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2 Generic Thermal Sysfs driver How To 2 Generic Thermal Sysfs driver How To
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4 4
5 Written by Sujith Thomas <sujith.thomas@intel.c 5 Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
6 6
7 Copyright (c) 2008 Intel Corporation 7 Copyright (c) 2008 Intel Corporation
8 8
9 9
10 0. Introduction 10 0. Introduction
11 =============== 11 ===============
12 12
13 The generic thermal sysfs provides a set of in 13 The generic thermal sysfs provides a set of interfaces for thermal zone
14 devices (sensors) and thermal cooling devices 14 devices (sensors) and thermal cooling devices (fan, processor...) to register
15 with the thermal management solution and to be 15 with the thermal management solution and to be a part of it.
16 16
17 This how-to focuses on enabling new thermal zo 17 This how-to focuses on enabling new thermal zone and cooling devices to
18 participate in thermal management. 18 participate in thermal management.
19 This solution is platform independent and any 19 This solution is platform independent and any type of thermal zone devices
20 and cooling devices should be able to make use 20 and cooling devices should be able to make use of the infrastructure.
21 21
22 The main task of the thermal sysfs driver is t 22 The main task of the thermal sysfs driver is to expose thermal zone attributes
23 as well as cooling device attributes to the us 23 as well as cooling device attributes to the user space.
24 An intelligent thermal management application 24 An intelligent thermal management application can make decisions based on
25 inputs from thermal zone attributes (the curre 25 inputs from thermal zone attributes (the current temperature and trip point
26 temperature) and throttle appropriate devices. 26 temperature) and throttle appropriate devices.
27 27
28 - `[0-*]` denotes any positive number st 28 - `[0-*]` denotes any positive number starting from 0
29 - `[1-*]` denotes any positive number st 29 - `[1-*]` denotes any positive number starting from 1
30 30
31 1. thermal sysfs driver interface functions 31 1. thermal sysfs driver interface functions
32 =========================================== 32 ===========================================
33 33
34 1.1 thermal zone device interface 34 1.1 thermal zone device interface
35 --------------------------------- 35 ---------------------------------
36 36
37 :: 37 ::
38 38
39 struct thermal_zone_device * 39 struct thermal_zone_device *
40 thermal_zone_device_register_with_trip 40 thermal_zone_device_register_with_trips(const char *type,
41 const 41 const struct thermal_trip *trips,
42 int nu 42 int num_trips, void *devdata,
43 const 43 const struct thermal_zone_device_ops *ops,
44 const 44 const struct thermal_zone_params *tzp,
45 unsign 45 unsigned int passive_delay,
46 unsign 46 unsigned int polling_delay)
47 47
48 This interface function adds a new thermal 48 This interface function adds a new thermal zone device (sensor) to the
49 /sys/class/thermal folder as `thermal_zone 49 /sys/class/thermal folder as `thermal_zone[0-*]`. It tries to bind all the
50 thermal cooling devices registered to it a 50 thermal cooling devices registered to it at the same time.
51 51
52 type: 52 type:
53 the thermal zone type. 53 the thermal zone type.
54 trips: 54 trips:
55 the table of trip points for this ther 55 the table of trip points for this thermal zone.
56 devdata: 56 devdata:
57 device private data 57 device private data
58 ops: 58 ops:
59 thermal zone device call-backs. 59 thermal zone device call-backs.
60 60
61 .should_bind: 61 .should_bind:
62 check whether or not a given c 62 check whether or not a given cooling device should be bound to
63 a given trip point in this the 63 a given trip point in this thermal zone.
64 .get_temp: 64 .get_temp:
65 get the current temperature of 65 get the current temperature of the thermal zone.
66 .set_trips: 66 .set_trips:
67 set the trip points window. Wh 67 set the trip points window. Whenever the current temperature
68 is updated, the trip points im 68 is updated, the trip points immediately below and above the
69 current temperature are found. 69 current temperature are found.
70 .change_mode: 70 .change_mode:
71 change the mode (enabled/disab 71 change the mode (enabled/disabled) of the thermal zone.
72 .set_trip_temp: 72 .set_trip_temp:
73 set the temperature of a given 73 set the temperature of a given trip point.
74 .get_crit_temp: 74 .get_crit_temp:
75 get the critical temperature f 75 get the critical temperature for this thermal zone.
76 .set_emul_temp: 76 .set_emul_temp:
77 set the emulation temperature 77 set the emulation temperature which helps in debugging
78 different threshold temperatur 78 different threshold temperature points.
