1=================================== 2Generic Thermal Sysfs driver How To 3=================================== 4 5Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com> 6 7Updated: 2 January 2008 8 9Copyright (c) 2008 Intel Corporation 10 11 120. Introduction 13=============== 14 15The generic thermal sysfs provides a set of interfaces for thermal zone 16devices (sensors) and thermal cooling devices (fan, processor...) to register 17with the thermal management solution and to be a part of it. 18 19This how-to focuses on enabling new thermal zone and cooling devices to 20participate in thermal management. 21This solution is platform independent and any type of thermal zone devices 22and cooling devices should be able to make use of the infrastructure. 23 24The main task of the thermal sysfs driver is to expose thermal zone attributes 25as well as cooling device attributes to the user space. 26An intelligent thermal management application can make decisions based on 27inputs from thermal zone attributes (the current temperature and trip point 28temperature) and throttle appropriate devices. 29 30- `[0-*]` denotes any positive number starting from 0 31- `[1-*]` denotes any positive number starting from 1 32 331. thermal sysfs driver interface functions 34=========================================== 35 361.1 thermal zone device interface 37--------------------------------- 38 39 :: 40 41 struct thermal_zone_device 42 *thermal_zone_device_register(char *type, 43 int trips, int mask, void *devdata, 44 struct thermal_zone_device_ops *ops, 45 const struct thermal_zone_params *tzp, 46 int passive_delay, int polling_delay)) 47 48 This interface function adds a new thermal zone device (sensor) to 49 /sys/class/thermal folder as `thermal_zone[0-*]`. It tries to bind all the 50 thermal cooling devices registered at the same time. 51 52 type: 53 the thermal zone type. 54 trips: 55 the total number of trip points this thermal zone supports. 56 mask: 57 Bit string: If 'n'th bit is set, then trip point 'n' is writable. 58 devdata: 59 device private data 60 ops: 61 thermal zone device call-backs. 62 63 .bind: 64 bind the thermal zone device with a thermal cooling device. 65 .unbind: 66 unbind the thermal zone device with a thermal cooling device. 67 .get_temp: 68 get the current temperature of the thermal zone. 69 .set_trips: 70 set the trip points window. Whenever the current temperature 71 is updated, the trip points immediately below and above the 72 current temperature are found. 73 .get_mode: 74 get the current mode (enabled/disabled) of the thermal zone. 75 76 - "enabled" means the kernel thermal management is 77 enabled. 78 - "disabled" will prevent kernel thermal driver action 79 upon trip points so that user applications can take 80 charge of thermal management. 81 .set_mode: 82 set the mode (enabled/disabled) of the thermal zone. 83 .get_trip_type: 84 get the type of certain trip point. 85 .get_trip_temp: 86 get the temperature above which the certain trip point 87 will be fired. 88 .set_emul_temp: 89 set the emulation temperature which helps in debugging 90 different threshold temperature points. 91 tzp: 92 thermal zone platform parameters. 93 passive_delay: 94 number of milliseconds to wait between polls when 95 performing passive cooling. 96 polling_delay: 97 number of milliseconds to wait between polls when checking 98 whether trip points have been crossed (0 for interrupt driven systems). 99 100 :: 101 102 void thermal_zone_device_unregister(struct thermal_zone_device *tz) 103 104 This interface function removes the thermal zone device. 105 It deletes the corresponding entry from /sys/class/thermal folder and 106 unbinds all the thermal cooling devices it uses. 107 108 :: 109 110 struct thermal_zone_device 111 *thermal_zone_of_sensor_register(struct device *dev, int sensor_id, 112 void *data, 113 const struct thermal_zone_of_device_ops *ops) 114 115 This interface adds a new sensor to a DT thermal zone. 116 This function will search the list of thermal zones described in 117 device tree and look for the zone that refer to the sensor device 118 pointed by dev->of_node as temperature providers. For the zone 119 pointing to the sensor node, the sensor will be added to the DT 120 thermal zone device. 121 122 The parameters for this interface are: 123 124 dev: 125 Device node of sensor containing valid node pointer in 126 dev->of_node. 127 sensor_id: 128 a sensor identifier, in case the sensor IP has more 129 than one sensors 130 data: 131 a private pointer (owned by the caller) that will be 132 passed back, when a temperature reading is needed. 