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1Generic Thermal Sysfs driver How To
2=========================
3
4Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
5
6Updated: 2 January 2008
7
8Copyright (c) 2008 Intel Corporation
9
10
110. Introduction
12
13The generic thermal sysfs provides a set of interfaces for thermal zone devices (sensors)
14and thermal cooling devices (fan, processor...) to register with the thermal management
15solution and to be a part of it.
16
17This how-to focusses on enabling new thermal zone and cooling devices to participate
18in thermal management.
19This solution is platform independent and any type of thermal zone devices and
20cooling devices should be able to make use of the infrastructure.
21
22The main task of the thermal sysfs driver is to expose thermal zone attributes as well
23as cooling device attributes to the user space.
24An intelligent thermal management application can make decisions based on inputs
25from thermal zone attributes (the current temperature and trip point temperature)
26and throttle appropriate devices.
27
28[0-*] denotes any positive number starting from 0
29[1-*] denotes any positive number starting from 1
30
311. thermal sysfs driver interface functions
32
331.1 thermal zone device interface
341.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name, int trips,
35 void *devdata, struct thermal_zone_device_ops *ops)
36
37 This interface function adds a new thermal zone device (sensor) to
38 /sys/class/thermal folder as thermal_zone[0-*].
39 It tries to bind all the thermal cooling devices registered at the same time.
40
41 name: the thermal zone name.
42 trips: the total number of trip points this thermal zone supports.
43 devdata: device private data
44 ops: thermal zone device callbacks.
45 .bind: bind the thermal zone device with a thermal cooling device.
46 .unbind: unbing the thermal zone device with a thermal cooling device.
47 .get_temp: get the current temperature of the thermal zone.
48 .get_mode: get the current mode (user/kernel) of the thermal zone.
49 "kernel" means thermal management is done in kernel.
50 "user" will prevent kernel thermal driver actions upon trip points
51 so that user applications can take charge of thermal management.
52 .set_mode: set the mode (user/kernel) of the thermal zone.
53 .get_trip_type: get the type of certain trip point.
54 .get_trip_temp: get the temperature above which the certain trip point
55 will be fired.
56
571.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
58
59 This interface function removes the thermal zone device.
60 It deletes the corresponding entry form /sys/class/thermal folder and unbind all
61 the thermal cooling devices it uses.
62
631.2 thermal cooling device interface
641.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
65 void *devdata, struct thermal_cooling_device_ops *)
66
67 This interface function adds a new thermal cooling device (fan/processor/...) to
68 /sys/class/thermal/ folder as cooling_device[0-*].
69 It tries to bind itself to all the thermal zone devices register at the same time.
70 name: the cooling device name.
71 devdata: device private data.
72 ops: thermal cooling devices callbacks.
73 .get_max_state: get the Maximum throttle state of the cooling device.
74 .get_cur_state: get the Current throttle state of the cooling device.
75 .set_cur_state: set the Current throttle state of the cooling device.
76
771.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
78
79 This interface function remove the thermal cooling device.
80 It deletes the corresponding entry form /sys/class/thermal folder and unbind
81 itself from all the thermal zone devices using it.
82
831.3 interface for binding a thermal zone device with a thermal cooling device
841.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
85 int trip, struct thermal_cooling_device *cdev);
86
87 This interface function bind a thermal cooling device to the certain trip point
88 of a thermal zone device.
89 This function is usually called in the thermal zone device .bind callback.
90 tz: the thermal zone device
91 cdev: thermal cooling device
92 trip: indicates which trip point the cooling devices is associated with
93 in this thermal zone.
94
951.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
96 int trip, struct thermal_cooling_device *cdev);
97
98 This interface function unbind a thermal cooling device from the certain trip point
99 of a thermal zone device.
100 This function is usually called in the thermal zone device .unbind callback.
101 tz: the thermal zone device
102 cdev: thermal cooling device
103 trip: indicates which trip point the cooling devices is associated with
104 in this thermal zone.
