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
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 *name,
35 int trips, int mask, void *devdata,
36 struct thermal_zone_device_ops *ops)
38 This interface function adds a new thermal zone device (sensor) to
39 /sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
40 thermal cooling devices registered at the same time.
42 name: the thermal zone name.
43 trips: the total number of trip points this thermal zone supports.
44 mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
45 devdata: device private data
46 ops: thermal zone device call-backs.
47 .bind: bind the thermal zone device with a thermal cooling device.
48 .unbind: unbind the thermal zone device with a thermal cooling device.
49 .get_temp: get the current temperature of the thermal zone.
50 .get_mode: get the current mode (user/kernel) of the thermal zone.
51 - "kernel" means thermal management is done in kernel.
52 - "user" will prevent kernel thermal driver actions upon trip points
53 so that user applications can take charge of thermal management.
54 .set_mode: set the mode (user/kernel) of the thermal zone.
55 .get_trip_type: get the type of certain trip point.
56 .get_trip_temp: get the temperature above which the certain trip point
59 1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
61 This interface function removes the thermal zone device.
62 It deletes the corresponding entry form /sys/class/thermal folder and
63 unbind all the thermal cooling devices it uses.
65 1.2 thermal cooling device interface
66 1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
67 void *devdata, struct thermal_cooling_device_ops *)
69 This interface function adds a new thermal cooling device (fan/processor/...)
70 to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
71 to all the thermal zone devices register at the same time.
72 name: the cooling device name.
73 devdata: device private data.
74 ops: thermal cooling devices call-backs.
75 .get_max_state: get the Maximum throttle state of the cooling device.
76 .get_cur_state: get the Current throttle state of the cooling device.
77 .set_cur_state: set the Current throttle state of the cooling device.
79 1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
81 This interface function remove the thermal cooling device.
82 It deletes the corresponding entry form /sys/class/thermal folder and
83 unbind itself from all the thermal zone devices using it.
85 1.3 interface for binding a thermal zone device with a thermal cooling device
86 1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
87 int trip, struct thermal_cooling_device *cdev);
89 This interface function bind a thermal cooling device to the certain trip
90 point of a thermal zone device.
91 This function is usually called in the thermal zone device .bind callback.
92 tz: the thermal zone device
93 cdev: thermal cooling device
94 trip: indicates which trip point the cooling devices is associated with
97 1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
98 int trip, struct thermal_cooling_device *cdev);
100 This interface function unbind a thermal cooling device from the certain
101 trip point of a thermal zone device. This function is usually called in
102 the thermal zone device .unbind 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.
108 2. sysfs attributes structure
113 Thermal sysfs attributes will be represented under /sys/class/thermal.
114 Hwmon sysfs I/F extension is also available under /sys/class/hwmon
115 if hwmon is compiled in or built as a module.
117 Thermal zone device sys I/F, created once it's registered:
118 /sys/class/thermal/thermal_zone[0-*]:
119 |---type: Type of the thermal zone
120 |---temp: Current temperature
121 |---mode: Working mode of the thermal zone
122 |---trip_point_[0-*]_temp: Trip point temperature
123 |---trip_point_[0-*]_type: Trip point type
125 Thermal cooling device sys I/F, created once it's registered:
126 /sys/class/thermal/cooling_device[0-*]:
127 |---type: Type of the cooling device(processor/fan/...)
128 |---max_state: Maximum cooling state of the cooling device
129 |---cur_state: Current cooling state of the cooling device
132 Then next two dynamic attributes are created/removed in pairs. They represent
133 the relationship between a thermal zone and its associated cooling device.
