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Based on kernel version 4.3. Page generated on 2015-11-02 12:51 EST.

1	Generic Thermal Sysfs driver How To
2	===================================
3	
4	Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
5	
6	Updated: 2 January 2008
7	
8	Copyright (c)  2008 Intel Corporation
9	
10	
11	0. Introduction
12	
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.
16	
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.
21	
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.
27	
28	[0-*]	denotes any positive number starting from 0
29	[1-*]	denotes any positive number starting from 1
30	
31	1. thermal sysfs driver interface functions
32	
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))
39	
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.
43	
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).
67	
68	
69	1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
70	
71	    This interface function removes the thermal zone device.
72	    It deletes the corresponding entry form /sys/class/thermal folder and
73	    unbind all the thermal cooling devices it uses.
74	
75	1.2 thermal cooling device interface
76	1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
77			void *devdata, struct thermal_cooling_device_ops *)
78	
79	    This interface function adds a new thermal cooling device (fan/processor/...)
80	    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
81	    to all the thermal zone devices register at the same time.
82	    name: the cooling device name.
83	    devdata: device private data.
84	    ops: thermal cooling devices call-backs.
85		.get_max_state: get the Maximum throttle state of the cooling device.
86		.get_cur_state: get the Current throttle state of the cooling device.
87		.set_cur_state: set the Current throttle state of the cooling device.
88	
89	1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
90	
91	    This interface function remove the thermal cooling device.
92	    It deletes the corresponding entry form /sys/class/thermal folder and
93	    unbind itself from all the thermal zone devices using it.
94	
95	1.3 interface for binding a thermal zone device with a thermal cooling device
96	1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
97		int trip, struct thermal_cooling_device *cdev,
98		unsigned long upper, unsigned long lower, unsigned int weight);
99	
100	    This interface function bind a thermal cooling device to the certain trip
101	    point of a thermal zone device.
102	    This function is usually called in the thermal zone device .bind callback.
103	    tz: the thermal zone device
104	    cdev: thermal cooling device
105	    trip: indicates which trip point the cooling devices is associated with
106		  in this thermal zone.
107	    upper:the Maximum cooling state for this trip point.
108	          THERMAL_NO_LIMIT means no upper limit,
109		  and the cooling device can be in max_state.
110	    lower:the Minimum cooling state can be used for this trip point.
111	          THERMAL_NO_LIMIT means no lower limit,
112		  and the cooling device can be in cooling state 0.
113	    weight: the influence of this cooling device in this thermal
114	            zone.  See 1.4.1 below for more information.
115	
116	1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
117			int trip, struct thermal_cooling_device *cdev);
118	
119	    This interface function unbind a thermal cooling device from the certain
120	    trip point of a thermal zone device. This function is usually called in
121	    the thermal zone device .unbind callback.
122	    tz: the thermal zone device
123	    cdev: thermal cooling device
124	    trip: indicates which trip point the cooling devices is associated with
125		  in this thermal zone.
126	
127	1.4 Thermal Zone Parameters
128	1.4.1 struct thermal_bind_params
129	    This structure defines the following parameters that are used to bind
130	    a zone with a cooling device for a particular trip point.
131	    .cdev: The cooling device pointer
132	    .weight: The 'influence' of a particular cooling device on this
133	             zone. This is relative to the rest of the cooling
134	             devices. For example, if all cooling devices have a
135	             weight of 1, then they all contribute the same. You can
136	             use percentages if you want, but it's not mandatory. A
137	             weight of 0 means that this cooling device doesn't
138	             contribute to the cooling of this zone unless all cooling
139	             devices have a weight of 0. If all weights are 0, then
140	             they all contribute the same.
141	    .trip_mask:This is a bit mask that gives the binding relation between
142	               this thermal zone and cdev, for a particular trip point.
143	               If nth bit is set, then the cdev and thermal zone are bound
144	               for trip point n.
145	    .limits: This is an array of cooling state limits. Must have exactly
146	         2 * thermal_zone.number_of_trip_points. It is an array consisting
147	         of tuples <lower-state upper-state> of state limits. Each trip
148	         will be associated with one state limit tuple when binding.
149	         A NULL pointer means <THERMAL_NO_LIMITS THERMAL_NO_LIMITS>
150	         on all trips. These limits are used when binding a cdev to a
151	         trip point.
152	    .match: This call back returns success(0) if the 'tz and cdev' need to
153		    be bound, as per platform data.
