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Based on kernel version 4.1. Page generated on 2015-06-28 12:14 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 form /sys/class/thermal folder and
73	    unbind all the thermal cooling devices it uses.
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 *)
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.
89	1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
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.
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);
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.
114	1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
115			int trip, struct thermal_cooling_device *cdev);
117	    This interface function unbind a thermal cooling device from the certain
118	    trip point of a thermal zone device. This function is usually called in
119	    the thermal zone device .unbind callback.
120	    tz: the thermal zone device
121	    cdev: thermal cooling device
122	    trip: indicates which trip point the cooling devices is associated with
123		  in this thermal zone.
125	1.4 Thermal Zone Parameters
126	1.4.1 struct thermal_bind_params
127	    This structure defines the following parameters that are used to bind
128	    a zone with a cooling device for a particular trip point.
129	    .cdev: The cooling device pointer
130	    .weight: The 'influence' of a particular cooling device on this zone.
131	             This is on a percentage scale. The sum of all these weights
132	             (for a particular zone) cannot exceed 100.
133	    .trip_mask:This is a bit mask that gives the binding relation between
134	               this thermal zone and cdev, for a particular trip point.
135	               If nth bit is set, then the cdev and thermal zone are bound
136	               for trip point n.
137	    .limits: This is an array of cooling state limits. Must have exactly
138	         2 * thermal_zone.number_of_trip_points. It is an array consisting
139	         of tuples <lower-state upper-state> of state limits. Each trip
140	         will be associated with one state limit tuple when binding.
141	         A NULL pointer means <THERMAL_NO_LIMITS THERMAL_NO_LIMITS>
142	         on all trips. These limits are used when binding a cdev to a
143	         trip point.
144	    .match: This call back returns success(0) if the 'tz and cdev' need to
145		    be bound, as per platform data.
146	1.4.2 struct thermal_zone_params
147	    This structure defines the platform level parameters for a thermal zone.
148	    This data, for each thermal zone should come from the platform layer.
149	    This is an optional feature where some platforms can choose not to
150	    provide this data.
151	    .governor_name: Name of the thermal governor used for this zone
152	    .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
153	               is required. when no_hwmon == false, a hwmon sysfs interface
154	               will be created. when no_hwmon == true, nothing will be done.
155	               In case the thermal_zone_params is NULL, the hwmon interface
156	               will be created (for backward compatibility).
157	    .num_tbps: Number of thermal_bind_params entries for this zone
158	    .tbp: thermal_bind_params entries
160	2. sysfs attributes structure
162	RO	read only value
163	RW	read/write value
165	Thermal sysfs attributes will be represented under /sys/class/thermal.
166	Hwmon sysfs I/F extension is also available under /sys/class/hwmon
167	if hwmon is compiled in or built as a module.
169	Thermal zone device sys I/F, created once it's registered:
170	/sys/class/thermal/thermal_zone[0-*]:
171	    |---type:			Type of the thermal zone
172	    |---temp:			Current temperature
173	    |---mode:			Working mode of the thermal zone
174	    |---policy:			Thermal governor used for this zone
175	    |---trip_point_[0-*]_temp:	Trip point temperature
176	    |---trip_point_[0-*]_type:	Trip point type
177	    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point
178	    |---emul_temp:		Emulated temperature set node
180	Thermal cooling device sys I/F, created once it's registered:
181	/sys/class/thermal/cooling_device[0-*]:
182	    |---type:			Type of the cooling device(processor/fan/...)
183	    |---max_state:		Maximum cooling state of the cooling device
184	    |---cur_state:		Current cooling state of the cooling device
187	Then next two dynamic attributes are created/removed in pairs. They represent
188	the relationship between a thermal zone and its associated cooling device.
189	They are created/removed for each successful execution of
190	thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
192	/sys/class/thermal/thermal_zone[0-*]:
193	    |---cdev[0-*]:		[0-*]th cooling device in current thermal zone
194	    |---cdev[0-*]_trip_point:	Trip point that cdev[0-*] is associated with
196	Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
197	the generic thermal driver also creates a hwmon sysfs I/F for each _type_
198	of thermal zone device. E.g. the generic thermal driver registers one hwmon
199	class device and build the associated hwmon sysfs I/F for all the registered
200	ACPI thermal zones.
202	/sys/class/hwmon/hwmon[0-*]:
203	    |---name:			The type of the thermal zone devices
204	    |---temp[1-*]_input:	The current temperature of thermal zone [1-*]
205	    |---temp[1-*]_critical:	The critical trip point of thermal zone [1-*]
207	Please read Documentation/hwmon/sysfs-interface for additional information.
209	***************************
210	* Thermal zone attributes *
211	***************************
213	type
214		Strings which represent the thermal zone type.
215		This is given by thermal zone driver as part of registration.
216		E.g: "acpitz" indicates it's an ACPI thermal device.
217		In order to keep it consistent with hwmon sys attribute; this should
218		be a short, lowercase string, not containing spaces nor dashes.
219		RO, Required
221	temp
222		Current temperature as reported by thermal zone (sensor).
223		Unit: millidegree Celsius
224		RO, Required
226	mode
227		One of the predefined values in [enabled, disabled].
228		This file gives information about the algorithm that is currently
229		managing the thermal zone. It can be either default kernel based
230		algorithm or user space application.
231		enabled		= enable Kernel Thermal management.
232		disabled	= Preventing kernel thermal zone driver actions upon
233				  trip points so that user application can take full
234				  charge of the thermal management.
