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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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		.set_trips: set the trip points window. Whenever the current temperature
53			    is updated, the trip points immediately below and above the
54			    current temperature are found.
55		.get_mode: get the current mode (enabled/disabled) of the thermal zone.
56		    - "enabled" means the kernel thermal management is enabled.
57		    - "disabled" will prevent kernel thermal driver action upon trip points
58		      so that user applications can take charge of thermal management.
59		.set_mode: set the mode (enabled/disabled) of the thermal zone.
60		.get_trip_type: get the type of certain trip point.
61		.get_trip_temp: get the temperature above which the certain trip point
62				will be fired.
63		.set_emul_temp: set the emulation temperature which helps in debugging
64				different threshold temperature points.
65	    tzp: thermal zone platform parameters.
66	    passive_delay: number of milliseconds to wait between polls when
67		performing passive cooling.
68	    polling_delay: number of milliseconds to wait between polls when checking
69		whether trip points have been crossed (0 for interrupt driven systems).
72	1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
74	    This interface function removes the thermal zone device.
75	    It deletes the corresponding entry from /sys/class/thermal folder and
76	    unbinds all the thermal cooling devices it uses.
78	1.1.3 struct thermal_zone_device *thermal_zone_of_sensor_register(
79			struct device *dev, int sensor_id, void *data,
80			const struct thermal_zone_of_device_ops *ops)
82		This interface adds a new sensor to a DT thermal zone.
83		This function will search the list of thermal zones described in
84		device tree and look for the zone that refer to the sensor device
85		pointed by dev->of_node as temperature providers. For the zone
86		pointing to the sensor node, the sensor will be added to the DT
87		thermal zone device.
89		The parameters for this interface are:
90		dev:		Device node of sensor containing valid node pointer in
91				dev->of_node.
92		sensor_id:	a sensor identifier, in case the sensor IP has more
93				than one sensors
94		data:		a private pointer (owned by the caller) that will be
95				passed back, when a temperature reading is needed.
96		ops:		struct thermal_zone_of_device_ops *.
98				get_temp:	a pointer to a function that reads the
99						sensor temperature. This is mandatory
100						callback provided by sensor driver.
101				set_trips:      a pointer to a function that sets a
102						temperature window. When this window is
103						left the driver must inform the thermal
104						core via thermal_zone_device_update.
105				get_trend: 	a pointer to a function that reads the
106						sensor temperature trend.
107				set_emul_temp:	a pointer to a function that sets
108						sensor emulated temperature.
109		The thermal zone temperature is provided by the get_temp() function
110		pointer of thermal_zone_of_device_ops. When called, it will
111		have the private pointer @data back.
113		It returns error pointer if fails otherwise valid thermal zone device
114		handle. Caller should check the return handle with IS_ERR() for finding
115		whether success or not.
117	1.1.4 void thermal_zone_of_sensor_unregister(struct device *dev,
118			struct thermal_zone_device *tzd)
120		This interface unregisters a sensor from a DT thermal zone which was
121		successfully added by interface thermal_zone_of_sensor_register().
122		This function removes the sensor callbacks and private data from the
123		thermal zone device registered with thermal_zone_of_sensor_register()
124		interface. It will also silent the zone by remove the .get_temp() and
125		get_trend() thermal zone device callbacks.
127	1.1.5 struct thermal_zone_device *devm_thermal_zone_of_sensor_register(
128			struct device *dev, int sensor_id,
129			void *data, const struct thermal_zone_of_device_ops *ops)
131		This interface is resource managed version of
132		thermal_zone_of_sensor_register().
133		All details of thermal_zone_of_sensor_register() described in
134		section 1.1.3 is applicable here.
135		The benefit of using this interface to register sensor is that it
136		is not require to explicitly call thermal_zone_of_sensor_unregister()
137		in error path or during driver unbinding as this is done by driver
138		resource manager.
140	1.1.6 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
141			struct thermal_zone_device *tzd)
143		This interface is resource managed version of
144		thermal_zone_of_sensor_unregister().
145		All details of thermal_zone_of_sensor_unregister() described in
146		section 1.1.4 is applicable here.
147		Normally this function will not need to be called and the resource
148		management code will ensure that the resource is freed.
150	1.1.7 int thermal_zone_get_slope(struct thermal_zone_device *tz)
152		This interface is used to read the slope attribute value
153		for the thermal zone device, which might be useful for platform
154		drivers for temperature calculations.