79 .get_trend: 79 .get_trend:
80 get the trend of most recent z 80 get the trend of most recent zone temperature changes.
81 .hot: 81 .hot:
82 hot trip point crossing handle 82 hot trip point crossing handler.
83 .critical: 83 .critical:
84 critical trip point crossing h 84 critical trip point crossing handler.
85 tzp: 85 tzp:
86 thermal zone platform parameters. 86 thermal zone platform parameters.
87 passive_delay: 87 passive_delay:
88 number of milliseconds to wait between 88 number of milliseconds to wait between polls when performing passive
89 cooling. 89 cooling.
90 polling_delay: 90 polling_delay:
91 number of milliseconds to wait between 91 number of milliseconds to wait between polls when checking
92 whether trip points have been crossed 92 whether trip points have been crossed (0 for interrupt driven systems).
93 93
94 :: 94 ::
95 95
96 void thermal_zone_device_unregister(st 96 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
97 97
98 This interface function removes the therma 98 This interface function removes the thermal zone device.
99 It deletes the corresponding entry from /s 99 It deletes the corresponding entry from /sys/class/thermal folder and
100 unbinds all the thermal cooling devices it 100 unbinds all the thermal cooling devices it uses.
101 101
102 :: 102 ::
103 103
104 struct thermal_zone_device 104 struct thermal_zone_device
105 *thermal_zone_of_sensor_register(st 105 *thermal_zone_of_sensor_register(struct device *dev, int sensor_id,
106 void *data, 106 void *data,
107 const struct t 107 const struct thermal_zone_of_device_ops *ops)
108 108
109 This interface adds a new sensor to a 109 This interface adds a new sensor to a DT thermal zone.
110 This function will search the list of 110 This function will search the list of thermal zones described in
111 device tree and look for the zone that 111 device tree and look for the zone that refer to the sensor device
112 pointed by dev->of_node as temperature 112 pointed by dev->of_node as temperature providers. For the zone
113 pointing to the sensor node, the senso 113 pointing to the sensor node, the sensor will be added to the DT
114 thermal zone device. 114 thermal zone device.
115 115
116 The parameters for this interface are: 116 The parameters for this interface are:
117 117
118 dev: 118 dev:
119 Device node of sensor 119 Device node of sensor containing valid node pointer in
120 dev->of_node. 120 dev->of_node.
121 sensor_id: 121 sensor_id:
122 a sensor identifier, i 122 a sensor identifier, in case the sensor IP has more
123 than one sensors 123 than one sensors
124 data: 124 data:
125 a private pointer (own 125 a private pointer (owned by the caller) that will be
126 passed back, when a te 126 passed back, when a temperature reading is needed.
127 ops: 127 ops:
128 `struct thermal_zone_o 128 `struct thermal_zone_of_device_ops *`.
129 129
130 ============== ====== 130 ============== =======================================
131 get_temp a poin 131 get_temp a pointer to a function that reads the
132 sensor 132 sensor temperature. This is mandatory
133 callba 133 callback provided by sensor driver.
134 set_trips a poin 134 set_trips a pointer to a function that sets a
135 temper 135 temperature window. When this window is
136 left t 136 left the driver must inform the thermal
137 core v 137 core via thermal_zone_device_update.
138 get_trend a poin 138 get_trend a pointer to a function that reads the
139 sensor 139 sensor temperature trend.
140 set_emul_temp a poin 140 set_emul_temp a pointer to a function that sets
141 sensor 141 sensor emulated temperature.
142 ============== ====== 142 ============== =======================================
143 143
144 The thermal zone temperature is provid 144 The thermal zone temperature is provided by the get_temp() function
145 pointer of thermal_zone_of_device_ops. 145 pointer of thermal_zone_of_device_ops. When called, it will
146 have the private pointer @data back. 146 have the private pointer @data back.
147 147
148 It returns error pointer if fails othe 148 It returns error pointer if fails otherwise valid thermal zone device
149 handle. Caller should check the return 149 handle. Caller should check the return handle with IS_ERR() for finding
150 whether success or not. 150 whether success or not.
151 151
152 :: 152 ::
153 153
154 void thermal_zone_of_sensor_unregi 154 void thermal_zone_of_sensor_unregister(struct device *dev,
155 155 struct thermal_zone_device *tzd)
156 156
157 This interface unregisters a sensor fr 157 This interface unregisters a sensor from a DT thermal zone which was
158 successfully added by interface therma 158 successfully added by interface thermal_zone_of_sensor_register().
