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2 Generic Thermal Sysfs driver How To
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5 Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
7 Updated: 2 January 2008
9 Copyright (c) 2008 Intel Corporation
15 The generic thermal sysfs provides a set of interfaces for thermal zone
16 devices (sensors) and thermal cooling devices (fan, processor...) to register
17 with the thermal management solution and to be a part of it.
19 This how-to focuses on enabling new thermal zone and cooling devices to
20 participate in thermal management.
21 This solution is platform independent and any type of thermal zone devices
22 and cooling devices should be able to make use of the infrastructure.
24 The main task of the thermal sysfs driver is to expose thermal zone attributes
25 as well as cooling device attributes to the user space.
26 An intelligent thermal management application can make decisions based on
27 inputs from thermal zone attributes (the current temperature and trip point
28 temperature) and throttle appropriate devices.
30 - `[0-*]` denotes any positive number starting from 0
31 - `[1-*]` denotes any positive number starting from 1
33 1. thermal sysfs driver interface functions
34 ===========================================
36 1.1 thermal zone device interface
37 ---------------------------------
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))
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.
53 the thermal zone type.
55 the total number of trip points this thermal zone supports.
57 Bit string: If 'n'th bit is set, then trip point 'n' is writable.
61 thermal zone device call-backs.
64 bind the thermal zone device with a thermal cooling device.
66 unbind the thermal zone device with a thermal cooling device.
68 get the current temperature of the thermal zone.
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.
74 get the current mode (enabled/disabled) of the thermal zone.
76 - "enabled" means the kernel thermal management is
78 - "disabled" will prevent kernel thermal driver action
79 upon trip points so that user applications can take
80 charge of thermal management.
82 set the mode (enabled/disabled) of the thermal zone.
84 get the type of certain trip point.
86 get the temperature above which the certain trip point
89 set the emulation temperature which helps in debugging
90 different threshold temperature points.
92 thermal zone platform parameters.
94 number of milliseconds to wait between polls when
95 performing passive cooling.
97 number of milliseconds to wait between polls when checking
98 whether trip points have been crossed (0 for interrupt driven systems).
102 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
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.
110 struct thermal_zone_device
111 *thermal_zone_of_sensor_register(struct device *dev, int sensor_id,
113 const struct thermal_zone_of_device_ops *ops)
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
122 The parameters for this interface are:
125 Device node of sensor containing valid node pointer in
128 a sensor identifier, in case the sensor IP has more
131 a private pointer (owned by the caller) that will be
132 passed back, when a temperature reading is needed.
134 `struct thermal_zone_of_device_ops *`.
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 ============== =======================================
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.
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.
160 void thermal_zone_of_sensor_unregister(struct device *dev,
161 struct thermal_zone_device *tzd)
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.
172 struct thermal_zone_device
173 *devm_thermal_zone_of_sensor_register(struct device *dev,
176 const struct thermal_zone_of_device_ops *ops)
178 This interface is resource managed version of
179 thermal_zone_of_sensor_register().
181 All details of thermal_zone_of_sensor_register() described in
182 section 1.1.3 is applicable here.
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
191 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
192 struct thermal_zone_device *tzd)
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.
203 int thermal_zone_get_slope(struct thermal_zone_device *tz)
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.
211 int thermal_zone_get_offset(struct thermal_zone_device *tz)
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.
217 1.2 thermal cooling device interface
218 ------------------------------------
223 struct thermal_cooling_device
224 *thermal_cooling_device_register(char *name,
225 void *devdata, struct thermal_cooling_device_ops *)
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.
232 the cooling device name.
236 thermal cooling devices call-backs.
239 get the Maximum throttle state of the cooling device.
241 get the Currently requested throttle state of the
244 set the Current throttle state of the cooling device.
248 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
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.
254 1.3 interface for binding a thermal zone device with a thermal cooling device
255 -----------------------------------------------------------------------------
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);
263 This interface function binds a thermal cooling device to a particular trip
264 point of a thermal zone device.
266 This function is usually called in the thermal zone device .bind callback.
269 the thermal zone device
271 thermal cooling device
273 indicates which trip point in this thermal zone the cooling device
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.
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.
284 the influence of this cooling device in this thermal
285 zone. See 1.4.1 below for more information.
289 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
290 int trip, struct thermal_cooling_device *cdev);
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.
297 the thermal zone device
299 thermal cooling device
301 indicates which trip point in this thermal zone the cooling device
304 1.4 Thermal Zone Parameters
305 ---------------------------
309 struct thermal_zone_params
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
317 Name of the thermal governor used for this zone
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).
325 2. sysfs attributes structure
326 =============================
334 Thermal sysfs attributes will be represented under /sys/class/thermal.
335 Hwmon sysfs I/F extension is also available under /sys/class/hwmon
336 if hwmon is compiled in or built as a module.
338 Thermal zone device sys I/F, created once it's registered::
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
359 Thermal cooling device sys I/F, created once it's registered::
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
372 Then next two dynamic attributes are created/removed in pairs. They represent
373 the relationship between a thermal zone and its associated cooling device.
374 They are created/removed for each successful execution of
375 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
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
385 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
386 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
387 of thermal zone device. E.g. the generic thermal driver registers one hwmon
388 class device and build the associated hwmon sysfs I/F for all the registered
391 Please read Documentation/ABI/testing/sysfs-class-thermal for thermal
392 zone and cooling device attribute details.
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-*]
401 Please read Documentation/hwmon/sysfs-interface.rst for additional information.
403 3. A simple implementation
404 ==========================
406 ACPI thermal zone may support multiple trip points like critical, hot,
407 passive, active. If an ACPI thermal zone supports critical, passive,
408 active[0] and active[1] at the same time, it may register itself as a
409 thermal_zone_device (thermal_zone1) with 4 trip points in all.
410 It has one processor and one fan, which are both registered as
411 thermal_cooling_device. Both are considered to have the same
412 effectiveness in cooling the thermal zone.
414 If the processor is listed in _PSL method, and the fan is listed in _AL0
415 method, the sys I/F structure will be built like this::
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
452 |---temp1_input: 37000
453 |---temp1_crit: 100000
455 4. Export Symbol APIs
456 =====================
461 This function returns the trend of a thermal zone, i.e the rate of change
462 of temperature of the thermal zone. Ideally, the thermal sensor drivers
463 are supposed to implement the callback. If they don't, the thermal
464 framework calculated the trend by comparing the previous and the current
467 4.2. get_thermal_instance
468 -------------------------
470 This function returns the thermal_instance corresponding to a given
471 {thermal_zone, cooling_device, trip_point} combination. Returns NULL
472 if such an instance does not exist.
474 4.3. thermal_cdev_update
475 ------------------------
477 This function serves as an arbitrator to set the state of a cooling
478 device. It sets the cooling device to the deepest cooling state if
481 5. thermal_emergency_poweroff
482 =============================
484 On an event of critical trip temperature crossing the thermal framework
485 shuts down the system by calling hw_protection_shutdown(). The
486 hw_protection_shutdown() first attempts to perform an orderly shutdown
487 but accepts a delay after which it proceeds doing a forced power-off
488 or as last resort an emergency_restart.
490 The delay should be carefully profiled so as to give adequate time for
493 If the delay is set to 0 emergency poweroff will not be supported. So a
494 carefully profiled non-zero positive value is a must for emergency
495 poweroff to be triggered.