys I/F
 252         for cooling device throttling control represents.
 253         RO, Optional
 254
 255 cdev[0-*]_trip_point
 256         The trip point with which cdev[0-*] is associated in this thermal
 257         zone; -1 means the cooling device is not associated with any trip
 258         point.
 259         RO, Optional
 260
 261 passive
 262         Attribute is only present for zones in which the passive cooling
 263         policy is not supported by native thermal driver. Default is zero
 264         and can be set to a temperature (in millidegrees) to enable a
 265         passive trip point for the zone. Activation is done by polling with
 266         an interval of 1 second.
 267         Unit: millidegrees Celsius
 268         Valid values: 0 (disabled) or greater than 1000
 269         RW, Optional
 270
 271 emul_temp
 272         Interface to set the emulated temperature method in thermal zone
 273         (sensor). After setting this temperature, the thermal zone may pass
 274         this temperature to platform emulation function if registered or
 275         cache it locally. This is useful in debugging different temperature
 276         threshold and its associated cooling action. This is write only node
 277         and writing 0 on this node should disable emulation.
 278         Unit: millidegree Celsius
 279         WO, Optional
 280
 281           WARNING: Be careful while enabling this option on production systems,
 282           because userland can easily disable the thermal policy by simply
 283           flooding this sysfs node with low temperature values.
 284
 285 *****************************
 286 * Cooling device attributes *
 287 *****************************
 288
 289 type
 290         String which represents the type of device, e.g:
 291         - for generic ACPI: should be "Fan", "Processor" or "LCD"
 292         - for memory controller device on intel_menlow platform:
 293           should be "Memory controller".
 294         RO, Required
 295
 296 max_state
 297         The maximum permissible cooling state of this cooling device.
 298         RO, Required
 299
 300 cur_state
 301         The current cooling state of this cooling device.
 302         The value can any integer numbers between 0 and max_state:
 303         - cur_state == 0 means no cooling
 304         - cur_state == max_state means the maximum cooling.
 305         RW, Required
 306
 307 3. A simple implementation
 308
 309 ACPI thermal zone may support multiple trip points like critical, hot,
 310 passive, active. If an ACPI thermal zone supports critical, passive,
 311 active[0] and active[1] at the same time, it may register itself as a
 312 thermal_zone_device (thermal_zone1) with 4 trip points in all.
 313 It has one processor and one fan, which are both registered as
 314 thermal_cooling_device.
 315
 316 If the processor is listed in _PSL method, and the fan is listed in _AL0
 317 method, the sys I/F structure will be built like this:
 318
 319 /sys/class/thermal:
 320
 321 |thermal_zone1:
 322     |---type:                   acpitz
 323     |---temp:                   37000
 324     |---mode:                   enabled
 325     |---policy:                 step_wise
 326     |---trip_point_0_temp:      100000
 327     |---trip_point_0_type:      critical
 328     |---trip_point_1_temp:      80000
 329     |---trip_point_1_type:      passive
 330     |---trip_point_2_temp:      70000
 331     |---trip_point_2_type:      active0
 332     |---trip_point_3_temp:      60000
 333     |---trip_point_3_type:      active1
 334     |---cdev0:                  --->/sys/class/thermal/cooling_device0
 335     |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 336     |---cdev1:                  --->/sys/class/thermal/cooling_device3
 337     |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 338
 339 |cooling_device0:
 340     |---type:                   Processor
 341     |---max_state:              8
 342     |---cur_state:              0
 343
 344 |cooling_device3:
 345     |---type:                   Fan
 346     |---max_state:              2
 347     |---cur_state:              0
 348
 349 /sys/class/hwmon:
 350
 351 |hwmon0:
 352     |---name:                   acpitz
 353     |---temp1_input:            37000
 354     |---temp1_crit:             100000
 355
 356 4. Event Notification
 357
 358 The framework includes a simple notification mechanism, in the form of a
 359 netlink event. Netlink socket initialization is done during the _init_
 360 of the framework. Drivers which intend to use the notification mechanism
 361 just need to call thermal_generate_netlink_event() with two arguments viz
 362 (originator, event). The originator is a pointer to struct thermal_zone_device
 363 from where the event has been originated. An integer which represents the
 364 thermal zone device will be used in the message to identify the zone. The
 365 event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 366 THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 367 crosses any of the configured thresholds.
 368
 369 5. Export Symbol APIs:
 370
 371 5.1: get_tz_trend:
 372 This function returns the trend of a thermal zone, i.e the rate of change
 373 of temperature of the thermal zone. Ideally, the thermal sensor drivers
 374 are supposed to implement the callback. If they don't, the thermal
 375 framework calculated the trend by comparing the previous and the current
 376 temperature values.
 377
 378 5.2:get_thermal_instance:
 379 This function returns the thermal_instance corresponding to a given
 380 {thermal_zone, cooling_device, trip_point} combination. Returns NULL
 381 if such an instance does not exist.
 382
 383 5.3:thermal_notify_framework:
 384 This function handles the trip events from sensor drivers. It starts
 385 throttling the cooling devices according to the policy configured.
 386 For CRITICAL and HOT trip points, this notifies the respective drivers,
 387 and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
 388 The throttling policy is based on the configured platform data; if no
 389 platform data is provided, this uses the step_wise throttling policy.
 390
 391 5.4:thermal_cdev_update:
 392 This function serves as an arbitrator to set the state of a cooling
 393 device. It sets the cooling device to the deepest cooling state if
 394 possible.