159 This function removes the sensor callb 159 This function removes the sensor callbacks and private data from the
160 thermal zone device registered with th 160 thermal zone device registered with thermal_zone_of_sensor_register()
161 interface. It will also silent the zon 161 interface. It will also silent the zone by remove the .get_temp() and
162 get_trend() thermal zone device callba 162 get_trend() thermal zone device callbacks.
163 163
164 :: 164 ::
165 165
166 struct thermal_zone_device 166 struct thermal_zone_device
167 *devm_thermal_zone_of_sensor_registe 167 *devm_thermal_zone_of_sensor_register(struct device *dev,
168 int sensor_id, 168 int sensor_id,
169 void *data, 169 void *data,
170 const struct t 170 const struct thermal_zone_of_device_ops *ops)
171 171
172 This interface is resource managed ver 172 This interface is resource managed version of
173 thermal_zone_of_sensor_register(). 173 thermal_zone_of_sensor_register().
174 174
175 All details of thermal_zone_of_sensor_ 175 All details of thermal_zone_of_sensor_register() described in
176 section 1.1.3 is applicable here. 176 section 1.1.3 is applicable here.
177 177
178 The benefit of using this interface to 178 The benefit of using this interface to register sensor is that it
179 is not require to explicitly call ther 179 is not require to explicitly call thermal_zone_of_sensor_unregister()
180 in error path or during driver unbindi 180 in error path or during driver unbinding as this is done by driver
181 resource manager. 181 resource manager.
182 182
183 :: 183 ::
184 184
185 void devm_thermal_zone_of_sens 185 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
186 186 struct thermal_zone_device *tzd)
187 187
188 This interface is resource managed ver 188 This interface is resource managed version of
189 thermal_zone_of_sensor_unregister(). 189 thermal_zone_of_sensor_unregister().
190 All details of thermal_zone_of_sensor_ 190 All details of thermal_zone_of_sensor_unregister() described in
191 section 1.1.4 is applicable here. 191 section 1.1.4 is applicable here.
192 Normally this function will not need t 192 Normally this function will not need to be called and the resource
193 management code will ensure that the r 193 management code will ensure that the resource is freed.
194 194
195 :: 195 ::
196 196
197 int thermal_zone_get_slope(str 197 int thermal_zone_get_slope(struct thermal_zone_device *tz)
198 198
199 This interface is used to read the slo 199 This interface is used to read the slope attribute value
200 for the thermal zone device, which mig 200 for the thermal zone device, which might be useful for platform
201 drivers for temperature calculations. 201 drivers for temperature calculations.
202 202
203 :: 203 ::
204 204
205 int thermal_zone_get_offset(st 205 int thermal_zone_get_offset(struct thermal_zone_device *tz)
206 206
207 This interface is used to read the off 207 This interface is used to read the offset attribute value
208 for the thermal zone device, which mig 208 for the thermal zone device, which might be useful for platform
209 drivers for temperature calculations. 209 drivers for temperature calculations.
210 210
211 1.2 thermal cooling device interface 211 1.2 thermal cooling device interface
212 ------------------------------------ 212 ------------------------------------
213 213
214 214
215 :: 215 ::
216 216
217 struct thermal_cooling_device 217 struct thermal_cooling_device
218 *thermal_cooling_device_register(char 218 *thermal_cooling_device_register(char *name,
219 void *devdata, struct 219 void *devdata, struct thermal_cooling_device_ops *)
220 220
221 This interface function adds a new thermal 221 This interface function adds a new thermal cooling device (fan/processor/...)
222 to /sys/class/thermal/ folder as `cooling_ 222 to /sys/class/thermal/ folder as `cooling_device[0-*]`. It tries to bind itself
223 to all the thermal zone devices registered 223 to all the thermal zone devices registered at the same time.
224 224
225 name: 225 name:
226 the cooling device name. 226 the cooling device name.
227 devdata: 227 devdata:
228 device private data. 228 device private data.
229 ops: 229 ops:
230 thermal cooling devices call-backs. 230 thermal cooling devices call-backs.
231 231
232 .get_max_state: 232 .get_max_state:
233 get the Maximum throttle state 233 get the Maximum throttle state of the cooling device.