133 ops: 134 `struct thermal_zone_of_device_ops *`. 135 136 ============== ======================================= 137 get_temp a pointer to a function that reads the 138 sensor temperature. This is mandatory 139 callback provided by sensor driver. 140 set_trips a pointer to a function that sets a 141 temperature window. When this window is 142 left the driver must inform the thermal 143 core via thermal_zone_device_update. 144 get_trend a pointer to a function that reads the 145 sensor temperature trend. 146 set_emul_temp a pointer to a function that sets 147 sensor emulated temperature. 148 ============== ======================================= 149 150 The thermal zone temperature is provided by the get_temp() function 151 pointer of thermal_zone_of_device_ops. When called, it will 152 have the private pointer @data back. 153 154 It returns error pointer if fails otherwise valid thermal zone device 155 handle. Caller should check the return handle with IS_ERR() for finding 156 whether success or not. 157 158 :: 159 160 void thermal_zone_of_sensor_unregister(struct device *dev, 161 struct thermal_zone_device *tzd) 162 163 This interface unregisters a sensor from a DT thermal zone which was 164 successfully added by interface thermal_zone_of_sensor_register(). 165 This function removes the sensor callbacks and private data from the 166 thermal zone device registered with thermal_zone_of_sensor_register() 167 interface. It will also silent the zone by remove the .get_temp() and 168 get_trend() thermal zone device callbacks. 169 170 :: 171 172 struct thermal_zone_device 173 *devm_thermal_zone_of_sensor_register(struct device *dev, 174 int sensor_id, 175 void *data, 176 const struct thermal_zone_of_device_ops *ops) 177 178 This interface is resource managed version of 179 thermal_zone_of_sensor_register(). 180 181 All details of thermal_zone_of_sensor_register() described in 182 section 1.1.3 is applicable here. 183 184 The benefit of using this interface to register sensor is that it 185 is not require to explicitly call thermal_zone_of_sensor_unregister() 186 in error path or during driver unbinding as this is done by driver 187 resource manager. 188 189 :: 190 191 void devm_thermal_zone_of_sensor_unregister(struct device *dev, 192 struct thermal_zone_device *tzd) 193 194 This interface is resource managed version of 195 thermal_zone_of_sensor_unregister(). 196 All details of thermal_zone_of_sensor_unregister() described in 197 section 1.1.4 is applicable here. 198 Normally this function will not need to be called and the resource 199 management code will ensure that the resource is freed. 200 201 :: 202 203 int thermal_zone_get_slope(struct thermal_zone_device *tz) 204 205 This interface is used to read the slope attribute value 206 for the thermal zone device, which might be useful for platform 207 drivers for temperature calculations. 208 209 :: 210 211 int thermal_zone_get_offset(struct thermal_zone_device *tz) 212 213 This interface is used to read the offset attribute value 214 for the thermal zone device, which might be useful for platform 215 drivers for temperature calculations. 216 2171.2 thermal cooling device interface 218------------------------------------ 219 220 221 :: 222 223 struct thermal_cooling_device 224 *thermal_cooling_device_register(char *name, 225 void *devdata, struct thermal_cooling_device_ops *) 226 227 This interface function adds a new thermal cooling device (fan/processor/...) 228 to /sys/class/thermal/ folder as `cooling_device[0-*]`. It tries to bind itself 229 to all the thermal zone devices registered at the same time. 230 231 name: 232 the cooling device name. 233 devdata: 234 device private data. 235 ops: 236 thermal cooling devices call-backs. 237 238 .get_max_state: 239 get the Maximum throttle state of the cooling device. 240 .get_cur_state: 241 get the Currently requested throttle state of the 242 cooling device. 243 .set_cur_state: 244 set the Current throttle state of the cooling device. 245 246 :: 247 248 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev) 249 250 This interface function removes the thermal cooling device. 