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     |---available_policies:     Available thermal governors for this zone
 184     |---trip_point_[0-*]_temp:  Trip point temperature
 185     |---trip_point_[0-*]_type:  Trip point type
 186     |---trip_point_[0-*]_hyst:  Hysteresis value for this trip point
 187     |---emul_temp:              Emulated temperature set node
 188     |---sustainable_power:      Sustainable dissipatable power
 189     |---k_po:                   Proportional term during temperature overshoot
 190     |---k_pu:                   Proportional term during temperature undershoot
 191     |---k_i:                    PID's integral term in the power allocator gov
 192     |---k_d:                    PID's derivative term in the power allocator
 193     |---integral_cutoff:        Offset above which errors are accumulated
 194     |---slope:                  Slope constant applied as linear extrapolation
 195     |---offset:                 Offset constant applied as linear extrapolation
 196
 197 Thermal cooling device sys I/F, created once it's registered:
 198 /sys/class/thermal/cooling_device[0-*]:
 199     |---type:                   Type of the cooling device(processor/fan/...)
 200     |---max_state:              Maximum cooling state of the cooling device
 201     |---cur_state:              Current cooling state of the cooling device
 202
 203
 204 Then next two dynamic attributes are created/removed in pairs. They represent
 205 the relationship between a thermal zone and its associated cooling device.
 206 They are created/removed for each successful execution of
 207 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
 208
 209 /sys/class/thermal/thermal_zone[0-*]:
 210     |---cdev[0-*]:              [0-*]th cooling device in current thermal zone
 211     |---cdev[0-*]_trip_point:   Trip point that cdev[0-*] is associated with
 212     |---cdev[0-*]_weight:       Influence of the cooling device in
 213                                 this thermal zone
 214
 215 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
 216 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
 217 of thermal zone device. E.g. the generic thermal driver registers one hwmon
 218 class device and build the associated hwmon sysfs I/F for all the registered
 219 ACPI thermal zones.
 220
 221 /sys/class/hwmon/hwmon[0-*]:
 222     |---name:                   The type of the thermal zone devices
 223     |---temp[1-*]_input:        The current temperature of thermal zone [1-*]
 224     |---temp[1-*]_critical:     The critical trip point of thermal zone [1-*]
 225
 226 Please read Documentation/hwmon/sysfs-interface for additional information.
 227
 228 ***************************
 229 * Thermal zone attributes *
 230 ***************************
 231
 232 type
 233         Strings which represent the thermal zone type.
 234         This is given by thermal zone driver as part of registration.
 235         E.g: "acpitz" indicates it's an ACPI thermal device.
 236         In order to keep it consistent with hwmon sys attribute; this should
 237         be a short, lowercase string, not containing spaces nor dashes.
 238         RO, Required
 239
 240 temp
 241         Current temperature as reported by thermal zone (sensor).
 242         Unit: millidegree Celsius
 243         RO, Required
 244
 245 mode
 246         One of the predefined values in [enabled, disabled].
 247         This file gives information about the algorithm that is currently
 248         managing the thermal zone. It can be either default kernel based
 249         algorithm or user space application.
 250         enabled         = enable Kernel Thermal management.
 251         disabled        = Preventing kernel thermal zone driver actions upon
 252                           trip points so that user application can take full
 253                           charge of the thermal management.
 254         RW, Optional
 255
 256 policy
 257         One of the various thermal governors used for a particular zone.
 258         RW, Required
 259
 260 available_policies
 261         Available thermal governors which can be used for a particular zone.
 262         RO, Required
 263
 264 trip_point_[0-*]_temp
 265         The temperature above which trip point will be fired.
 266         Unit: millidegree Celsius
 267         RO, Optional
 268
 269 trip_point_[0-*]_type
 270         Strings which indicate the type of the trip point.
 271         E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
 272         thermal zone.
 273         RO, Optional
 274
 275 trip_point_[0-*]_hyst
 276         The hysteresis value for a trip point, represented as an integer
 277         Unit: Celsius
 278         RW, Optional
 279
 280 cdev[0-*]
 281         Sysfs link to the thermal cooling device node where the sys I/F
 282         for cooling device throttling control represents.