234 .get_cur_state: 234 .get_cur_state:
235 get the Currently requested th 235 get the Currently requested throttle state of the
236 cooling device. 236 cooling device.
237 .set_cur_state: 237 .set_cur_state:
238 set the Current throttle state 238 set the Current throttle state of the cooling device.
239 239
240 :: 240 ::
241 241
242 void thermal_cooling_device_unregister 242 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
243 243
244 This interface function removes the therma 244 This interface function removes the thermal cooling device.
245 It deletes the corresponding entry from /s 245 It deletes the corresponding entry from /sys/class/thermal folder and
246 unbinds itself from all the thermal zone d 246 unbinds itself from all the thermal zone devices using it.
247 247
248 1.4 Thermal Zone Parameters 248 1.4 Thermal Zone Parameters
249 --------------------------- 249 ---------------------------
250 250
251 :: 251 ::
252 252
253 struct thermal_zone_params 253 struct thermal_zone_params
254 254
255 This structure defines the platform level 255 This structure defines the platform level parameters for a thermal zone.
256 This data, for each thermal zone should co 256 This data, for each thermal zone should come from the platform layer.
257 This is an optional feature where some pla 257 This is an optional feature where some platforms can choose not to
258 provide this data. 258 provide this data.
259 259
260 .governor_name: 260 .governor_name:
261 Name of the thermal governor us 261 Name of the thermal governor used for this zone
262 .no_hwmon: 262 .no_hwmon:
263 a boolean to indicate if the th 263 a boolean to indicate if the thermal to hwmon sysfs interface
264 is required. when no_hwmon == f 264 is required. when no_hwmon == false, a hwmon sysfs interface
265 will be created. when no_hwmon 265 will be created. when no_hwmon == true, nothing will be done.
266 In case the thermal_zone_params 266 In case the thermal_zone_params is NULL, the hwmon interface
267 will be created (for backward c 267 will be created (for backward compatibility).
268 268
269 2. sysfs attributes structure 269 2. sysfs attributes structure
270 ============================= 270 =============================
271 271
272 == ================ 272 == ================
273 RO read only value 273 RO read only value
274 WO write only value 274 WO write only value
275 RW read/write value 275 RW read/write value
276 == ================ 276 == ================
277 277
278 Thermal sysfs attributes will be represented u 278 Thermal sysfs attributes will be represented under /sys/class/thermal.
279 Hwmon sysfs I/F extension is also available un 279 Hwmon sysfs I/F extension is also available under /sys/class/hwmon
280 if hwmon is compiled in or built as a module. 280 if hwmon is compiled in or built as a module.
281 281
282 Thermal zone device sys I/F, created once it's 282 Thermal zone device sys I/F, created once it's registered::
283 283
284 /sys/class/thermal/thermal_zone[0-*]: 284 /sys/class/thermal/thermal_zone[0-*]:
285 |---type: Type of the th 285 |---type: Type of the thermal zone
286 |---temp: Current temper 286 |---temp: Current temperature
287 |---mode: Working mode o 287 |---mode: Working mode of the thermal zone
288 |---policy: Thermal govern 288 |---policy: Thermal governor used for this zone
289 |---available_policies: Available ther 289 |---available_policies: Available thermal governors for this zone
290 |---trip_point_[0-*]_temp: Trip point tem 290 |---trip_point_[0-*]_temp: Trip point temperature
291 |---trip_point_[0-*]_type: Trip point typ 291 |---trip_point_[0-*]_type: Trip point type
292 |---trip_point_[0-*]_hyst: Hysteresis val 292 |---trip_point_[0-*]_hyst: Hysteresis value for this trip point
293 |---emul_temp: Emulated tempe 293 |---emul_temp: Emulated temperature set node
294 |---sustainable_power: Sustainable di 294 |---sustainable_power: Sustainable dissipatable power
295 |---k_po: Proportional t 295 |---k_po: Proportional term during temperature overshoot
296 |---k_pu: Proportional t 296 |---k_pu: Proportional term during temperature undershoot
297 |---k_i: PID's integral 297 |---k_i: PID's integral term in the power allocator gov
298 |---k_d: PID's derivati 298 |---k_d: PID's derivative term in the power allocator
299 |---integral_cutoff: Offset above w 299 |---integral_cutoff: Offset above which errors are accumulated
300 |---slope: Slope constant 300 |---slope: Slope constant applied as linear extrapolation
301 |---offset: Offset constan 301 |---offset: Offset constant applied as linear extrapolation
302 302
303 Thermal cooling device sys I/F, created once i 303 Thermal cooling device sys I/F, created once it's registered::
304 304
305 /sys/class/thermal/cooling_device[0-*]: 305 /sys/class/thermal/cooling_device[0-*]:
306 |---type: Type of the co 306 |---type: Type of the cooling device(processor/fan/...)