251 It deletes the corresponding entry from /sys/class/thermal folder and 252 unbinds itself from all the thermal zone devices using it. 253 2541.3 interface for binding a thermal zone device with a thermal cooling device 255----------------------------------------------------------------------------- 256 257 :: 258 259 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz, 260 int trip, struct thermal_cooling_device *cdev, 261 unsigned long upper, unsigned long lower, unsigned int weight); 262 263 This interface function binds a thermal cooling device to a particular trip 264 point of a thermal zone device. 265 266 This function is usually called in the thermal zone device .bind callback. 267 268 tz: 269 the thermal zone device 270 cdev: 271 thermal cooling device 272 trip: 273 indicates which trip point in this thermal zone the cooling device 274 is associated with. 275 upper: 276 the Maximum cooling state for this trip point. 277 THERMAL_NO_LIMIT means no upper limit, 278 and the cooling device can be in max_state. 279 lower: 280 the Minimum cooling state can be used for this trip point. 281 THERMAL_NO_LIMIT means no lower limit, 282 and the cooling device can be in cooling state 0. 283 weight: 284 the influence of this cooling device in this thermal 285 zone. See 1.4.1 below for more information. 286 287 :: 288 289 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz, 290 int trip, struct thermal_cooling_device *cdev); 291 292 This interface function unbinds a thermal cooling device from a particular 293 trip point of a thermal zone device. This function is usually called in 294 the thermal zone device .unbind callback. 295 296 tz: 297 the thermal zone device 298 cdev: 299 thermal cooling device 300 trip: 301 indicates which trip point in this thermal zone the cooling device 302 is associated with. 303 3041.4 Thermal Zone Parameters 305--------------------------- 306 307 :: 308 309 struct thermal_zone_params 310 311 This structure defines the platform level parameters for a thermal zone. 312 This data, for each thermal zone should come from the platform layer. 313 This is an optional feature where some platforms can choose not to 314 provide this data. 315 316 .governor_name: 317 Name of the thermal governor used for this zone 318 .no_hwmon: 319 a boolean to indicate if the thermal to hwmon sysfs interface 320 is required. when no_hwmon == false, a hwmon sysfs interface 321 will be created. when no_hwmon == true, nothing will be done. 322 In case the thermal_zone_params is NULL, the hwmon interface 323 will be created (for backward compatibility). 324 3252. sysfs attributes structure 326============================= 327 328== ================ 329RO read only value 330WO write only value 331RW read/write value 332== ================ 333 334Thermal sysfs attributes will be represented under /sys/class/thermal. 335Hwmon sysfs I/F extension is also available under /sys/class/hwmon 336if hwmon is compiled in or built as a module. 337 338Thermal zone device sys I/F, created once it's registered:: 339 340 /sys/class/thermal/thermal_zone[0-*]: 341 |---type: Type of the thermal zone 342 |---temp: Current temperature 343 |---mode: Working mode of the thermal zone 344 |---policy: Thermal governor used for this zone 345 |---available_policies: Available thermal governors for this zone 346 |---trip_point_[0-*]_temp: Trip point temperature 347 |---trip_point_[0-*]_type: Trip point type 348 |---trip_point_[0-*]_hyst: Hysteresis value for this trip point 349 |---emul_temp: Emulated temperature set node 350 |---sustainable_power: Sustainable dissipatable power 351 |---k_po: Proportional term during temperature overshoot 352 |---k_pu: Proportional term during temperature undershoot 353 |---k_i: PID's integral term in the power allocator gov 354 |---k_d: PID's derivative term in the power allocator 355 |---integral_cutoff: Offset above which errors are accumulated 356 |---slope: Slope constant applied as linear extrapolation 357 |---offset: Offset constant applied as linear extrapolation 358 359Thermal cooling device sys I/F, created once it's registered:: 360 361 /sys/class/thermal/cooling_device[0-*]: 362 |---type: Type of the cooling device(processor/fan/...) 363 |---max_state: Maximum cooling state of the cooling device 364 |---cur_state: Current cooling state of the cooling device 365 |---stats: Directory containing cooling device's statistics 366 |---stats/reset: Writing any value resets the statistics 367 |---stats/time_in_state_ms: Time (msec) spent in various cooling states 368 |---stats/total_trans: Total number of times cooling state is changed 369 |---stats/trans_table: Cooling state transition table 370 371 372Then next two dynamic attributes are created/removed in pairs. They represent 373the relationship between a thermal zone and its associated cooling device. 