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