307 |---max_state: Maximum coolin 307 |---max_state: Maximum cooling state of the cooling device
308 |---cur_state: Current coolin 308 |---cur_state: Current cooling state of the cooling device
309 |---stats: Directory cont 309 |---stats: Directory containing cooling device's statistics
310 |---stats/reset: Writing any va 310 |---stats/reset: Writing any value resets the statistics
311 |---stats/time_in_state_ms: Time (msec) sp 311 |---stats/time_in_state_ms: Time (msec) spent in various cooling states
312 |---stats/total_trans: Total number o 312 |---stats/total_trans: Total number of times cooling state is changed
313 |---stats/trans_table: Cooling state 313 |---stats/trans_table: Cooling state transition table
314 314
315 315
316 Then next two dynamic attributes are created/r 316 Then next two dynamic attributes are created/removed in pairs. They represent
317 the relationship between a thermal zone and it 317 the relationship between a thermal zone and its associated cooling device.
318 318
319 :: 319 ::
320 320
321 /sys/class/thermal/thermal_zone[0-*]: 321 /sys/class/thermal/thermal_zone[0-*]:
322 |---cdev[0-*]: [0-*]th coolin 322 |---cdev[0-*]: [0-*]th cooling device in current thermal zone
323 |---cdev[0-*]_trip_point: Trip point tha 323 |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
324 |---cdev[0-*]_weight: Influence of t 324 |---cdev[0-*]_weight: Influence of the cooling device in
325 this thermal z 325 this thermal zone
326 326
327 Besides the thermal zone device sysfs I/F and 327 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
328 the generic thermal driver also creates a hwmo 328 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
329 of thermal zone device. E.g. the generic therm 329 of thermal zone device. E.g. the generic thermal driver registers one hwmon
330 class device and build the associated hwmon sy 330 class device and build the associated hwmon sysfs I/F for all the registered
331 ACPI thermal zones. 331 ACPI thermal zones.
332 332
333 Please read Documentation/ABI/testing/sysfs-cl 333 Please read Documentation/ABI/testing/sysfs-class-thermal for thermal
334 zone and cooling device attribute details. 334 zone and cooling device attribute details.
335 335
336 :: 336 ::
337 337
338 /sys/class/hwmon/hwmon[0-*]: 338 /sys/class/hwmon/hwmon[0-*]:
339 |---name: The type of th 339 |---name: The type of the thermal zone devices
340 |---temp[1-*]_input: The current te 340 |---temp[1-*]_input: The current temperature of thermal zone [1-*]
341 |---temp[1-*]_critical: The critical t 341 |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
342 342
343 Please read Documentation/hwmon/sysfs-interfac 343 Please read Documentation/hwmon/sysfs-interface.rst for additional information.
344 344
345 3. A simple implementation 345 3. A simple implementation
346 ========================== 346 ==========================
347 347
348 ACPI thermal zone may support multiple trip po 348 ACPI thermal zone may support multiple trip points like critical, hot,
349 passive, active. If an ACPI thermal zone suppo 349 passive, active. If an ACPI thermal zone supports critical, passive,
350 active[0] and active[1] at the same time, it m 350 active[0] and active[1] at the same time, it may register itself as a
351 thermal_zone_device (thermal_zone1) with 4 tri 351 thermal_zone_device (thermal_zone1) with 4 trip points in all.
352 It has one processor and one fan, which are bo 352 It has one processor and one fan, which are both registered as
353 thermal_cooling_device. Both are considered to 353 thermal_cooling_device. Both are considered to have the same
354 effectiveness in cooling the thermal zone. 354 effectiveness in cooling the thermal zone.