374They are created/removed for each successful execution of 375thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device. 376 377:: 378 379 /sys/class/thermal/thermal_zone[0-*]: 380 |---cdev[0-*]: [0-*]th cooling device in current thermal zone 381 |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with 382 |---cdev[0-*]_weight: Influence of the cooling device in 383 this thermal zone 384 385Besides the thermal zone device sysfs I/F and cooling device sysfs I/F, 386the generic thermal driver also creates a hwmon sysfs I/F for each _type_ 387of thermal zone device. E.g. the generic thermal driver registers one hwmon 388class device and build the associated hwmon sysfs I/F for all the registered 389ACPI thermal zones. 390 391Please read Documentation/ABI/testing/sysfs-class-thermal for thermal 392zone and cooling device attribute details. 393 394:: 395 396 /sys/class/hwmon/hwmon[0-*]: 397 |---name: The type of the thermal zone devices 398 |---temp[1-*]_input: The current temperature of thermal zone [1-*] 399 |---temp[1-*]_critical: The critical trip point of thermal zone [1-*] 400 401Please read Documentation/hwmon/sysfs-interface.rst for additional information. 402 4033. A simple implementation 404========================== 405 406ACPI thermal zone may support multiple trip points like critical, hot, 407passive, active. If an ACPI thermal zone supports critical, passive, 408active[0] and active[1] at the same time, it may register itself as a 409thermal_zone_device (thermal_zone1) with 4 trip points in all. 410It has one processor and one fan, which are both registered as 411thermal_cooling_device. Both are considered to have the same 412effectiveness in cooling the thermal zone. 413 414If the processor is listed in _PSL method, and the fan is listed in _AL0 415method, the sys I/F structure will be built like this:: 416 417 /sys/class/thermal: 418 |thermal_zone1: 419 |---type: acpitz 420 |---temp: 37000 421 |---mode: enabled 422 |---policy: step_wise 423 |---available_policies: step_wise fair_share 424 |---trip_point_0_temp: 100000 425 |---trip_point_0_type: critical 426 |---trip_point_1_temp: 80000 427 |---trip_point_1_type: passive 428 |---trip_point_2_temp: 70000 429 |---trip_point_2_type: active0 430 |---trip_point_3_temp: 60000 431 |---trip_point_3_type: active1 432 |---cdev0: --->/sys/class/thermal/cooling_device0 433 |---cdev0_trip_point: 1 /* cdev0 can be used for passive */ 434 |---cdev0_weight: 1024 435 |---cdev1: --->/sys/class/thermal/cooling_device3 436 |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/ 437 |---cdev1_weight: 1024 438 439 |cooling_device0: 440 |---type: Processor 441 |---max_state: 8 442 |---cur_state: 0 443 444 |cooling_device3: 445 |---type: Fan 446 |---max_state: 2 447 |---cur_state: 0 448 449 /sys/class/hwmon: 450 |hwmon0: 451 |---name: acpitz 452 |---temp1_input: 37000 453 |---temp1_crit: 100000 454 4554. Export Symbol APIs 456===================== 457 4584.1. get_tz_trend 459----------------- 460 461This function returns the trend of a thermal zone, i.e the rate of change 462of temperature of the thermal zone. Ideally, the thermal sensor drivers 463are supposed to implement the callback. If they don't, the thermal 464framework calculated the trend by comparing the previous and the current 465temperature values. 466 4674.2. get_thermal_instance 468------------------------- 469 470This function returns the thermal_instance corresponding to a given 471{thermal_zone, cooling_device, trip_point} combination. Returns NULL 472if such an instance does not exist. 473 4744.3. thermal_cdev_update 475------------------------ 476 477This function serves as an arbitrator to set the state of a cooling 478device. It sets the cooling device to the deepest cooling state if 479possible. 480 4815. thermal_emergency_poweroff 482============================= 483 484On an event of critical trip temperature crossing the thermal framework 485shuts down the system by calling hw_protection_shutdown(). The 486hw_protection_shutdown() first attempts to perform an orderly shutdown 487but accepts a delay after which it proceeds doing a forced power-off 488or as last resort an emergency_restart. 489 490The delay should be carefully profiled so as to give adequate time for 491orderly poweroff. 492 493If the delay is set to 0 emergency poweroff will not be supported. So a 494carefully profiled non-zero positive value is a must for emergency 495poweroff to be triggered. 496