1Generic Thermal Sysfs driver How To 2=================================== 3 4Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com> 5 6Updated: 2 January 2008 7 8Copyright (c) 2008 Intel Corporation 9 10 110. Introduction 12 13The generic thermal sysfs provides a set of interfaces for thermal zone 14devices (sensors) and thermal cooling devices (fan, processor...) to register 15with the thermal management solution and to be a part of it. 16 17This how-to focuses on enabling new thermal zone and cooling devices to 18participate in thermal management. 19This solution is platform independent and any type of thermal zone devices 20and cooling devices should be able to make use of the infrastructure. 21 22The main task of the thermal sysfs driver is to expose thermal zone attributes 23as well as cooling device attributes to the user space. 24An intelligent thermal management application can make decisions based on 25inputs from thermal zone attributes (the current temperature and trip point 26temperature) and throttle appropriate devices. 27 28[0-*] denotes any positive number starting from 0 29[1-*] denotes any positive number starting from 1 30 311. thermal sysfs driver interface functions 32 331.1 thermal zone device interface 341.1.1 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 68 691.1.2 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. 74 751.2 thermal cooling device interface 761.2.1 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. 88 891.2.2 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. 94 951.3 interface for binding a thermal zone device with a thermal cooling device 961.3.1 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 1161.3.2 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 1271.4 Thermal Zone Parameters 1281.4.1 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. 1541.4.2 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 1682. sysfs attributes structure 169 170RO read only value 171RW read/write value 172 173Thermal sysfs attributes will be represented under /sys/class/thermal. 174Hwmon sysfs I/F extension is also available under /sys/class/hwmon 175if hwmon is compiled in or built as a module. 176 177Thermal 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 197Thermal 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 204Then next two dynamic attributes are created/removed in pairs. They represent 205the relationship between a thermal zone and its associated cooling device. 206They are created/removed for each successful execution of 207thermal_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 215Besides the thermal zone device sysfs I/F and cooling device sysfs I/F, 216the generic thermal driver also creates a hwmon sysfs I/F for each _type_ 217of thermal zone device. E.g. the generic thermal driver registers one hwmon 218class device and build the associated hwmon sysfs I/F for all the registered 219ACPI 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 226Please read Documentation/hwmon/sysfs-interface for additional information. 227 228*************************** 229* Thermal zone attributes * 230*************************** 231 232type 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 240temp 241 Current temperature as reported by thermal zone (sensor). 242 Unit: millidegree Celsius 243 RO, Required 244 245mode 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 256policy 257 One of the various thermal governors used for a particular zone. 258 RW, Required 259 260available_policies 261 Available thermal governors which can be used for a particular zone. 262 RO, Required 263 264trip_point_[0-*]_temp 265 The temperature above which trip point will be fired. 266 Unit: millidegree Celsius 267 RO, Optional 268 269trip_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 275trip_point_[0-*]_hyst 276 The hysteresis value for a trip point, represented as an integer 277 Unit: Celsius 278 RW, Optional 279 280cdev[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 285cdev[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 291cdev[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 299passive 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 309emul_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 323sustainable_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 330k_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 338k_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 346k_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 353k_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 359integral_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 369slope 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 376offset 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 387type 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 394max_state 395 The maximum permissible cooling state of this cooling device. 396 RO, Required 397 398cur_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 4053. A simple implementation 406 407ACPI thermal zone may support multiple trip points like critical, hot, 408passive, active. If an ACPI thermal zone supports critical, passive, 409active[0] and active[1] at the same time, it may register itself as a 410thermal_zone_device (thermal_zone1) with 4 trip points in all. 411It has one processor and one fan, which are both registered as 412thermal_cooling_device. Both are considered to have the same 413effectiveness in cooling the thermal zone. 414 415If the processor is listed in _PSL method, and the fan is listed in _AL0 416method, 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 4584. Event Notification 459 460The framework includes a simple notification mechanism, in the form of a 461netlink event. Netlink socket initialization is done during the _init_ 462of the framework. Drivers which intend to use the notification mechanism 463just need to call thermal_generate_netlink_event() with two arguments viz 464(originator, event). The originator is a pointer to struct thermal_zone_device 465from where the event has been originated. An integer which represents the 466thermal zone device will be used in the message to identify the zone. The 467event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL, 468THERMAL_DEV_FAULT}. Notification can be sent when the current temperature 469crosses any of the configured thresholds. 470 4715. Export Symbol APIs: 472 4735.1: get_tz_trend: 474This function returns the trend of a thermal zone, i.e the rate of change 475of temperature of the thermal zone. Ideally, the thermal sensor drivers 476are supposed to implement the callback. If they don't, the thermal 477framework calculated the trend by comparing the previous and the current 478temperature values. 479 4805.2:get_thermal_instance: 481This function returns the thermal_instance corresponding to a given 482{thermal_zone, cooling_device, trip_point} combination. Returns NULL 483if such an instance does not exist. 484 4855.3:thermal_notify_framework: 486This function handles the trip events from sensor drivers. It starts 487throttling the cooling devices according to the policy configured. 488For CRITICAL and HOT trip points, this notifies the respective drivers, 489and does actual throttling for other trip points i.e ACTIVE and PASSIVE. 490The throttling policy is based on the configured platform data; if no 491platform data is provided, this uses the step_wise throttling policy. 492 4935.4:thermal_cdev_update: 494This function serves as an arbitrator to set the state of a cooling 495device. It sets the cooling device to the deepest cooling state if 496possible. 497