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Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.

1	Generic Thermal Sysfs driver How To
2	===================================
4	Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
6	Updated: 2 January 2008
8	Copyright (c)  2008 Intel Corporation
11	0. Introduction
13	The generic thermal sysfs provides a set of interfaces for thermal zone
14	devices (sensors) and thermal cooling devices (fan, processor...) to register
15	with the thermal management solution and to be a part of it.
17	This how-to focuses on enabling new thermal zone and cooling devices to
18	participate in thermal management.
19	This solution is platform independent and any type of thermal zone devices
20	and cooling devices should be able to make use of the infrastructure.
22	The main task of the thermal sysfs driver is to expose thermal zone attributes
23	as well as cooling device attributes to the user space.
24	An intelligent thermal management application can make decisions based on
25	inputs from thermal zone attributes (the current temperature and trip point
26	temperature) and throttle appropriate devices.
28	[0-*]	denotes any positive number starting from 0
29	[1-*]	denotes any positive number starting from 1
31	1. thermal sysfs driver interface functions
33	1.1 thermal zone device interface
34	1.1.1 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))
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.
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).
69	1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
71	    This interface function removes the thermal zone device.
72	    It deletes the corresponding entry from /sys/class/thermal folder and
73	    unbinds all the thermal cooling devices it uses.
75	1.1.3 struct thermal_zone_device *thermal_zone_of_sensor_register(
76			struct device *dev, int sensor_id, void *data,
77			const struct thermal_zone_of_device_ops *ops)
79		This interface adds a new sensor to a DT thermal zone.
80		This function will search the list of thermal zones described in
81		device tree and look for the zone that refer to the sensor device
82		pointed by dev->of_node as temperature providers. For the zone
83		pointing to the sensor node, the sensor will be added to the DT
84		thermal zone device.
86		The parameters for this interface are:
87		dev:		Device node of sensor containing valid node pointer in
88				dev->of_node.
89		sensor_id:	a sensor identifier, in case the sensor IP has more
90				than one sensors
91		data:		a private pointer (owned by the caller) that will be
92				passed back, when a temperature reading is needed.
93		ops:		struct thermal_zone_of_device_ops *.
95				get_temp:	a pointer to a function that reads the
96						sensor temperature. This is mandatory
97						callback provided by sensor driver.
98				get_trend: 	a pointer to a function that reads the
99						sensor temperature trend.
100				set_emul_temp:	a pointer to a function that sets
101						sensor emulated temperature.
102		The thermal zone temperature is provided by the get_temp() function
103		pointer of thermal_zone_of_device_ops. When called, it will
104		have the private pointer @data back.
106		It returns error pointer if fails otherwise valid thermal zone device
107		handle. Caller should check the return handle with IS_ERR() for finding
108		whether success or not.
110	1.1.4 void thermal_zone_of_sensor_unregister(struct device *dev,
111			struct thermal_zone_device *tzd)
113		This interface unregisters a sensor from a DT thermal zone which was
114		successfully added by interface thermal_zone_of_sensor_register().
115		This function removes the sensor callbacks and private data from the
116		thermal zone device registered with thermal_zone_of_sensor_register()
117		interface. It will also silent the zone by remove the .get_temp() and
118		get_trend() thermal zone device callbacks.
120	1.1.5 struct thermal_zone_device *devm_thermal_zone_of_sensor_register(
121			struct device *dev, int sensor_id,
122			void *data, const struct thermal_zone_of_device_ops *ops)
124		This interface is resource managed version of
125		thermal_zone_of_sensor_register().
126		All details of thermal_zone_of_sensor_register() described in
127		section 1.1.3 is applicable here.
128		The benefit of using this interface to register sensor is that it
129		is not require to explicitly call thermal_zone_of_sensor_unregister()
130		in error path or during driver unbinding as this is done by driver
131		resource manager.
133	1.1.6 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
134			struct thermal_zone_device *tzd)
136		This interface is resource managed version of
137		thermal_zone_of_sensor_unregister().
138		All details of thermal_zone_of_sensor_unregister() described in
139		section 1.1.4 is applicable here.
