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 1.1.3 struct thermal_zone_device *thermal_zone_of_sensor_register(
  76                 struct device *dev, int sensor_id, void *data,
  77                 const struct thermal_zone_of_device_ops *ops)
  78
  79         This interface adds a new sensor to a DT thermal zone.
  80         This function will search the list of thermal zones described in
  81         device tree and look for the zone that refer to the sensor device
  82         pointed by dev->of_node as temperature providers. For the zone
  83         pointing to the sensor node, the sensor will be added to the DT
  84         thermal zone device.
  85
  86         The parameters for this interface are:
  87         dev:            Device node of sensor containing valid node pointer in
  88                         dev->of_node.
  89         sensor_id:      a sensor identifier, in case the sensor IP has more
  90                         than one sensors
  91         data:           a private pointer (owned by the caller) that will be
  92                         passed back, when a temperature reading is needed.
  93         ops:            struct thermal_zone_of_device_ops *.
  94
  95                         get_temp:       a pointer to a function that reads the
  96                                         sensor temperature. This is mandatory
  97                                         callback provided by sensor driver.
  98                         get_trend:      a pointer to a function that reads the
  99                                         sensor temperature trend.
 100                         set_emul_temp:  a pointer to a function that sets
 101                                         sensor emulated temperature.
 102         The thermal zone temperature is provided by the get_temp() function
 103         pointer of thermal_zone_of_device_ops. When called, it will
 104         have the private pointer @data back.
 105
 106         It returns error pointer if fails otherwise valid thermal zone device
 107         handle. Caller should check the return handle with IS_ERR() for finding
 108         whether success or not.
 109
 110 1.1.4 void thermal_zone_of_sensor_unregister(struct device *dev,
 111                 struct thermal_zone_device *tzd)
 112
 113         This interface unregisters a sensor from a DT thermal zone which was
 114         successfully added by interface thermal_zone_of_sensor_register().
 115         This function removes the sensor callbacks and private data from the
 116         thermal zone device registered with thermal_zone_of_sensor_register()
 117         interface. It will also silent the zone by remove the .get_temp() and
 118         get_trend() thermal zone device callbacks.
 119
 120 1.2 thermal cooling device interface
 121 1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
 122                 void *devdata, struct thermal_cooling_device_ops *)
 123
 124     This interface function adds a new thermal cooling device (fan/processor/...)
 125     to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
 126     to all the thermal zone devices register at the same time.
 127     name: the cooling device name.
 128     devdata: device private data.
 129     ops: thermal cooling devices call-backs.
 130         .get_max_state: get the Maximum throttle state of the cooling device.
 131         .get_cur_state: get the Current throttle state of the cooling device.
 132         .set_cur_state: set the Current throttle state of the cooling device.
 133
 134 1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
 135
 136     This interface function remove the thermal cooling device.
 137     It deletes the corresponding entry form /sys/class/thermal folder and
 138     unbind itself from all the thermal zone devices using it.
 139
 140 1.3 interface for binding a thermal zone device with a thermal cooling device
 141 1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
 142         int trip, struct thermal_cooling_device *cdev,
 143         unsigned long upper, unsigned long lower, unsigned int weight);
 144
 145     This interface function bind a thermal cooling device to the certain trip
 146     point of a thermal zone device.
 147     This function is usually called in the thermal zone device .bind callback.
 148     tz: the thermal zone device
 149     cdev: thermal cooling device
 150     trip: indicates which trip point the cooling devices is associated with
 151           in this thermal zone.
 152     upper:the Maximum cooling state for this trip point.
 153           THERMAL_NO_LIMIT means no upper limit,
 154           and the cooling device can be in max_state.
 155     lower:the Minimum cooling state can be used for this trip point.
 156           THERMAL_NO_LIMIT means no lower limit,
 157           and the cooling device can be in cooling state 0.
 158     weight: the influence of this cooling device in this thermal
 159             zone.  See 1.4.1 below for more information.
 160
 161 1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
 162                 int trip, struct thermal_cooling_device *cdev);
 163
 164     This interface function unbind a thermal cooling device from the certain
 165     trip point of a thermal zone device. This function is usually called in
 166     the thermal zone device .unbind callback.
 167     tz: the thermal zone device
 168     cdev: thermal cooling device
 169     trip: indicates which trip point the cooling devices is associated with
 170           in this thermal zone.
 171
 172 1.4 Thermal Zone Parameters
 173 1.4.1 struct thermal_bind_params
 174     This structure defines the following parameters that are used to bind
 175     a zone with a cooling device for a particular trip point.