 283         RO, Optional
 284
 285 cdev[0-*]_trip_point
 286         The trip point with which cdev[0-*] is associated in this thermal
 287         zone; -1 means the cooling device is not associated with any trip
 288         point.
 289         RO, Optional
 290
 291 cdev[0-*]_weight
 292         The influence of cdev[0-*] in this thermal zone. This value
 293         is relative to the rest of cooling devices in the thermal
 294         zone. For example, if a cooling device has a weight double
 295         than that of other, it's twice as effective in cooling the
 296         thermal zone.
 297         RW, Optional
 298
 299 passive
 300         Attribute is only present for zones in which the passive cooling
 301         policy is not supported by native thermal driver. Default is zero
 302         and can be set to a temperature (in millidegrees) to enable a
 303         passive trip point for the zone. Activation is done by polling with
 304         an interval of 1 second.
 305         Unit: millidegrees Celsius
 306         Valid values: 0 (disabled) or greater than 1000
 307         RW, Optional
 308
 309 emul_temp
 310         Interface to set the emulated temperature method in thermal zone
 311         (sensor). After setting this temperature, the thermal zone may pass
 312         this temperature to platform emulation function if registered or
 313         cache it locally. This is useful in debugging different temperature
 314         threshold and its associated cooling action. This is write only node
 315         and writing 0 on this node should disable emulation.
 316         Unit: millidegree Celsius
 317         WO, Optional
 318
 319           WARNING: Be careful while enabling this option on production systems,
 320           because userland can easily disable the thermal policy by simply
 321           flooding this sysfs node with low temperature values.
 322
 323 sustainable_power
 324         An estimate of the sustained power that can be dissipated by
 325         the thermal zone. Used by the power allocator governor. For
 326         more information see Documentation/thermal/power_allocator.txt
 327         Unit: milliwatts
 328         RW, Optional
 329
 330 k_po
 331         The proportional term of the power allocator governor's PID
 332         controller during temperature overshoot. Temperature overshoot
 333         is when the current temperature is above the "desired
 334         temperature" trip point. For more information see
 335         Documentation/thermal/power_allocator.txt
 336         RW, Optional
 337
 338 k_pu
 339         The proportional term of the power allocator governor's PID
 340         controller during temperature undershoot. Temperature undershoot
 341         is when the current temperature is below the "desired
 342         temperature" trip point. For more information see
 343         Documentation/thermal/power_allocator.txt
 344         RW, Optional
 345
 346 k_i
 347         The integral term of the power allocator governor's PID
 348         controller. This term allows the PID controller to compensate
 349         for long term drift. For more information see
 350         Documentation/thermal/power_allocator.txt
 351         RW, Optional
 352
 353 k_d
 354         The derivative term of the power allocator governor's PID
 355         controller. For more information see
 356         Documentation/thermal/power_allocator.txt
 357         RW, Optional
 358
 359 integral_cutoff
 360         Temperature offset from the desired temperature trip point
 361         above which the integral term of the power allocator
 362         governor's PID controller starts accumulating errors. For
 363         example, if integral_cutoff is 0, then the integral term only
 364         accumulates error when temperature is above the desired
 365         temperature trip point. For more information see
 366         Documentation/thermal/power_allocator.txt
 367         RW, Optional
 368
 369 slope
 370         The slope constant used in a linear extrapolation model
 371         to determine a hotspot temperature based off the sensor's
 372         raw readings. It is up to the device driver to determine
 373         the usage of these values.
 374         RW, Optional
 375
 376 offset
 377         The offset constant used in a linear extrapolation model
 378         to determine a hotspot temperature based off the sensor's
 379         raw readings. It is up to the device driver to determine
 380         the usage of these values.
 381         RW, Optional
 382
 383 *****************************
 384 * Cooling device attributes *
 385 *****************************
 386
 387 type
 388         String which represents the type of device, e.g:
 389         - for generic ACPI: should be "Fan", "Processor" or "LCD"
 390         - for memory controller device on intel_menlow platform:
 391           should be "Memory controller".