140		Normally this function will not need to be called and the resource
141		management code will ensure that the resource is freed.
143	1.2 thermal cooling device interface
144	1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
145			void *devdata, struct thermal_cooling_device_ops *)
147	    This interface function adds a new thermal cooling device (fan/processor/...)
148	    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
149	    to all the thermal zone devices registered at the same time.
150	    name: the cooling device name.
151	    devdata: device private data.
152	    ops: thermal cooling devices call-backs.
153		.get_max_state: get the Maximum throttle state of the cooling device.
154		.get_cur_state: get the Currently requested throttle state of the cooling device.
155		.set_cur_state: set the Current throttle state of the cooling device.
157	1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
159	    This interface function removes the thermal cooling device.
160	    It deletes the corresponding entry from /sys/class/thermal folder and
161	    unbinds itself from all the thermal zone devices using it.
163	1.3 interface for binding a thermal zone device with a thermal cooling device
164	1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
165		int trip, struct thermal_cooling_device *cdev,
166		unsigned long upper, unsigned long lower, unsigned int weight);
168	    This interface function binds a thermal cooling device to a particular trip
169	    point of a thermal zone device.
170	    This function is usually called in the thermal zone device .bind callback.
171	    tz: the thermal zone device
172	    cdev: thermal cooling device
173	    trip: indicates which trip point in this thermal zone the cooling device
174	          is associated with.
175	    upper:the Maximum cooling state for this trip point.
176	          THERMAL_NO_LIMIT means no upper limit,
177		  and the cooling device can be in max_state.
178	    lower:the Minimum cooling state can be used for this trip point.
179	          THERMAL_NO_LIMIT means no lower limit,
180		  and the cooling device can be in cooling state 0.
181	    weight: the influence of this cooling device in this thermal
182	            zone.  See 1.4.1 below for more information.
184	1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
185			int trip, struct thermal_cooling_device *cdev);
187	    This interface function unbinds a thermal cooling device from a particular
188	    trip point of a thermal zone device. This function is usually called in
189	    the thermal zone device .unbind callback.
190	    tz: the thermal zone device
191	    cdev: thermal cooling device
192	    trip: indicates which trip point in this thermal zone the cooling device
193	          is associated with.
195	1.4 Thermal Zone Parameters
196	1.4.1 struct thermal_bind_params
197	    This structure defines the following parameters that are used to bind
198	    a zone with a cooling device for a particular trip point.
199	    .cdev: The cooling device pointer
200	    .weight: The 'influence' of a particular cooling device on this
201	             zone. This is relative to the rest of the cooling
202	             devices. For example, if all cooling devices have a
203	             weight of 1, then they all contribute the same. You can
204	             use percentages if you want, but it's not mandatory. A
205	             weight of 0 means that this cooling device doesn't
206	             contribute to the cooling of this zone unless all cooling
207	             devices have a weight of 0. If all weights are 0, then
208	             they all contribute the same.
209	    .trip_mask:This is a bit mask that gives the binding relation between
210	               this thermal zone and cdev, for a particular trip point.
211	               If nth bit is set, then the cdev and thermal zone are bound
212	               for trip point n.
213	    .binding_limits: This is an array of cooling state limits. Must have
214	                     exactly 2 * thermal_zone.number_of_trip_points. It is an
215	                     array consisting of tuples <lower-state upper-state> of
216	                     state limits. Each trip will be associated with one state
217	                     limit tuple when binding. A NULL pointer means
218	                     <THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips.
219	                     These limits are used when binding a cdev to a trip point.
220	    .match: This call back returns success(0) if the 'tz and cdev' need to
221		    be bound, as per platform data.
222	1.4.2 struct thermal_zone_params
223	    This structure defines the platform level parameters for a thermal zone.
224	    This data, for each thermal zone should come from the platform layer.
225	    This is an optional feature where some platforms can choose not to
226	    provide this data.
227	    .governor_name: Name of the thermal governor used for this zone
228	    .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
229	               is required. when no_hwmon == false, a hwmon sysfs interface
230	               will be created. when no_hwmon == true, nothing will be done.