156	1.1.8 int thermal_zone_get_offset(struct thermal_zone_device *tz)
158		This interface is used to read the offset attribute value
159		for the thermal zone device, which might be useful for platform
160		drivers for temperature calculations.
162	1.2 thermal cooling device interface
163	1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
164			void *devdata, struct thermal_cooling_device_ops *)
166	    This interface function adds a new thermal cooling device (fan/processor/...)
167	    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
168	    to all the thermal zone devices registered at the same time.
169	    name: the cooling device name.
170	    devdata: device private data.
171	    ops: thermal cooling devices call-backs.
172		.get_max_state: get the Maximum throttle state of the cooling device.
173		.get_cur_state: get the Currently requested throttle state of the cooling device.
174		.set_cur_state: set the Current throttle state of the cooling device.
176	1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
178	    This interface function removes the thermal cooling device.
179	    It deletes the corresponding entry from /sys/class/thermal folder and
180	    unbinds itself from all the thermal zone devices using it.
182	1.3 interface for binding a thermal zone device with a thermal cooling device
183	1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
184		int trip, struct thermal_cooling_device *cdev,
185		unsigned long upper, unsigned long lower, unsigned int weight);
187	    This interface function binds a thermal cooling device to a particular trip
188	    point of a thermal zone device.
189	    This function is usually called in the thermal zone device .bind 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.
194	    upper:the Maximum cooling state for this trip point.
195	          THERMAL_NO_LIMIT means no upper limit,
196		  and the cooling device can be in max_state.
197	    lower:the Minimum cooling state can be used for this trip point.
198	          THERMAL_NO_LIMIT means no lower limit,
199		  and the cooling device can be in cooling state 0.
200	    weight: the influence of this cooling device in this thermal
201	            zone.  See 1.4.1 below for more information.
203	1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
204			int trip, struct thermal_cooling_device *cdev);
206	    This interface function unbinds a thermal cooling device from a particular
207	    trip point of a thermal zone device. This function is usually called in
208	    the thermal zone device .unbind callback.
209	    tz: the thermal zone device
210	    cdev: thermal cooling device
211	    trip: indicates which trip point in this thermal zone the cooling device
212	          is associated with.
214	1.4 Thermal Zone Parameters
215	1.4.1 struct thermal_bind_params
216	    This structure defines the following parameters that are used to bind
217	    a zone with a cooling device for a particular trip point.
218	    .cdev: The cooling device pointer
219	    .weight: The 'influence' of a particular cooling device on this
220	             zone. This is relative to the rest of the cooling
221	             devices. For example, if all cooling devices have a
222	             weight of 1, then they all contribute the same. You can
223	             use percentages if you want, but it's not mandatory. A
224	             weight of 0 means that this cooling device doesn't
225	             contribute to the cooling of this zone unless all cooling
226	             devices have a weight of 0. If all weights are 0, then
227	             they all contribute the same.
228	    .trip_mask:This is a bit mask that gives the binding relation between
229	               this thermal zone and cdev, for a particular trip point.
230	               If nth bit is set, then the cdev and thermal zone are bound
231	               for trip point n.
232	    .binding_limits: This is an array of cooling state limits. Must have
233	                     exactly 2 * thermal_zone.number_of_trip_points. It is an
234	                     array consisting of tuples <lower-state upper-state> of
235	                     state limits. Each trip will be associated with one state
236	                     limit tuple when binding. A NULL pointer means
237	                     <THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips.
238	                     These limits are used when binding a cdev to a trip point.
239	    .match: This call back returns success(0) if the 'tz and cdev' need to
240		    be bound, as per platform data.
241	1.4.2 struct thermal_zone_params
242	    This structure defines the platform level parameters for a thermal zone.
243	    This data, for each thermal zone should come from the platform layer.
244	    This is an optional feature where some platforms can choose not to
245	    provide this data.
246	    .governor_name: Name of the thermal governor used for this zone
247	    .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
248	               is required. when no_hwmon == false, a hwmon sysfs interface
249	               will be created. when no_hwmon == true, nothing will be done.
250	               In case the thermal_zone_params is NULL, the hwmon interface
251	               will be created (for backward compatibility).