154	1.4.2 struct thermal_zone_params
155	    This structure defines the platform level parameters for a thermal zone.
156	    This data, for each thermal zone should come from the platform layer.
157	    This is an optional feature where some platforms can choose not to
158	    provide this data.
159	    .governor_name: Name of the thermal governor used for this zone
160	    .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
161	               is required. when no_hwmon == false, a hwmon sysfs interface
162	               will be created. when no_hwmon == true, nothing will be done.
163	               In case the thermal_zone_params is NULL, the hwmon interface
164	               will be created (for backward compatibility).
165	    .num_tbps: Number of thermal_bind_params entries for this zone
166	    .tbp: thermal_bind_params entries
167	
168	2. sysfs attributes structure
169	
170	RO	read only value
171	RW	read/write value
172	
173	Thermal sysfs attributes will be represented under /sys/class/thermal.
174	Hwmon sysfs I/F extension is also available under /sys/class/hwmon
175	if hwmon is compiled in or built as a module.
176	
177	Thermal zone device sys I/F, created once it's registered:
178	/sys/class/thermal/thermal_zone[0-*]:
179	    |---type:			Type of the thermal zone
180	    |---temp:			Current temperature
181	    |---mode:			Working mode of the thermal zone
182	    |---policy:			Thermal governor used for this zone
183	    |---available_policies:	Available thermal governors for this zone
184	    |---trip_point_[0-*]_temp:	Trip point temperature
185	    |---trip_point_[0-*]_type:	Trip point type
186	    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point
187	    |---emul_temp:		Emulated temperature set node
188	    |---sustainable_power:      Sustainable dissipatable power
189	    |---k_po:                   Proportional term during temperature overshoot
190	    |---k_pu:                   Proportional term during temperature undershoot
191	    |---k_i:                    PID's integral term in the power allocator gov
192	    |---k_d:                    PID's derivative term in the power allocator
193	    |---integral_cutoff:        Offset above which errors are accumulated
194	    |---slope:                  Slope constant applied as linear extrapolation
195	    |---offset:                 Offset constant applied as linear extrapolation
196	
197	Thermal cooling device sys I/F, created once it's registered:
198	/sys/class/thermal/cooling_device[0-*]:
199	    |---type:			Type of the cooling device(processor/fan/...)
200	    |---max_state:		Maximum cooling state of the cooling device
201	    |---cur_state:		Current cooling state of the cooling device
202	
203	
204	Then next two dynamic attributes are created/removed in pairs. They represent
205	the relationship between a thermal zone and its associated cooling device.
206	They are created/removed for each successful execution of
207	thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
208	
209	/sys/class/thermal/thermal_zone[0-*]:
210	    |---cdev[0-*]:		[0-*]th cooling device in current thermal zone
211	    |---cdev[0-*]_trip_point:	Trip point that cdev[0-*] is associated with
212	    |---cdev[0-*]_weight:       Influence of the cooling device in
213	                                this thermal zone
214	
215	Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
216	the generic thermal driver also creates a hwmon sysfs I/F for each _type_
217	of thermal zone device. E.g. the generic thermal driver registers one hwmon
218	class device and build the associated hwmon sysfs I/F for all the registered
219	ACPI thermal zones.
220	
221	/sys/class/hwmon/hwmon[0-*]:
222	    |---name:			The type of the thermal zone devices
223	    |---temp[1-*]_input:	The current temperature of thermal zone [1-*]
224	    |---temp[1-*]_critical:	The critical trip point of thermal zone [1-*]
225	
226	Please read Documentation/hwmon/sysfs-interface for additional information.
227	
228	***************************
229	* Thermal zone attributes *
230	***************************
231	
232	type
233		Strings which represent the thermal zone type.
234		This is given by thermal zone driver as part of registration.
235		E.g: "acpitz" indicates it's an ACPI thermal device.
236		In order to keep it consistent with hwmon sys attribute; this should
237		be a short, lowercase string, not containing spaces nor dashes.
238		RO, Required
239	
240	temp
241		Current temperature as reported by thermal zone (sensor).
242		Unit: millidegree Celsius
243		RO, Required
244	
245	mode
246		One of the predefined values in [enabled, disabled].
247		This file gives information about the algorithm that is currently
248		managing the thermal zone. It can be either default kernel based
249		algorithm or user space application.
250		enabled		= enable Kernel Thermal management.