231	               In case the thermal_zone_params is NULL, the hwmon interface
232	               will be created (for backward compatibility).
233	    .num_tbps: Number of thermal_bind_params entries for this zone
234	    .tbp: thermal_bind_params entries
236	2. sysfs attributes structure
238	RO	read only value
239	RW	read/write value
241	Thermal sysfs attributes will be represented under /sys/class/thermal.
242	Hwmon sysfs I/F extension is also available under /sys/class/hwmon
243	if hwmon is compiled in or built as a module.
245	Thermal zone device sys I/F, created once it's registered:
246	/sys/class/thermal/thermal_zone[0-*]:
247	    |---type:			Type of the thermal zone
248	    |---temp:			Current temperature
249	    |---mode:			Working mode of the thermal zone
250	    |---policy:			Thermal governor used for this zone
251	    |---available_policies:	Available thermal governors for this zone
252	    |---trip_point_[0-*]_temp:	Trip point temperature
253	    |---trip_point_[0-*]_type:	Trip point type
254	    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point
255	    |---emul_temp:		Emulated temperature set node
256	    |---sustainable_power:      Sustainable dissipatable power
257	    |---k_po:                   Proportional term during temperature overshoot
258	    |---k_pu:                   Proportional term during temperature undershoot
259	    |---k_i:                    PID's integral term in the power allocator gov
260	    |---k_d:                    PID's derivative term in the power allocator
261	    |---integral_cutoff:        Offset above which errors are accumulated
262	    |---slope:                  Slope constant applied as linear extrapolation
263	    |---offset:                 Offset constant applied as linear extrapolation
265	Thermal cooling device sys I/F, created once it's registered:
266	/sys/class/thermal/cooling_device[0-*]:
267	    |---type:			Type of the cooling device(processor/fan/...)
268	    |---max_state:		Maximum cooling state of the cooling device
269	    |---cur_state:		Current cooling state of the cooling device
272	Then next two dynamic attributes are created/removed in pairs. They represent
273	the relationship between a thermal zone and its associated cooling device.
274	They are created/removed for each successful execution of
275	thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
277	/sys/class/thermal/thermal_zone[0-*]:
278	    |---cdev[0-*]:		[0-*]th cooling device in current thermal zone
279	    |---cdev[0-*]_trip_point:	Trip point that cdev[0-*] is associated with
280	    |---cdev[0-*]_weight:       Influence of the cooling device in
281	                                this thermal zone
283	Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
284	the generic thermal driver also creates a hwmon sysfs I/F for each _type_
285	of thermal zone device. E.g. the generic thermal driver registers one hwmon
286	class device and build the associated hwmon sysfs I/F for all the registered
287	ACPI thermal zones.
289	/sys/class/hwmon/hwmon[0-*]:
290	    |---name:			The type of the thermal zone devices
291	    |---temp[1-*]_input:	The current temperature of thermal zone [1-*]
292	    |---temp[1-*]_critical:	The critical trip point of thermal zone [1-*]
294	Please read Documentation/hwmon/sysfs-interface for additional information.
296	***************************
297	* Thermal zone attributes *
298	***************************
300	type
301		Strings which represent the thermal zone type.
302		This is given by thermal zone driver as part of registration.
303		E.g: "acpitz" indicates it's an ACPI thermal device.
304		In order to keep it consistent with hwmon sys attribute; this should
305		be a short, lowercase string, not containing spaces nor dashes.
306		RO, Required
308	temp
309		Current temperature as reported by thermal zone (sensor).
310		Unit: millidegree Celsius
311		RO, Required
313	mode
314		One of the predefined values in [enabled, disabled].
315		This file gives information about the algorithm that is currently
316		managing the thermal zone. It can be either default kernel based
317		algorithm or user space application.
318		enabled		= enable Kernel Thermal management.
319		disabled	= Preventing kernel thermal zone driver actions upon
320				  trip points so that user application can take full
321				  charge of the thermal management.