252	    .num_tbps: Number of thermal_bind_params entries for this zone
253	    .tbp: thermal_bind_params entries
255	2. sysfs attributes structure
257	RO	read only value
258	RW	read/write value
260	Thermal sysfs attributes will be represented under /sys/class/thermal.
261	Hwmon sysfs I/F extension is also available under /sys/class/hwmon
262	if hwmon is compiled in or built as a module.
264	Thermal zone device sys I/F, created once it's registered:
265	/sys/class/thermal/thermal_zone[0-*]:
266	    |---type:			Type of the thermal zone
267	    |---temp:			Current temperature
268	    |---mode:			Working mode of the thermal zone
269	    |---policy:			Thermal governor used for this zone
270	    |---available_policies:	Available thermal governors for this zone
271	    |---trip_point_[0-*]_temp:	Trip point temperature
272	    |---trip_point_[0-*]_type:	Trip point type
273	    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point
274	    |---emul_temp:		Emulated temperature set node
275	    |---sustainable_power:      Sustainable dissipatable power
276	    |---k_po:                   Proportional term during temperature overshoot
277	    |---k_pu:                   Proportional term during temperature undershoot
278	    |---k_i:                    PID's integral term in the power allocator gov
279	    |---k_d:                    PID's derivative term in the power allocator
280	    |---integral_cutoff:        Offset above which errors are accumulated
281	    |---slope:                  Slope constant applied as linear extrapolation
282	    |---offset:                 Offset constant applied as linear extrapolation
284	Thermal cooling device sys I/F, created once it's registered:
285	/sys/class/thermal/cooling_device[0-*]:
286	    |---type:			Type of the cooling device(processor/fan/...)
287	    |---max_state:		Maximum cooling state of the cooling device
288	    |---cur_state:		Current cooling state of the cooling device
291	Then next two dynamic attributes are created/removed in pairs. They represent
292	the relationship between a thermal zone and its associated cooling device.
293	They are created/removed for each successful execution of
294	thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
296	/sys/class/thermal/thermal_zone[0-*]:
297	    |---cdev[0-*]:		[0-*]th cooling device in current thermal zone
298	    |---cdev[0-*]_trip_point:	Trip point that cdev[0-*] is associated with
299	    |---cdev[0-*]_weight:       Influence of the cooling device in
300	                                this thermal zone
302	Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
303	the generic thermal driver also creates a hwmon sysfs I/F for each _type_
304	of thermal zone device. E.g. the generic thermal driver registers one hwmon
305	class device and build the associated hwmon sysfs I/F for all the registered
306	ACPI thermal zones.
308	/sys/class/hwmon/hwmon[0-*]:
309	    |---name:			The type of the thermal zone devices
310	    |---temp[1-*]_input:	The current temperature of thermal zone [1-*]
311	    |---temp[1-*]_critical:	The critical trip point of thermal zone [1-*]
313	Please read Documentation/hwmon/sysfs-interface for additional information.
315	***************************
316	* Thermal zone attributes *
317	***************************
319	type
320		Strings which represent the thermal zone type.
321		This is given by thermal zone driver as part of registration.
322		E.g: "acpitz" indicates it's an ACPI thermal device.
323		In order to keep it consistent with hwmon sys attribute; this should
324		be a short, lowercase string, not containing spaces nor dashes.
325		RO, Required
327	temp
328		Current temperature as reported by thermal zone (sensor).
329		Unit: millidegree Celsius
330		RO, Required
332	mode
333		One of the predefined values in [enabled, disabled].
334		This file gives information about the algorithm that is currently
335		managing the thermal zone. It can be either default kernel based
336		algorithm or user space application.
337		enabled		= enable Kernel Thermal management.
338		disabled	= Preventing kernel thermal zone driver actions upon
339				  trip points so that user application can take full
340				  charge of the thermal management.
341		RW, Optional
343	policy
344		One of the various thermal governors used for a particular zone.
345		RW, Required
347	available_policies
348		Available thermal governors which can be used for a particular zone.
349		RO, Required
351	trip_point_[0-*]_temp
352		The temperature above which trip point will be fired.
353		Unit: millidegree Celsius
354		RO, Optional
356	trip_point_[0-*]_type
357		Strings which indicate the type of the trip point.
358		E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
359		thermal zone.
360		RO, Optional
362	trip_point_[0-*]_hyst
363		The hysteresis value for a trip point, represented as an integer
364		Unit: Celsius
365		RW, Optional
367	cdev[0-*]
368		Sysfs link to the thermal cooling device node where the sys I/F
369		for cooling device throttling control represents.