355 355
356 If the processor is listed in _PSL method, and 356 If the processor is listed in _PSL method, and the fan is listed in _AL0
357 method, the sys I/F structure will be built li 357 method, the sys I/F structure will be built like this::
358 358
359 /sys/class/thermal: 359 /sys/class/thermal:
360 |thermal_zone1: 360 |thermal_zone1:
361 |---type: acpitz 361 |---type: acpitz
362 |---temp: 37000 362 |---temp: 37000
363 |---mode: enabled 363 |---mode: enabled
364 |---policy: step_wise 364 |---policy: step_wise
365 |---available_policies: step_wise fair 365 |---available_policies: step_wise fair_share
366 |---trip_point_0_temp: 100000 366 |---trip_point_0_temp: 100000
367 |---trip_point_0_type: critical 367 |---trip_point_0_type: critical
368 |---trip_point_1_temp: 80000 368 |---trip_point_1_temp: 80000
369 |---trip_point_1_type: passive 369 |---trip_point_1_type: passive
370 |---trip_point_2_temp: 70000 370 |---trip_point_2_temp: 70000
371 |---trip_point_2_type: active0 371 |---trip_point_2_type: active0
372 |---trip_point_3_temp: 60000 372 |---trip_point_3_temp: 60000
373 |---trip_point_3_type: active1 373 |---trip_point_3_type: active1
374 |---cdev0: --->/sys/class 374 |---cdev0: --->/sys/class/thermal/cooling_device0
375 |---cdev0_trip_point: 1 /* cde 375 |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
376 |---cdev0_weight: 1024 376 |---cdev0_weight: 1024
377 |---cdev1: --->/sys/class 377 |---cdev1: --->/sys/class/thermal/cooling_device3
378 |---cdev1_trip_point: 2 /* cde 378 |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
379 |---cdev1_weight: 1024 379 |---cdev1_weight: 1024
380 380
381 |cooling_device0: 381 |cooling_device0:
382 |---type: Processor 382 |---type: Processor
383 |---max_state: 8 383 |---max_state: 8
384 |---cur_state: 0 384 |---cur_state: 0
385 385
386 |cooling_device3: 386 |cooling_device3:
387 |---type: Fan 387 |---type: Fan
388 |---max_state: 2 388 |---max_state: 2
389 |---cur_state: 0 389 |---cur_state: 0
390 390
391 /sys/class/hwmon: 391 /sys/class/hwmon:
392 |hwmon0: 392 |hwmon0:
393 |---name: acpitz 393 |---name: acpitz
394 |---temp1_input: 37000 394 |---temp1_input: 37000
395 |---temp1_crit: 100000 395 |---temp1_crit: 100000
396 396
397 4. Export Symbol APIs 397 4. Export Symbol APIs
398 ===================== 398 =====================
399 399
400 4.1. get_tz_trend 400 4.1. get_tz_trend
401 ----------------- 401 -----------------
402 402
403 This function returns the trend of a thermal z 403 This function returns the trend of a thermal zone, i.e the rate of change
404 of temperature of the thermal zone. Ideally, t 404 of temperature of the thermal zone. Ideally, the thermal sensor drivers
405 are supposed to implement the callback. If the 405 are supposed to implement the callback. If they don't, the thermal
406 framework calculated the trend by comparing th 406 framework calculated the trend by comparing the previous and the current
407 temperature values. 407 temperature values.
408 408
409 4.2. thermal_cdev_update 409 4.2. thermal_cdev_update
410 ------------------------ 410 ------------------------
411 411
412 This function serves as an arbitrator to set t 412 This function serves as an arbitrator to set the state of a cooling
413 device. It sets the cooling device to the deep 413 device. It sets the cooling device to the deepest cooling state if
414 possible. 414 possible.
415 415
416 5. thermal_emergency_poweroff 416 5. thermal_emergency_poweroff
417 ============================= 417 =============================
418 418
419 On an event of critical trip temperature cross 419 On an event of critical trip temperature crossing the thermal framework
420 shuts down the system by calling hw_protection 420 shuts down the system by calling hw_protection_shutdown(). The
421 hw_protection_shutdown() first attempts to per 421 hw_protection_shutdown() first attempts to perform an orderly shutdown
422 but accepts a delay after which it proceeds do 422 but accepts a delay after which it proceeds doing a forced power-off
423 or as last resort an emergency_restart. 423 or as last resort an emergency_restart.
424 424
425 The delay should be carefully profiled so as t 425 The delay should be carefully profiled so as to give adequate time for
426 orderly poweroff. 426 orderly poweroff.
427 427
428 If the delay is set to 0 emergency poweroff wi 428 If the delay is set to 0 emergency poweroff will not be supported. So a
429 carefully profiled non-zero positive value is 429 carefully profiled non-zero positive value is a must for emergency
430 poweroff to be triggered. 430 poweroff to be triggered.
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