322		RW, Optional
324	policy
325		One of the various thermal governors used for a particular zone.
326		RW, Required
328	available_policies
329		Available thermal governors which can be used for a particular zone.
330		RO, Required
332	trip_point_[0-*]_temp
333		The temperature above which trip point will be fired.
334		Unit: millidegree Celsius
335		RO, Optional
337	trip_point_[0-*]_type
338		Strings which indicate the type of the trip point.
339		E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
340		thermal zone.
341		RO, Optional
343	trip_point_[0-*]_hyst
344		The hysteresis value for a trip point, represented as an integer
345		Unit: Celsius
346		RW, Optional
348	cdev[0-*]
349		Sysfs link to the thermal cooling device node where the sys I/F
350		for cooling device throttling control represents.
351		RO, Optional
353	cdev[0-*]_trip_point
354		The trip point in this thermal zone which cdev[0-*] is associated
355		with; -1 means the cooling device is not associated with any trip
356		point.
357		RO, Optional
359	cdev[0-*]_weight
360	        The influence of cdev[0-*] in this thermal zone. This value
361	        is relative to the rest of cooling devices in the thermal
362	        zone. For example, if a cooling device has a weight double
363	        than that of other, it's twice as effective in cooling the
364	        thermal zone.
365	        RW, Optional
367	passive
368		Attribute is only present for zones in which the passive cooling
369		policy is not supported by native thermal driver. Default is zero
370		and can be set to a temperature (in millidegrees) to enable a
371		passive trip point for the zone. Activation is done by polling with
372		an interval of 1 second.
373		Unit: millidegrees Celsius
374		Valid values: 0 (disabled) or greater than 1000
375		RW, Optional
377	emul_temp
378		Interface to set the emulated temperature method in thermal zone
379		(sensor). After setting this temperature, the thermal zone may pass
380		this temperature to platform emulation function if registered or
381		cache it locally. This is useful in debugging different temperature
382		threshold and its associated cooling action. This is write only node
383		and writing 0 on this node should disable emulation.
384		Unit: millidegree Celsius
385		WO, Optional
387		  WARNING: Be careful while enabling this option on production systems,
388		  because userland can easily disable the thermal policy by simply
389		  flooding this sysfs node with low temperature values.
391	sustainable_power
392		An estimate of the sustained power that can be dissipated by
393		the thermal zone. Used by the power allocator governor. For
394		more information see Documentation/thermal/power_allocator.txt
395		Unit: milliwatts
396		RW, Optional
398	k_po
399		The proportional term of the power allocator governor's PID
400		controller during temperature overshoot. Temperature overshoot
401		is when the current temperature is above the "desired
402		temperature" trip point. For more information see
403		Documentation/thermal/power_allocator.txt
404		RW, Optional
406	k_pu
407		The proportional term of the power allocator governor's PID
408		controller during temperature undershoot. Temperature undershoot
409		is when the current temperature is below the "desired
410		temperature" trip point. For more information see
411		Documentation/thermal/power_allocator.txt
412		RW, Optional
414	k_i
415		The integral term of the power allocator governor's PID
416		controller. This term allows the PID controller to compensate
417		for long term drift. For more information see
418		Documentation/thermal/power_allocator.txt
419		RW, Optional
421	k_d
422		The derivative term of the power allocator governor's PID
423		controller. For more information see
424		Documentation/thermal/power_allocator.txt
425		RW, Optional
427	integral_cutoff
428		Temperature offset from the desired temperature trip point
429		above which the integral term of the power allocator
430		governor's PID controller starts accumulating errors. For
431		example, if integral_cutoff is 0, then the integral term only
432		accumulates error when temperature is above the desired
433		temperature trip point. For more information see
434		Documentation/thermal/power_allocator.txt
435		Unit: millidegree Celsius
436		RW, Optional
438	slope
439		The slope constant used in a linear extrapolation model
440		to determine a hotspot temperature based off the sensor's
441		raw readings. It is up to the device driver to determine
442		the usage of these values.
443		RW, Optional
445	offset
446		The offset constant used in a linear extrapolation model
447		to determine a hotspot temperature based off the sensor's
448		raw readings. It is up to the device driver to determine
449		the usage of these values.