370		RO, Optional
372	cdev[0-*]_trip_point
373		The trip point in this thermal zone which cdev[0-*] is associated
374		with; -1 means the cooling device is not associated with any trip
375		point.
376		RO, Optional
378	cdev[0-*]_weight
379	        The influence of cdev[0-*] in this thermal zone. This value
380	        is relative to the rest of cooling devices in the thermal
381	        zone. For example, if a cooling device has a weight double
382	        than that of other, it's twice as effective in cooling the
383	        thermal zone.
384	        RW, Optional
386	passive
387		Attribute is only present for zones in which the passive cooling
388		policy is not supported by native thermal driver. Default is zero
389		and can be set to a temperature (in millidegrees) to enable a
390		passive trip point for the zone. Activation is done by polling with
391		an interval of 1 second.
392		Unit: millidegrees Celsius
393		Valid values: 0 (disabled) or greater than 1000
394		RW, Optional
396	emul_temp
397		Interface to set the emulated temperature method in thermal zone
398		(sensor). After setting this temperature, the thermal zone may pass
399		this temperature to platform emulation function if registered or
400		cache it locally. This is useful in debugging different temperature
401		threshold and its associated cooling action. This is write only node
402		and writing 0 on this node should disable emulation.
403		Unit: millidegree Celsius
404		WO, Optional
406		  WARNING: Be careful while enabling this option on production systems,
407		  because userland can easily disable the thermal policy by simply
408		  flooding this sysfs node with low temperature values.
410	sustainable_power
411		An estimate of the sustained power that can be dissipated by
412		the thermal zone. Used by the power allocator governor. For
413		more information see Documentation/thermal/power_allocator.txt
414		Unit: milliwatts
415		RW, Optional
417	k_po
418		The proportional term of the power allocator governor's PID
419		controller during temperature overshoot. Temperature overshoot
420		is when the current temperature is above the "desired
421		temperature" trip point. For more information see
422		Documentation/thermal/power_allocator.txt
423		RW, Optional
425	k_pu
426		The proportional term of the power allocator governor's PID
427		controller during temperature undershoot. Temperature undershoot
428		is when the current temperature is below the "desired
429		temperature" trip point. For more information see
430		Documentation/thermal/power_allocator.txt
431		RW, Optional
433	k_i
434		The integral term of the power allocator governor's PID
435		controller. This term allows the PID controller to compensate
436		for long term drift. For more information see
437		Documentation/thermal/power_allocator.txt
438		RW, Optional
440	k_d
441		The derivative term of the power allocator governor's PID
442		controller. For more information see
443		Documentation/thermal/power_allocator.txt
444		RW, Optional
446	integral_cutoff
447		Temperature offset from the desired temperature trip point
448		above which the integral term of the power allocator
449		governor's PID controller starts accumulating errors. For
450		example, if integral_cutoff is 0, then the integral term only
451		accumulates error when temperature is above the desired
452		temperature trip point. For more information see
453		Documentation/thermal/power_allocator.txt
454		Unit: millidegree Celsius
455		RW, Optional
457	slope
458		The slope constant used in a linear extrapolation model
459		to determine a hotspot temperature based off the sensor's
460		raw readings. It is up to the device driver to determine
461		the usage of these values.
462		RW, Optional
464	offset
465		The offset constant used in a linear extrapolation model
466		to determine a hotspot temperature based off the sensor's
467		raw readings. It is up to the device driver to determine
468		the usage of these values.
469		RW, Optional
471	*****************************
472	* Cooling device attributes *
473	*****************************
475	type
476		String which represents the type of device, e.g:
477		- for generic ACPI: should be "Fan", "Processor" or "LCD"
478		- for memory controller device on intel_menlow platform:
479		  should be "Memory controller".
480		RO, Required
482	max_state
483		The maximum permissible cooling state of this cooling device.
484		RO, Required
486	cur_state
487		The current cooling state of this cooling device.
488		The value can any integer numbers between 0 and max_state:
489		- cur_state == 0 means no cooling
490		- cur_state == max_state means the maximum cooling.
491		RW, Required
493	3. A simple implementation
495	ACPI thermal zone may support multiple trip points like critical, hot,
496	passive, active. If an ACPI thermal zone supports critical, passive,
497	active[0] and active[1] at the same time, it may register itself as a
498	thermal_zone_device (thermal_zone1) with 4 trip points in all.