134 They are created/removed for each successful execution of
135 thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
137 /sys/class/thermal/thermal_zone[0-*]:
138 |---cdev[0-*]: [0-*]th cooling device in current thermal zone
139 |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
141 Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
142 the generic thermal driver also creates a hwmon sysfs I/F for each _type_
143 of thermal zone device. E.g. the generic thermal driver registers one hwmon
144 class device and build the associated hwmon sysfs I/F for all the registered
147 /sys/class/hwmon/hwmon[0-*]:
148 |---name: The type of the thermal zone devices
149 |---temp[1-*]_input: The current temperature of thermal zone [1-*]
150 |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
152 Please read Documentation/hwmon/sysfs-interface for additional information.
154 ***************************
155 * Thermal zone attributes *
156 ***************************
159 Strings which represent the thermal zone type.
160 This is given by thermal zone driver as part of registration.
161 E.g: "acpitz" indicates it's an ACPI thermal device.
162 In order to keep it consistent with hwmon sys attribute; this should
163 be a short, lowercase string, not containing spaces nor dashes.
167 Current temperature as reported by thermal zone (sensor).
168 Unit: millidegree Celsius
172 One of the predefined values in [kernel, user].
173 This file gives information about the algorithm that is currently
174 managing the thermal zone. It can be either default kernel based
175 algorithm or user space application.
176 kernel = Thermal management in kernel thermal zone driver.
177 user = Preventing kernel thermal zone driver actions upon
178 trip points so that user application can take full
179 charge of the thermal management.
182 trip_point_[0-*]_temp
183 The temperature above which trip point will be fired.
184 Unit: millidegree Celsius
187 trip_point_[0-*]_type
188 Strings which indicate the type of the trip point.
189 E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
194 Sysfs link to the thermal cooling device node where the sys I/F
195 for cooling device throttling control represents.
199 The trip point with which cdev[0-*] is associated in this thermal
200 zone; -1 means the cooling device is not associated with any trip
205 Attribute is only present for zones in which the passive cooling
206 policy is not supported by native thermal driver. Default is zero
207 and can be set to a temperature (in millidegrees) to enable a
208 passive trip point for the zone. Activation is done by polling with
209 an interval of 1 second.
210 Unit: millidegrees Celsius
211 Valid values: 0 (disabled) or greater than 1000
214 *****************************
215 * Cooling device attributes *
216 *****************************
219 String which represents the type of device, e.g:
220 - for generic ACPI: should be "Fan", "Processor" or "LCD"
221 - for memory controller device on intel_menlow platform:
222 should be "Memory controller".
226 The maximum permissible cooling state of this cooling device.
230 The current cooling state of this cooling device.
231 The value can any integer numbers between 0 and max_state:
232 - cur_state == 0 means no cooling
233 - cur_state == max_state means the maximum cooling.
236 3. A simple implementation
238 ACPI thermal zone may support multiple trip points like critical, hot,
239 passive, active. If an ACPI thermal zone supports critical, passive,
240 active[0] and active[1] at the same time, it may register itself as a
241 thermal_zone_device (thermal_zone1) with 4 trip points in all.
242 It has one processor and one fan, which are both registered as
243 thermal_cooling_device.
245 If the processor is listed in _PSL method, and the fan is listed in _AL0
246 method, the sys I/F structure will be built like this:
254 |---trip_point_0_temp: 100000
255 |---trip_point_0_type: critical
256 |---trip_point_1_temp: 80000
257 |---trip_point_1_type: passive
258 |---trip_point_2_temp: 70000
259 |---trip_point_2_type: active0
260 |---trip_point_3_temp: 60000
261 |---trip_point_3_type: active1
262 |---cdev0: --->/sys/class/thermal/cooling_device0
263 |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
264 |---cdev1: --->/sys/class/thermal/cooling_device3
265 |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
281 |---temp1_input: 37000
282 |---temp1_crit: 100000
284 4. Event Notification
286 The framework includes a simple notification mechanism, in the form of a
287 netlink event. Netlink socket initialization is done during the _init_
288 of the framework. Drivers which intend to use the notification mechanism
289 just need to call thermal_generate_netlink_event() with two arguments viz
290 (originator, event). Typically the originator will be an integer assigned
291 to a thermal_zone_device when it registers itself with the framework. The
292 event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
293 THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
294 crosses any of the configured thresholds.