 392         RO, Required
 393
 394 max_state
 395         The maximum permissible cooling state of this cooling device.
 396         RO, Required
 397
 398 cur_state
 399         The current cooling state of this cooling device.
 400         The value can any integer numbers between 0 and max_state:
 401         - cur_state == 0 means no cooling
 402         - cur_state == max_state means the maximum cooling.
 403         RW, Required
 404
 405 3. A simple implementation
 406
 407 ACPI thermal zone may support multiple trip points like critical, hot,
 408 passive, active. If an ACPI thermal zone supports critical, passive,
 409 active[0] and active[1] at the same time, it may register itself as a
 410 thermal_zone_device (thermal_zone1) with 4 trip points in all.
 411 It has one processor and one fan, which are both registered as
 412 thermal_cooling_device. Both are considered to have the same
 413 effectiveness in cooling the thermal zone.
 414
 415 If the processor is listed in _PSL method, and the fan is listed in _AL0
 416 method, the sys I/F structure will be built like this:
 417
 418 /sys/class/thermal:
 419
 420 |thermal_zone1:
 421     |---type:                   acpitz
 422     |---temp:                   37000
 423     |---mode:                   enabled
 424     |---policy:                 step_wise
 425     |---available_policies:     step_wise fair_share
 426     |---trip_point_0_temp:      100000
 427     |---trip_point_0_type:      critical
 428     |---trip_point_1_temp:      80000
 429     |---trip_point_1_type:      passive
 430     |---trip_point_2_temp:      70000
 431     |---trip_point_2_type:      active0
 432     |---trip_point_3_temp:      60000
 433     |---trip_point_3_type:      active1
 434     |---cdev0:                  --->/sys/class/thermal/cooling_device0
 435     |---cdev0_trip_point:       1       /* cdev0 can be used for passive */
 436     |---cdev0_weight:           1024
 437     |---cdev1:                  --->/sys/class/thermal/cooling_device3
 438     |---cdev1_trip_point:       2       /* cdev1 can be used for active[0]*/
 439     |---cdev1_weight:           1024
 440
 441 |cooling_device0:
 442     |---type:                   Processor
 443     |---max_state:              8
 444     |---cur_state:              0
 445
 446 |cooling_device3:
 447     |---type:                   Fan
 448     |---max_state:              2
 449     |---cur_state:              0
 450
 451 /sys/class/hwmon:
 452
 453 |hwmon0:
 454     |---name:                   acpitz
 455     |---temp1_input:            37000
 456     |---temp1_crit:             100000
 457
 458 4. Event Notification
 459
 460 The framework includes a simple notification mechanism, in the form of a
 461 netlink event. Netlink socket initialization is done during the _init_
 462 of the framework. Drivers which intend to use the notification mechanism
 463 just need to call thermal_generate_netlink_event() with two arguments viz
 464 (originator, event). The originator is a pointer to struct thermal_zone_device
 465 from where the event has been originated. An integer which represents the
 466 thermal zone device will be used in the message to identify the zone. The
 467 event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
 468 THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
 469 crosses any of the configured thresholds.
 470
 471 5. Export Symbol APIs:
 472
 473 5.1: get_tz_trend:
 474 This function returns the trend of a thermal zone, i.e the rate of change
 475 of temperature of the thermal zone. Ideally, the thermal sensor drivers
 476 are supposed to implement the callback. If they don't, the thermal
 477 framework calculated the trend by comparing the previous and the current
 478 temperature values.
 479
 480 5.2:get_thermal_instance:
 481 This function returns the thermal_instance corresponding to a given
 482 {thermal_zone, cooling_device, trip_point} combination. Returns NULL
 483 if such an instance does not exist.
 484
 485 5.3:thermal_notify_framework:
 486 This function handles the trip events from sensor drivers. It starts
 487 throttling the cooling devices according to the policy configured.
 488 For CRITICAL and HOT trip points, this notifies the respective drivers,
 489 and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
 490 The throttling policy is based on the configured platform data; if no
 491 platform data is provided, this uses the step_wise throttling policy.
 492
 493 5.4:thermal_cdev_update:
 494 This function serves as an arbitrator to set the state of a cooling
 495 device. It sets the cooling device to the deepest cooling state if
 496 possible.