499	It has one processor and one fan, which are both registered as
500	thermal_cooling_device. Both are considered to have the same
501	effectiveness in cooling the thermal zone.
503	If the processor is listed in _PSL method, and the fan is listed in _AL0
504	method, the sys I/F structure will be built like this:
506	/sys/class/thermal:
508	|thermal_zone1:
509	    |---type:			acpitz
510	    |---temp:			37000
511	    |---mode:			enabled
512	    |---policy:			step_wise
513	    |---available_policies:	step_wise fair_share
514	    |---trip_point_0_temp:	100000
515	    |---trip_point_0_type:	critical
516	    |---trip_point_1_temp:	80000
517	    |---trip_point_1_type:	passive
518	    |---trip_point_2_temp:	70000
519	    |---trip_point_2_type:	active0
520	    |---trip_point_3_temp:	60000
521	    |---trip_point_3_type:	active1
522	    |---cdev0:			--->/sys/class/thermal/cooling_device0
523	    |---cdev0_trip_point:	1	/* cdev0 can be used for passive */
524	    |---cdev0_weight:           1024
525	    |---cdev1:			--->/sys/class/thermal/cooling_device3
526	    |---cdev1_trip_point:	2	/* cdev1 can be used for active[0]*/
527	    |---cdev1_weight:           1024
529	|cooling_device0:
530	    |---type:			Processor
531	    |---max_state:		8
532	    |---cur_state:		0
534	|cooling_device3:
535	    |---type:			Fan
536	    |---max_state:		2
537	    |---cur_state:		0
539	/sys/class/hwmon:
541	|hwmon0:
542	    |---name:			acpitz
543	    |---temp1_input:		37000
544	    |---temp1_crit:		100000
546	4. Event Notification
548	The framework includes a simple notification mechanism, in the form of a
549	netlink event. Netlink socket initialization is done during the _init_
550	of the framework. Drivers which intend to use the notification mechanism
551	just need to call thermal_generate_netlink_event() with two arguments viz
552	(originator, event). The originator is a pointer to struct thermal_zone_device
553	from where the event has been originated. An integer which represents the
554	thermal zone device will be used in the message to identify the zone. The
555	event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
556	THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
557	crosses any of the configured thresholds.
559	5. Export Symbol APIs:
561	5.1: get_tz_trend:
562	This function returns the trend of a thermal zone, i.e the rate of change
563	of temperature of the thermal zone. Ideally, the thermal sensor drivers
564	are supposed to implement the callback. If they don't, the thermal
565	framework calculated the trend by comparing the previous and the current
566	temperature values.
568	5.2:get_thermal_instance:
569	This function returns the thermal_instance corresponding to a given
570	{thermal_zone, cooling_device, trip_point} combination. Returns NULL
571	if such an instance does not exist.
573	5.3:thermal_notify_framework:
574	This function handles the trip events from sensor drivers. It starts
575	throttling the cooling devices according to the policy configured.
576	For CRITICAL and HOT trip points, this notifies the respective drivers,
577	and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
578	The throttling policy is based on the configured platform data; if no
579	platform data is provided, this uses the step_wise throttling policy.
581	5.4:thermal_cdev_update:
582	This function serves as an arbitrator to set the state of a cooling
583	device. It sets the cooling device to the deepest cooling state if
584	possible.
586	6. thermal_emergency_poweroff:
588	On an event of critical trip temperature crossing. Thermal framework
589	allows the system to shutdown gracefully by calling orderly_poweroff().
590	In the event of a failure of orderly_poweroff() to shut down the system
591	we are in danger of keeping the system alive at undesirably high
592	temperatures. To mitigate this high risk scenario we program a work
593	queue to fire after a pre-determined number of seconds to start
594	an emergency shutdown of the device using the kernel_power_off()
595	function. In case kernel_power_off() fails then finally
596	emergency_restart() is called in the worst case.
598	The delay should be carefully profiled so as to give adequate time for
599	orderly_poweroff(). In case of failure of an orderly_poweroff() the
600	emergency poweroff kicks in after the delay has elapsed and shuts down
601	the system.
603	If set to 0 emergency poweroff will not be supported. So a carefully
604	profiled non-zero positive value is a must for emergerncy poweroff to be
605	triggered.
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