251		disabled	= Preventing kernel thermal zone driver actions upon
252				  trip points so that user application can take full
253				  charge of the thermal management.
254		RW, Optional
255	
256	policy
257		One of the various thermal governors used for a particular zone.
258		RW, Required
259	
260	available_policies
261		Available thermal governors which can be used for a particular zone.
262		RO, Required
263	
264	trip_point_[0-*]_temp
265		The temperature above which trip point will be fired.
266		Unit: millidegree Celsius
267		RO, Optional
268	
269	trip_point_[0-*]_type
270		Strings which indicate the type of the trip point.
271		E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
272		thermal zone.
273		RO, Optional
274	
275	trip_point_[0-*]_hyst
276		The hysteresis value for a trip point, represented as an integer
277		Unit: Celsius
278		RW, Optional
279	
280	cdev[0-*]
281		Sysfs link to the thermal cooling device node where the sys I/F
282		for cooling device throttling control represents.
283		RO, Optional
284	
285	cdev[0-*]_trip_point
286		The trip point with which cdev[0-*] is associated in this thermal
287		zone; -1 means the cooling device is not associated with any trip
288		point.
289		RO, Optional
290	
291	cdev[0-*]_weight
292	        The influence of cdev[0-*] in this thermal zone. This value
293	        is relative to the rest of cooling devices in the thermal
294	        zone. For example, if a cooling device has a weight double
295	        than that of other, it's twice as effective in cooling the
296	        thermal zone.
297	        RW, Optional
298	
299	passive
300		Attribute is only present for zones in which the passive cooling
301		policy is not supported by native thermal driver. Default is zero
302		and can be set to a temperature (in millidegrees) to enable a
303		passive trip point for the zone. Activation is done by polling with
304		an interval of 1 second.
305		Unit: millidegrees Celsius
306		Valid values: 0 (disabled) or greater than 1000
307		RW, Optional
308	
309	emul_temp
310		Interface to set the emulated temperature method in thermal zone
311		(sensor). After setting this temperature, the thermal zone may pass
312		this temperature to platform emulation function if registered or
313		cache it locally. This is useful in debugging different temperature
314		threshold and its associated cooling action. This is write only node
315		and writing 0 on this node should disable emulation.
316		Unit: millidegree Celsius
317		WO, Optional
318	
319		  WARNING: Be careful while enabling this option on production systems,
320		  because userland can easily disable the thermal policy by simply
321		  flooding this sysfs node with low temperature values.
322	
323	sustainable_power
324		An estimate of the sustained power that can be dissipated by
325		the thermal zone. Used by the power allocator governor. For
326		more information see Documentation/thermal/power_allocator.txt
327		Unit: milliwatts
328		RW, Optional
329	
330	k_po
331		The proportional term of the power allocator governor's PID
332		controller during temperature overshoot. Temperature overshoot
333		is when the current temperature is above the "desired
334		temperature" trip point. For more information see
335		Documentation/thermal/power_allocator.txt
336		RW, Optional
337	
338	k_pu
339		The proportional term of the power allocator governor's PID
340		controller during temperature undershoot. Temperature undershoot
341		is when the current temperature is below the "desired
342		temperature" trip point. For more information see
343		Documentation/thermal/power_allocator.txt
344		RW, Optional
345	
346	k_i
347		The integral term of the power allocator governor's PID
348		controller. This term allows the PID controller to compensate
349		for long term drift. For more information see
350		Documentation/thermal/power_allocator.txt
351		RW, Optional
352	
353	k_d
354		The derivative term of the power allocator governor's PID
355		controller. For more information see
356		Documentation/thermal/power_allocator.txt
357		RW, Optional
358	
359	integral_cutoff
360		Temperature offset from the desired temperature trip point
361		above which the integral term of the power allocator
362		governor's PID controller starts accumulating errors. For
363		example, if integral_cutoff is 0, then the integral term only
364		accumulates error when temperature is above the desired
365		temperature trip point. For more information see
366		Documentation/thermal/power_allocator.txt
367		RW, Optional
368	
369	slope
370		The slope constant used in a linear extrapolation model
371		to determine a hotspot temperature based off the sensor's
372		raw readings. It is up to the device driver to determine
373		the usage of these values.
374		RW, Optional
375	
376	offset
377		The offset constant used in a linear extrapolation model
378		to determine a hotspot temperature based off the sensor's
379		raw readings. It is up to the device driver to determine
380		the usage of these values.