 176     .cdev: The cooling device pointer
 177     .weight: The 'influence' of a particular cooling device on this
 178              zone. This is relative to the rest of the cooling
 179              devices. For example, if all cooling devices have a
 180              weight of 1, then they all contribute the same. You can
 181              use percentages if you want, but it's not mandatory. A
 182              weight of 0 means that this cooling device doesn't
 183              contribute to the cooling of this zone unless all cooling
 184              devices have a weight of 0. If all weights are 0, then
 185              they all contribute the same.
 186     .trip_mask:This is a bit mask that gives the binding relation between
 187                this thermal zone and cdev, for a particular trip point.
 188                If nth bit is set, then the cdev and thermal zone are bound
 189                for trip point n.
 190     .limits: This is an array of cooling state limits. Must have exactly
 191          2 * thermal_zone.number_of_trip_points. It is an array consisting
 192          of tuples <lower-state upper-state> of state limits. Each trip
 193          will be associated with one state limit tuple when binding.
 194          A NULL pointer means <THERMAL_NO_LIMITS THERMAL_NO_LIMITS>
 195          on all trips. These limits are used when binding a cdev to a
 196          trip point.
 197     .match: This call back returns success(0) if the 'tz and cdev' need to
 198             be bound, as per platform data.
 199 1.4.2 struct thermal_zone_params
 200     This structure defines the platform level parameters for a thermal zone.
 201     This data, for each thermal zone should come from the platform layer.
 202     This is an optional feature where some platforms can choose not to
 203     provide this data.
 204     .governor_name: Name of the thermal governor used for this zone
 205     .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
 206                is required. when no_hwmon == false, a hwmon sysfs interface
 207                will be created. when no_hwmon == true, nothing will be done.
 208                In case the thermal_zone_params is NULL, the hwmon interface
 209                will be created (for backward compatibility).
 210     .num_tbps: Number of thermal_bind_params entries for this zone
 211     .tbp: thermal_bind_params entries
 212
 213 2. sysfs attributes structure
 214
 215 RO      read only value
 216 RW      read/write value
 217
 218 Thermal sysfs attributes will be represented under /sys/class/thermal.
 219 Hwmon sysfs I/F extension is also available under /sys/class/hwmon
 220 if hwmon is compiled in or built as a module.
 221
 222 Thermal zone device sys I/F, created once it's registered:
 223 /sys/class/thermal/thermal_zone[0-*]:
 224     |---type:                   Type of the thermal zone
 225     |---temp:                   Current temperature
 226     |---mode:                   Working mode of the thermal zone
 227     |---policy:                 Thermal governor used for this zone
 228     |---available_policies:     Available thermal governors for this zone
 229     |---trip_point_[0-*]_temp:  Trip point temperature
 230     |---trip_point_[0-*]_type:  Trip point type
 231     |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 232     |---emul_temp:              Emulated temperature set node
 233     |---sustainable_power:      Sustainable dissipatable power
 234     |---k_po:                   Proportional term during temperature overshoot
 235     |---k_pu:                   Proportional term during temperature undershoot
 236     |---k_i:                    PID's integral term in the power allocator gov
 237     |---k_d:                    PID's derivative term in the power allocator
 238     |---integral_cutoff:        Offset above which errors are accumulated
 239     |---slope:                  Slope constant applied as linear extrapolation
 240     |---offset:                 Offset constant applied as linear extrapolation
 241
 242 Thermal cooling device sys I/F, created once it's registered:
 243 /sys/class/thermal/cooling_device[0-*]:
 244     |---type:                   Type of the cooling device(processor/fan/...)
 245     |---max_state:              Maximum cooling state of the cooling device
 246     |---cur_state:              Current cooling state of the cooling device
 247
 248
 249 Then next two dynamic attributes are created/removed in pairs. They represent
 250 the relationship between a thermal zone and its associated cooling device.
 251 They are created/removed for each successful execution of
 252 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 253
 254 /sys/class/thermal/thermal_zone[0-*]:
 255     |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 256     |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 257     |---cdev[0-*]_weight:       Influence of the cooling device in
 258                                 this thermal zone
 259
 260 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 261 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 262 of thermal zone device. E.g. the generic thermal driver registers one hwmon
 263 class device and build the associated hwmon sysfs I/F for all the registered
 264 ACPI thermal zones.
 265
 266 /sys/class/hwmon/hwmon[0-*]:
 267     |---name:                   The type of the thermal zone devices
 268     |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 269     |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 270
 271 Please read Documentation/hwmon/sysfs-interface for additional information.
 272
 273 ***************************
 274 * Thermal zone attributes *
 275 ***************************
 276
 277 type
 278         Strings which represent the thermal zone type.
 279         This is given by thermal zone driver as part of registration.
 280         E.g: "acpitz" indicates it's an ACPI thermal device.
 281         In order to keep it consistent with hwmon sys attribute; this should
 282         be a short, lowercase string, not containing spaces nor dashes.