105
1062. sysfs attributes structure
107
108RO read only value
109RW read/write value
110
111All thermal sysfs attributes will be represented under /sys/class/thermal
112/sys/class/thermal/
113
114Thermal zone device sys I/F, created once it's registered:
115|thermal_zone[0-*]:
116 |-----type: Type of the thermal zone
117 |-----temp: Current temperature
118 |-----mode: Working mode of the thermal zone
119 |-----trip_point_[0-*]_temp: Trip point temperature
120 |-----trip_point_[0-*]_type: Trip point type
121
122Thermal cooling device sys I/F, created once it's registered:
123|cooling_device[0-*]:
124 |-----type : Type of the cooling device(processor/fan/...)
125 |-----max_state: Maximum cooling state of the cooling device
126 |-----cur_state: Current cooling state of the cooling device
127
128
129These two dynamic attributes are created/removed in pairs.
130They represent the relationship between a thermal zone and its associated cooling device.
131They are created/removed for each
132thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful exection.
133
134|thermal_zone[0-*]
135 |-----cdev[0-*]: The [0-*]th cooling device in the current thermal zone
136 |-----cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
137
138
139***************************
140* Thermal zone attributes *
141***************************
142
143type Strings which represent the thermal zone type.
144 This is given by thermal zone driver as part of registration.
145 Eg: "ACPI thermal zone" indicates it's a ACPI thermal device
146 RO
147 Optional
148
149temp Current temperature as reported by thermal zone (sensor)
150 Unit: degree celsius
151 RO
152 Required
153
154mode One of the predifned values in [kernel, user]
155 This file gives information about the algorithm
156 that is currently managing the thermal zone.
157 It can be either default kernel based algorithm
158 or user space application.
159 RW
160 Optional
161 kernel = Thermal management in kernel thermal zone driver.
162 user = Preventing kernel thermal zone driver actions upon
163 trip points so that user application can take full
164 charge of the thermal management.
165
166trip_point_[0-*]_temp The temperature above which trip point will be fired
167 Unit: degree celsius
168 RO
169 Optional
170
171trip_point_[0-*]_type Strings which indicate the type of the trip point
172 Eg. it can be one of critical, hot, passive,
173 active[0-*] for ACPI thermal zone.
174 RO
175 Optional
176
177cdev[0-*] Sysfs link to the thermal cooling device node where the sys I/F
178 for cooling device throttling control represents.
179 RO
180 Optional
181
182cdev[0-*]_trip_point The trip point with which cdev[0-*] is assocated in this thermal zone
183 -1 means the cooling device is not associated with any trip point.
184 RO
185 Optional
186
187******************************
188* Cooling device attributes *
189******************************
190
191type String which represents the type of device
192 eg: For generic ACPI: this should be "Fan",
193 "Processor" or "LCD"
194 eg. For memory controller device on intel_menlow platform:
195 this should be "Memory controller"
196 RO
197 Optional
198
199max_state The maximum permissible cooling state of this cooling device.
200 RO
201 Required
202
203cur_state The current cooling state of this cooling device.
204 the value can any integer numbers between 0 and max_state,
205 cur_state == 0 means no cooling
206 cur_state == max_state means the maximum cooling.
207 RW
208 Required
209
2103. A simple implementation
211
212ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
213If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
214it may register itself as a thermale_zone_device (thermal_zone1) with 4 trip points in all.
215It has one processor and one fan, which are both registered as thermal_cooling_device.
216If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
217the sys I/F structure will be built like this:
218
219/sys/class/thermal:
220
221|thermal_zone1:
222 |-----type: ACPI thermal zone
223 |-----temp: 37
224 |-----mode: kernel
225 |-----trip_point_0_temp: 100
226 |-----trip_point_0_type: critical
227 |-----trip_point_1_temp: 80
228 |-----trip_point_1_type: passive
229 |-----trip_point_2_temp: 70
230 |-----trip_point_2_type: active[0]
231 |-----trip_point_3_temp: 60
232 |-----trip_point_3_type: active[1]
233 |-----cdev0: --->/sys/class/thermal/cooling_device0
234 |-----cdev0_trip_point: 1 /* cdev0 can be used for passive */
235 |-----cdev1: --->/sys/class/thermal/cooling_device3
236 |-----cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
237
238|cooling_device0:
239 |-----type: Processor
240 |-----max_state: 8
241 |-----cur_state: 0
242
243|cooling_device3:
244 |-----type: Fan
245 |-----max_state: 2
246 |-----cur_state: 0
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