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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_bind_params
310
311 This structure defines the following parameters that are used to bind
312 a zone with a cooling device for a particular trip point.
313
314 .cdev:
315 The cooling device pointer
316 .weight:
317 The 'influence' of a particular cooling device on this
318 zone. This is relative to the rest of the cooling
319 devices. For example, if all cooling devices have a
320 weight of 1, then they all contribute the same. You can
321 use percentages if you want, but it's not mandatory. A
322 weight of 0 means that this cooling device doesn't
323 contribute to the cooling of this zone unless all cooling
324 devices have a weight of 0. If all weights are 0, then
325 they all contribute the same.
326 .trip_mask:
327 This is a bit mask that gives the binding relation between
328 this thermal zone and cdev, for a particular trip point.
329 If nth bit is set, then the cdev and thermal zone are bound
330 for trip point n.
331 .binding_limits:
332 This is an array of cooling state limits. Must have
333 exactly 2 * thermal_zone.number_of_trip_points. It is an
334 array consisting of tuples <lower-state upper-state> of
335 state limits. Each trip will be associated with one state
336 limit tuple when binding. A NULL pointer means
337 <THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips.
338 These limits are used when binding a cdev to a trip point.
339 .match:
340 This call back returns success(0) if the 'tz and cdev' need to
341 be bound, as per platform data.
342
343 ::
344
345 struct thermal_zone_params
346
347 This structure defines the platform level parameters for a thermal zone.
348 This data, for each thermal zone should come from the platform layer.
349 This is an optional feature where some platforms can choose not to
350 provide this data.
351
352 .governor_name:
353 Name of the thermal governor used for this zone
354 .no_hwmon:
355 a boolean to indicate if the thermal to hwmon sysfs interface
356 is required. when no_hwmon == false, a hwmon sysfs interface
357 will be created. when no_hwmon == true, nothing will be done.
358 In case the thermal_zone_params is NULL, the hwmon interface
359 will be created (for backward compatibility).
360 .num_tbps:
361 Number of thermal_bind_params entries for this zone
362 .tbp:
363 thermal_bind_params entries
364
3652. sysfs attributes structure
366=============================
367
368== ================
369RO read only value
370WO write only value
371RW read/write value
372== ================
373
374Thermal sysfs attributes will be represented under /sys/class/thermal.
375Hwmon sysfs I/F extension is also available under /sys/class/hwmon
376if hwmon is compiled in or built as a module.
377
378Thermal zone device sys I/F, created once it's registered::
379
380 /sys/class/thermal/thermal_zone[0-*]:
381 |---type: Type of the thermal zone
382 |---temp: Current temperature
383 |---mode: Working mode of the thermal zone
384 |---policy: Thermal governor used for this zone
385 |---available_policies: Available thermal governors for this zone
386 |---trip_point_[0-*]_temp: Trip point temperature
387 |---trip_point_[0-*]_type: Trip point type
388 |---trip_point_[0-*]_hyst: Hysteresis value for this trip point
389 |---emul_temp: Emulated temperature set node
390 |---sustainable_power: Sustainable dissipatable power
391 |---k_po: Proportional term during temperature overshoot
392 |---k_pu: Proportional term during temperature undershoot
393 |---k_i: PID's integral term in the power allocator gov
394 |---k_d: PID's derivative term in the power allocator
395 |---integral_cutoff: Offset above which errors are accumulated
396 |---slope: Slope constant applied as linear extrapolation
397 |---offset: Offset constant applied as linear extrapolation
398
399Thermal cooling device sys I/F, created once it's registered::
400
401 /sys/class/thermal/cooling_device[0-*]:
402 |---type: Type of the cooling device(processor/fan/...)
403 |---max_state: Maximum cooling state of the cooling device
404 |---cur_state: Current cooling state of the cooling device
405 |---stats: Directory containing cooling device's statistics
406 |---stats/reset: Writing any value resets the statistics
407 |---stats/time_in_state_ms: Time (msec) spent in various cooling states
408 |---stats/total_trans: Total number of times cooling state is changed
409 |---stats/trans_table: Cooling state transition table
410
411
412Then next two dynamic attributes are created/removed in pairs. They represent
413the relationship between a thermal zone and its associated cooling device.