235		RW, Optional
237	policy
238		One of the various thermal governors used for a particular zone.
239		RW, Required
241	trip_point_[0-*]_temp
242		The temperature above which trip point will be fired.
243		Unit: millidegree Celsius
244		RO, Optional
246	trip_point_[0-*]_type
247		Strings which indicate the type of the trip point.
248		E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
249		thermal zone.
250		RO, Optional
252	trip_point_[0-*]_hyst
253		The hysteresis value for a trip point, represented as an integer
254		Unit: Celsius
255		RW, Optional
257	cdev[0-*]
258		Sysfs link to the thermal cooling device node where the sys I/F
259		for cooling device throttling control represents.
260		RO, Optional
262	cdev[0-*]_trip_point
263		The trip point with which cdev[0-*] is associated in this thermal
264		zone; -1 means the cooling device is not associated with any trip
265		point.
266		RO, Optional
268	passive
269		Attribute is only present for zones in which the passive cooling
270		policy is not supported by native thermal driver. Default is zero
271		and can be set to a temperature (in millidegrees) to enable a
272		passive trip point for the zone. Activation is done by polling with
273		an interval of 1 second.
274		Unit: millidegrees Celsius
275		Valid values: 0 (disabled) or greater than 1000
276		RW, Optional
278	emul_temp
279		Interface to set the emulated temperature method in thermal zone
280		(sensor). After setting this temperature, the thermal zone may pass
281		this temperature to platform emulation function if registered or
282		cache it locally. This is useful in debugging different temperature
283		threshold and its associated cooling action. This is write only node
284		and writing 0 on this node should disable emulation.
285		Unit: millidegree Celsius
286		WO, Optional
288		  WARNING: Be careful while enabling this option on production systems,
289		  because userland can easily disable the thermal policy by simply
290		  flooding this sysfs node with low temperature values.
292	*****************************
293	* Cooling device attributes *
294	*****************************
296	type
297		String which represents the type of device, e.g:
298		- for generic ACPI: should be "Fan", "Processor" or "LCD"
299		- for memory controller device on intel_menlow platform:
300		  should be "Memory controller".
301		RO, Required
303	max_state
304		The maximum permissible cooling state of this cooling device.
305		RO, Required
307	cur_state
308		The current cooling state of this cooling device.
309		The value can any integer numbers between 0 and max_state:
310		- cur_state == 0 means no cooling
311		- cur_state == max_state means the maximum cooling.
312		RW, Required
314	3. A simple implementation
316	ACPI thermal zone may support multiple trip points like critical, hot,
317	passive, active. If an ACPI thermal zone supports critical, passive,
318	active[0] and active[1] at the same time, it may register itself as a
319	thermal_zone_device (thermal_zone1) with 4 trip points in all.
320	It has one processor and one fan, which are both registered as
321	thermal_cooling_device.
323	If the processor is listed in _PSL method, and the fan is listed in _AL0
324	method, the sys I/F structure will be built like this:
326	/sys/class/thermal:
328	|thermal_zone1:
329	    |---type:			acpitz
330	    |---temp:			37000
331	    |---mode:			enabled
332	    |---policy:			step_wise
333	    |---trip_point_0_temp:	100000
334	    |---trip_point_0_type:	critical
335	    |---trip_point_1_temp:	80000
336	    |---trip_point_1_type:	passive
337	    |---trip_point_2_temp:	70000
338	    |---trip_point_2_type:	active0
339	    |---trip_point_3_temp:	60000
340	    |---trip_point_3_type:	active1
341	    |---cdev0:			--->/sys/class/thermal/cooling_device0
342	    |---cdev0_trip_point:	1	/* cdev0 can be used for passive */
343	    |---cdev1:			--->/sys/class/thermal/cooling_device3
344	    |---cdev1_trip_point:	2	/* cdev1 can be used for active[0]*/
346	|cooling_device0:
347	    |---type:			Processor
348	    |---max_state:		8
349	    |---cur_state:		0
351	|cooling_device3:
352	    |---type:			Fan
353	    |---max_state:		2
354	    |---cur_state:		0
356	/sys/class/hwmon:
358	|hwmon0:
359	    |---name:			acpitz
360	    |---temp1_input:		37000
361	    |---temp1_crit:		100000
363	4. Event Notification
365	The framework includes a simple notification mechanism, in the form of a
366	netlink event. Netlink socket initialization is done during the _init_
367	of the framework. Drivers which intend to use the notification mechanism
368	just need to call thermal_generate_netlink_event() with two arguments viz
369	(originator, event). The originator is a pointer to struct thermal_zone_device
370	from where the event has been originated. An integer which represents the
371	thermal zone device will be used in the message to identify the zone. The
372	event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
373	THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
374	crosses any of the configured thresholds.
376	5. Export Symbol APIs:
378	5.1: get_tz_trend:
379	This function returns the trend of a thermal zone, i.e the rate of change
380	of temperature of the thermal zone. Ideally, the thermal sensor drivers
381	are supposed to implement the callback. If they don't, the thermal
382	framework calculated the trend by comparing the previous and the current
383	temperature values.
385	5.2:get_thermal_instance:
386	This function returns the thermal_instance corresponding to a given
387	{thermal_zone, cooling_device, trip_point} combination. Returns NULL
388	if such an instance does not exist.
390	5.3:thermal_notify_framework:
391	This function handles the trip events from sensor drivers. It starts
392	throttling the cooling devices according to the policy configured.
393	For CRITICAL and HOT trip points, this notifies the respective drivers,
394	and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
395	The throttling policy is based on the configured platform data; if no
396	platform data is provided, this uses the step_wise throttling policy.
398	5.4:thermal_cdev_update:
399	This function serves as an arbitrator to set the state of a cooling
400	device. It sets the cooling device to the deepest cooling state if
401	possible.
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