 283         RO, Required
 284
 285 temp
 286         Current temperature as reported by thermal zone (sensor).
 287         Unit: millidegree Celsius
 288         RO, Required
 289
 290 mode
 291         One of the predefined values in [enabled, disabled].
 292         This file gives information about the algorithm that is currently
 293         managing the thermal zone. It can be either default kernel based
 294         algorithm or user space application.
 295         enabled         = enable Kernel Thermal management.
 296         disabled        = Preventing kernel thermal zone driver actions upon
 297                           trip points so that user application can take full
 298                           charge of the thermal management.
 299         RW, Optional
 300
 301 policy
 302         One of the various thermal governors used for a particular zone.
 303         RW, Required
 304
 305 available_policies
 306         Available thermal governors which can be used for a particular zone.
 307         RO, Required
 308
 309 trip_point_[0-*]_temp
 310         The temperature above which trip point will be fired.
 311         Unit: millidegree Celsius
 312         RO, Optional
 313
 314 trip_point_[0-*]_type
 315         Strings which indicate the type of the trip point.
 316         E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 317         thermal zone.
 318         RO, Optional
 319
 320 trip_point_[0-*]_hyst
 321         The hysteresis value for a trip point, represented as an integer
 322         Unit: Celsius
 323         RW, Optional
 324
 325 cdev[0-*]
 326         Sysfs link to the thermal cooling device node where the sys I/F
 327         for cooling device throttling control represents.
 328         RO, Optional
 329
 330 cdev[0-*]_trip_point
 331         The trip point with which cdev[0-*] is associated in this thermal
 332         zone; -1 means the cooling device is not associated with any trip
 333         point.
 334         RO, Optional
 335
 336 cdev[0-*]_weight
 337         The influence of cdev[0-*] in this thermal zone. This value
 338         is relative to the rest of cooling devices in the thermal
 339         zone. For example, if a cooling device has a weight double
 340         than that of other, it's twice as effective in cooling the
 341         thermal zone.
 342         RW, Optional
 343
 344 passive
 345         Attribute is only present for zones in which the passive cooling
 346         policy is not supported by native thermal driver. Default is zero
 347         and can be set to a temperature (in millidegrees) to enable a
 348         passive trip point for the zone. Activation is done by polling with
 349         an interval of 1 second.
 350         Unit: millidegrees Celsius
 351         Valid values: 0 (disabled) or greater than 1000
 352         RW, Optional
 353
 354 emul_temp
 355         Interface to set the emulated temperature method in thermal zone
 356         (sensor). After setting this temperature, the thermal zone may pass
 357         this temperature to platform emulation function if registered or
 358         cache it locally. This is useful in debugging different temperature
 359         threshold and its associated cooling action. This is write only node
 360         and writing 0 on this node should disable emulation.
 361         Unit: millidegree Celsius
 362         WO, Optional
 363
 364           WARNING: Be careful while enabling this option on production systems,
 365           because userland can easily disable the thermal policy by simply
 366           flooding this sysfs node with low temperature values.
 367
 368 sustainable_power
 369         An estimate of the sustained power that can be dissipated by
 370         the thermal zone. Used by the power allocator governor. For
 371         more information see Documentation/thermal/power_allocator.txt
 372         Unit: milliwatts
 373         RW, Optional
 374
 375 k_po
 376         The proportional term of the power allocator governor's PID
 377         controller during temperature overshoot. Temperature overshoot
 378         is when the current temperature is above the "desired
 379         temperature" trip point. For more information see
 380         Documentation/thermal/power_allocator.txt
 381         RW, Optional
 382
 383 k_pu
 384         The proportional term of the power allocator governor's PID
 385         controller during temperature undershoot. Temperature undershoot
 386         is when the current temperature is below the "desired
 387         temperature" trip point. For more information see
 388         Documentation/thermal/power_allocator.txt
 389         RW, Optional
 390
 391 k_i
 392         The integral term of the power allocator governor's PID
 393         controller. This term allows the PID controller to compensate
 394         for long term drift. For more information see
 395         Documentation/thermal/power_allocator.txt
 396         RW, Optional
 397
 398 k_d
 399         The derivative term of the power allocator governor's PID
 400         controller. For more information see
 401         Documentation/thermal/power_allocator.txt
 402         RW, Optional
 403
 404 integral_cutoff
 405         Temperature offset from the desired temperature trip point
 406         above which the integral term of the power allocator
 407         governor's PID controller starts accumulating errors. For
 408         example, if integral_cutoff is 0, then the integral term only
 409         accumulates error when temperature is above the desired
 410         temperature trip point. For more information see
 411         Documentation/thermal/power_allocator.txt
 412         Unit: millidegree Celsius
 413         RW, Optional
 414
 415 slope
 416         The slope constant used in a linear extrapolation model
 417         to determine a hotspot temperature based off the sensor's
 418         raw readings. It is up to the device driver to determine
 419         the usage of these values.