414They are created/removed for each successful execution of
415thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
416
417::
418
419 /sys/class/thermal/thermal_zone[0-*]:
420 |---cdev[0-*]: [0-*]th cooling device in current thermal zone
421 |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
422 |---cdev[0-*]_weight: Influence of the cooling device in
423 this thermal zone
424
425Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
426the generic thermal driver also creates a hwmon sysfs I/F for each _type_
427of thermal zone device. E.g. the generic thermal driver registers one hwmon
428class device and build the associated hwmon sysfs I/F for all the registered
429ACPI thermal zones.
430
431Please read Documentation/ABI/testing/sysfs-class-thermal for thermal
432zone and cooling device attribute details.
433
434::
435
436 /sys/class/hwmon/hwmon[0-*]:
437 |---name: The type of the thermal zone devices
438 |---temp[1-*]_input: The current temperature of thermal zone [1-*]
439 |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
440
441Please read Documentation/hwmon/sysfs-interface.rst for additional information.
442
4433. A simple implementation
444==========================
445
446ACPI thermal zone may support multiple trip points like critical, hot,
447passive, active. If an ACPI thermal zone supports critical, passive,
448active[0] and active[1] at the same time, it may register itself as a
449thermal_zone_device (thermal_zone1) with 4 trip points in all.
450It has one processor and one fan, which are both registered as
451thermal_cooling_device. Both are considered to have the same
452effectiveness in cooling the thermal zone.
453
454If the processor is listed in _PSL method, and the fan is listed in _AL0
455method, the sys I/F structure will be built like this::
456
457 /sys/class/thermal:
458 |thermal_zone1:
459 |---type: acpitz
460 |---temp: 37000
461 |---mode: enabled
462 |---policy: step_wise
463 |---available_policies: step_wise fair_share
464 |---trip_point_0_temp: 100000
465 |---trip_point_0_type: critical
466 |---trip_point_1_temp: 80000
467 |---trip_point_1_type: passive
468 |---trip_point_2_temp: 70000
469 |---trip_point_2_type: active0
470 |---trip_point_3_temp: 60000
471 |---trip_point_3_type: active1
472 |---cdev0: --->/sys/class/thermal/cooling_device0
473 |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
474 |---cdev0_weight: 1024
475 |---cdev1: --->/sys/class/thermal/cooling_device3
476 |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
477 |---cdev1_weight: 1024
478
479 |cooling_device0:
480 |---type: Processor
481 |---max_state: 8
482 |---cur_state: 0
483
484 |cooling_device3:
485 |---type: Fan
486 |---max_state: 2
487 |---cur_state: 0
488
489 /sys/class/hwmon:
490 |hwmon0:
491 |---name: acpitz
492 |---temp1_input: 37000
493 |---temp1_crit: 100000
494
4954. Export Symbol APIs
496=====================
497
4984.1. get_tz_trend
499-----------------
500
501This function returns the trend of a thermal zone, i.e the rate of change
502of temperature of the thermal zone. Ideally, the thermal sensor drivers
503are supposed to implement the callback. If they don't, the thermal
504framework calculated the trend by comparing the previous and the current
505temperature values.
506
5074.2. get_thermal_instance
508-------------------------
509
510This function returns the thermal_instance corresponding to a given
511{thermal_zone, cooling_device, trip_point} combination. Returns NULL
512if such an instance does not exist.
513
5144.3. thermal_cdev_update
515------------------------
516
517This function serves as an arbitrator to set the state of a cooling
518device. It sets the cooling device to the deepest cooling state if
519possible.
520
5215. thermal_emergency_poweroff
522=============================
523
524On an event of critical trip temperature crossing the thermal framework
525shuts down the system by calling hw_protection_shutdown(). The
526hw_protection_shutdown() first attempts to perform an orderly shutdown
527but accepts a delay after which it proceeds doing a forced power-off
528or as last resort an emergency_restart.
529
530The delay should be carefully profiled so as to give adequate time for
531orderly poweroff.
532
533If the delay is set to 0 emergency poweroff will not be supported. So a
534carefully profiled non-zero positive value is a must for emergency
535poweroff to be triggered.