381		RW, Optional
382	
383	*****************************
384	* Cooling device attributes *
385	*****************************
386	
387	type
388		String which represents the type of device, e.g:
389		- for generic ACPI: should be "Fan", "Processor" or "LCD"
390		- for memory controller device on intel_menlow platform:
391		  should be "Memory controller".
392		RO, Required
393	
394	max_state
395		The maximum permissible cooling state of this cooling device.
396		RO, Required
397	
398	cur_state
399		The current cooling state of this cooling device.
400		The value can any integer numbers between 0 and max_state:
401		- cur_state == 0 means no cooling
402		- cur_state == max_state means the maximum cooling.
403		RW, Required
404	
405	3. A simple implementation
406	
407	ACPI thermal zone may support multiple trip points like critical, hot,
408	passive, active. If an ACPI thermal zone supports critical, passive,
409	active[0] and active[1] at the same time, it may register itself as a
410	thermal_zone_device (thermal_zone1) with 4 trip points in all.
411	It has one processor and one fan, which are both registered as
412	thermal_cooling_device. Both are considered to have the same
413	effectiveness in cooling the thermal zone.
414	
415	If the processor is listed in _PSL method, and the fan is listed in _AL0
416	method, the sys I/F structure will be built like this:
417	
418	/sys/class/thermal:
419	
420	|thermal_zone1:
421	    |---type:			acpitz
422	    |---temp:			37000
423	    |---mode:			enabled
424	    |---policy:			step_wise
425	    |---available_policies:	step_wise fair_share
426	    |---trip_point_0_temp:	100000
427	    |---trip_point_0_type:	critical
428	    |---trip_point_1_temp:	80000
429	    |---trip_point_1_type:	passive
430	    |---trip_point_2_temp:	70000
431	    |---trip_point_2_type:	active0
432	    |---trip_point_3_temp:	60000
433	    |---trip_point_3_type:	active1
434	    |---cdev0:			--->/sys/class/thermal/cooling_device0
435	    |---cdev0_trip_point:	1	/* cdev0 can be used for passive */
436	    |---cdev0_weight:           1024
437	    |---cdev1:			--->/sys/class/thermal/cooling_device3
438	    |---cdev1_trip_point:	2	/* cdev1 can be used for active[0]*/
439	    |---cdev1_weight:           1024
440	
441	|cooling_device0:
442	    |---type:			Processor
443	    |---max_state:		8
444	    |---cur_state:		0
445	
446	|cooling_device3:
447	    |---type:			Fan
448	    |---max_state:		2
449	    |---cur_state:		0
450	
451	/sys/class/hwmon:
452	
453	|hwmon0:
454	    |---name:			acpitz
455	    |---temp1_input:		37000
456	    |---temp1_crit:		100000
457	
458	4. Event Notification
459	
460	The framework includes a simple notification mechanism, in the form of a
461	netlink event. Netlink socket initialization is done during the _init_
462	of the framework. Drivers which intend to use the notification mechanism
463	just need to call thermal_generate_netlink_event() with two arguments viz
464	(originator, event). The originator is a pointer to struct thermal_zone_device
465	from where the event has been originated. An integer which represents the
466	thermal zone device will be used in the message to identify the zone. The
467	event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
468	THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
469	crosses any of the configured thresholds.
470	
471	5. Export Symbol APIs:
472	
473	5.1: get_tz_trend:
474	This function returns the trend of a thermal zone, i.e the rate of change
475	of temperature of the thermal zone. Ideally, the thermal sensor drivers
476	are supposed to implement the callback. If they don't, the thermal
477	framework calculated the trend by comparing the previous and the current
478	temperature values.
479	
480	5.2:get_thermal_instance:
481	This function returns the thermal_instance corresponding to a given
482	{thermal_zone, cooling_device, trip_point} combination. Returns NULL
483	if such an instance does not exist.
484	
485	5.3:thermal_notify_framework:
486	This function handles the trip events from sensor drivers. It starts
487	throttling the cooling devices according to the policy configured.
488	For CRITICAL and HOT trip points, this notifies the respective drivers,
489	and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
490	The throttling policy is based on the configured platform data; if no
491	platform data is provided, this uses the step_wise throttling policy.
492	
493	5.4:thermal_cdev_update:
494	This function serves as an arbitrator to set the state of a cooling
495	device. It sets the cooling device to the deepest cooling state if
496	possible.
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