 420         RW, Optional
 421
 422 offset
 423         The offset constant used in a linear extrapolation model
 424         to determine a hotspot temperature based off the sensor's
 425         raw readings. It is up to the device driver to determine
 426         the usage of these values.
 427         RW, Optional
 428
 429 *****************************
 430 * Cooling device attributes *
 431 *****************************
 432
 433 type
 434         String which represents the type of device, e.g:
 435         - for generic ACPI: should be "Fan", "Processor" or "LCD"
 436         - for memory controller device on intel_menlow platform:
 437           should be "Memory controller".
 438         RO, Required
 439
 440 max_state
 441         The maximum permissible cooling state of this cooling device.
 442         RO, Required
 443
 444 cur_state
 445         The current cooling state of this cooling device.
 446         The value can any integer numbers between 0 and max_state:
 447         - cur_state == 0 means no cooling
 448         - cur_state == max_state means the maximum cooling.
 449         RW, Required
 450
 451 3. A simple implementation
 452
 453 ACPI thermal zone may support multiple trip points like critical, hot,
 454 passive, active. If an ACPI thermal zone supports critical, passive,
 455 active[0] and active[1] at the same time, it may register itself as a
 456 thermal_zone_device (thermal_zone1) with 4 trip points in all.
 457 It has one processor and one fan, which are both registered as
 458 thermal_cooling_device. Both are considered to have the same
 459 effectiveness in cooling the thermal zone.
 460
 461 If the processor is listed in _PSL method, and the fan is listed in _AL0
 462 method, the sys I/F structure will be built like this:
 463
 464 /sys/class/thermal:
 465
 466 |thermal_zone1:
 467     |---type:                   acpitz
 468     |---temp:                   37000
 469     |---mode:                   enabled
 470     |---policy:                 step_wise
 471     |---available_policies:     step_wise fair_share
 472     |---trip_point_0_temp:      100000
 473     |---trip_point_0_type:      critical
 474     |---trip_point_1_temp:      80000
 475     |---trip_point_1_type:      passive
 476     |---trip_point_2_temp:      70000
 477     |---trip_point_2_type:      active0
 478     |---trip_point_3_temp:      60000
 479     |---trip_point_3_type:      active1
 480     |---cdev0:                  --->/sys/class/thermal/cooling_device0
 481     |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 482     |---cdev0_weight:           1024
 483     |---cdev1:                  --->/sys/class/thermal/cooling_device3
 484     |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 485     |---cdev1_weight:           1024
 486
 487 |cooling_device0:
 488     |---type:                   Processor
 489     |---max_state:              8
 490     |---cur_state:              0
 491
 492 |cooling_device3:
 493     |---type:                   Fan
 494     |---max_state:              2
 495     |---cur_state:              0
 496
 497 /sys/class/hwmon:
 498
 499 |hwmon0:
 500     |---name:                   acpitz
 501     |---temp1_input:            37000
 502     |---temp1_crit:             100000
 503
 504 4. Event Notification
 505
 506 The framework includes a simple notification mechanism, in the form of a
 507 netlink event. Netlink socket initialization is done during the _init_
 508 of the framework. Drivers which intend to use the notification mechanism
 509 just need to call thermal_generate_netlink_event() with two arguments viz
 510 (originator, event). The originator is a pointer to struct thermal_zone_device
 511 from where the event has been originated. An integer which represents the
 512 thermal zone device will be used in the message to identify the zone. The
 513 event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 514 THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 515 crosses any of the configured thresholds.
 516
 517 5. Export Symbol APIs:
 518
 519 5.1: get_tz_trend:
 520 This function returns the trend of a thermal zone, i.e the rate of change
 521 of temperature of the thermal zone. Ideally, the thermal sensor drivers
 522 are supposed to implement the callback. If they don't, the thermal
 523 framework calculated the trend by comparing the previous and the current
 524 temperature values.
 525
 526 5.2:get_thermal_instance:
 527 This function returns the thermal_instance corresponding to a given
 528 {thermal_zone, cooling_device, trip_point} combination. Returns NULL
 529 if such an instance does not exist.
 530
 531 5.3:thermal_notify_framework:
 532 This function handles the trip events from sensor drivers. It starts
 533 throttling the cooling devices according to the policy configured.
 534 For CRITICAL and HOT trip points, this notifies the respective drivers,
 535 and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
 536 The throttling policy is based on the configured platform data; if no
 537 platform data is provided, this uses the step_wise throttling policy.
 538
 539 5.4:thermal_cdev_update:
 540 This function serves as an arbitrator to set the state of a cooling
 541 device. It sets the cooling device to the deepest cooling state if
 542 possible.