450		RW, Optional
452	*****************************
453	* Cooling device attributes *
454	*****************************
456	type
457		String which represents the type of device, e.g:
458		- for generic ACPI: should be "Fan", "Processor" or "LCD"
459		- for memory controller device on intel_menlow platform:
460		  should be "Memory controller".
461		RO, Required
463	max_state
464		The maximum permissible cooling state of this cooling device.
465		RO, Required
467	cur_state
468		The current cooling state of this cooling device.
469		The value can any integer numbers between 0 and max_state:
470		- cur_state == 0 means no cooling
471		- cur_state == max_state means the maximum cooling.
472		RW, Required
474	3. A simple implementation
476	ACPI thermal zone may support multiple trip points like critical, hot,
477	passive, active. If an ACPI thermal zone supports critical, passive,
478	active[0] and active[1] at the same time, it may register itself as a
479	thermal_zone_device (thermal_zone1) with 4 trip points in all.
480	It has one processor and one fan, which are both registered as
481	thermal_cooling_device. Both are considered to have the same
482	effectiveness in cooling the thermal zone.
484	If the processor is listed in _PSL method, and the fan is listed in _AL0
485	method, the sys I/F structure will be built like this:
487	/sys/class/thermal:
489	|thermal_zone1:
490	    |---type:			acpitz
491	    |---temp:			37000
492	    |---mode:			enabled
493	    |---policy:			step_wise
494	    |---available_policies:	step_wise fair_share
495	    |---trip_point_0_temp:	100000
496	    |---trip_point_0_type:	critical
497	    |---trip_point_1_temp:	80000
498	    |---trip_point_1_type:	passive
499	    |---trip_point_2_temp:	70000
500	    |---trip_point_2_type:	active0
501	    |---trip_point_3_temp:	60000
502	    |---trip_point_3_type:	active1
503	    |---cdev0:			--->/sys/class/thermal/cooling_device0
504	    |---cdev0_trip_point:	1	/* cdev0 can be used for passive */
505	    |---cdev0_weight:           1024
506	    |---cdev1:			--->/sys/class/thermal/cooling_device3
507	    |---cdev1_trip_point:	2	/* cdev1 can be used for active[0]*/
508	    |---cdev1_weight:           1024
510	|cooling_device0:
511	    |---type:			Processor
512	    |---max_state:		8
513	    |---cur_state:		0
515	|cooling_device3:
516	    |---type:			Fan
517	    |---max_state:		2
518	    |---cur_state:		0
520	/sys/class/hwmon:
522	|hwmon0:
523	    |---name:			acpitz
524	    |---temp1_input:		37000
525	    |---temp1_crit:		100000
527	4. Event Notification
529	The framework includes a simple notification mechanism, in the form of a
530	netlink event. Netlink socket initialization is done during the _init_
531	of the framework. Drivers which intend to use the notification mechanism
532	just need to call thermal_generate_netlink_event() with two arguments viz
533	(originator, event). The originator is a pointer to struct thermal_zone_device
534	from where the event has been originated. An integer which represents the
535	thermal zone device will be used in the message to identify the zone. The
536	event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
537	THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
538	crosses any of the configured thresholds.
540	5. Export Symbol APIs:
542	5.1: get_tz_trend:
543	This function returns the trend of a thermal zone, i.e the rate of change
544	of temperature of the thermal zone. Ideally, the thermal sensor drivers
545	are supposed to implement the callback. If they don't, the thermal
546	framework calculated the trend by comparing the previous and the current
547	temperature values.
549	5.2:get_thermal_instance:
550	This function returns the thermal_instance corresponding to a given
551	{thermal_zone, cooling_device, trip_point} combination. Returns NULL
552	if such an instance does not exist.
554	5.3:thermal_notify_framework:
555	This function handles the trip events from sensor drivers. It starts
556	throttling the cooling devices according to the policy configured.
557	For CRITICAL and HOT trip points, this notifies the respective drivers,
558	and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
559	The throttling policy is based on the configured platform data; if no
560	platform data is provided, this uses the step_wise throttling policy.
562	5.4:thermal_cdev_update:
563	This function serves as an arbitrator to set the state of a cooling
564	device. It sets the cooling device to the deepest cooling state if
565	possible.
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