Root/Documentation/thermal/sysfs-api.txt

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
14devices (sensors) and thermal cooling devices (fan, processor...) to register
15with the thermal management solution and to be a part of it.
16
17This how-to focuses on enabling new thermal zone and cooling devices to
18participate in thermal management.
19This solution is platform independent and any type of thermal zone devices
20and cooling 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
23as well as cooling device attributes to the user space.
24An intelligent thermal management application can make decisions based on
25inputs from thermal zone attributes (the current temperature and trip point
26temperature) and 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,
35        int trips, 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-*]. It tries to bind all the
39    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 call-backs.
45    .bind: bind the thermal zone device with a thermal cooling device.
46    .unbind: unbind 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
61    unbind all 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/...)
68    to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
69    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 call-backs.
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
81    unbind 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
88    point 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
99    trip point of a thermal zone device. This function is usually called in
100    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
111Thermal sysfs attributes will be represented under /sys/class/thermal.
112Hwmon sysfs I/F extension is also available under /sys/class/hwmon
113if hwmon is compiled in or built as a module.
114
115Thermal zone device sys I/F, created once it's registered:
116/sys/class/thermal/thermal_zone[0-*]:
117    |---type: Type of the thermal zone
118    |---temp: Current temperature
119    |---mode: Working mode of the thermal zone
120    |---trip_point_[0-*]_temp: Trip point temperature
121    |---trip_point_[0-*]_type: Trip point type
122
123Thermal cooling device sys I/F, created once it's registered:
124/sys/class/thermal/cooling_device[0-*]:
125    |---type: Type of the cooling device(processor/fan/...)
126    |---max_state: Maximum cooling state of the cooling device
127    |---cur_state: Current cooling state of the cooling device
128
129
130Then next two dynamic attributes are created/removed in pairs. They represent
131the relationship between a thermal zone and its associated cooling device.
132They are created/removed for each successful execution of
133thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
134
135/sys/class/thermal/thermal_zone[0-*]:
136    |---cdev[0-*]: [0-*]th cooling device in current thermal zone
137    |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
138
139Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
140the generic thermal driver also creates a hwmon sysfs I/F for each _type_
141of thermal zone device. E.g. the generic thermal driver registers one hwmon
142class device and build the associated hwmon sysfs I/F for all the registered
143ACPI thermal zones.
144
145/sys/class/hwmon/hwmon[0-*]:
146    |---name: The type of the thermal zone devices
147    |---temp[1-*]_input: The current temperature of thermal zone [1-*]
148    |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
149
150Please read Documentation/hwmon/sysfs-interface for additional information.
151
152***************************
153* Thermal zone attributes *
154***************************
155
156type
157    Strings which represent the thermal zone type.
158    This is given by thermal zone driver as part of registration.
159    E.g: "acpitz" indicates it's an ACPI thermal device.
160    In order to keep it consistent with hwmon sys attribute; this should
161    be a short, lowercase string, not containing spaces nor dashes.
162    RO, Required
163
164temp
165    Current temperature as reported by thermal zone (sensor).
166    Unit: millidegree Celsius
167    RO, Required
168
169mode
170    One of the predefined values in [kernel, user].
171    This file gives information about the algorithm that is currently
172    managing the thermal zone. It can be either default kernel based
173    algorithm or user space application.
174    kernel = Thermal management in kernel thermal zone driver.
175    user = Preventing kernel thermal zone driver actions upon
176          trip points so that user application can take full
177          charge of the thermal management.
178    RW, Optional
179
180trip_point_[0-*]_temp
181    The temperature above which trip point will be fired.
182    Unit: millidegree Celsius
183    RO, Optional
184
185trip_point_[0-*]_type
186    Strings which indicate the type of the trip point.
187    E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
188    thermal zone.
189    RO, Optional
190
191cdev[0-*]
192    Sysfs link to the thermal cooling device node where the sys I/F
193    for cooling device throttling control represents.
194    RO, Optional
195
196cdev[0-*]_trip_point
197    The trip point with which cdev[0-*] is associated in this thermal
198    zone; -1 means the cooling device is not associated with any trip
199    point.
200    RO, Optional
201
202passive
203    Attribute is only present for zones in which the passive cooling
204    policy is not supported by native thermal driver. Default is zero
205    and can be set to a temperature (in millidegrees) to enable a
206    passive trip point for the zone. Activation is done by polling with
207    an interval of 1 second.
208    Unit: millidegrees Celsius
209    Valid values: 0 (disabled) or greater than 1000
210    RW, Optional
211
212*****************************
213* Cooling device attributes *
214*****************************
215
216type
217    String which represents the type of device, e.g:
218    - for generic ACPI: should be "Fan", "Processor" or "LCD"
219    - for memory controller device on intel_menlow platform:
220      should be "Memory controller".
221    RO, Required
222
223max_state
224    The maximum permissible cooling state of this cooling device.
225    RO, Required
226
227cur_state
228    The current cooling state of this cooling device.
229    The value can any integer numbers between 0 and max_state:
230    - cur_state == 0 means no cooling
231    - cur_state == max_state means the maximum cooling.
232    RW, Required
233
2343. A simple implementation
235
236ACPI thermal zone may support multiple trip points like critical, hot,
237passive, active. If an ACPI thermal zone supports critical, passive,
238active[0] and active[1] at the same time, it may register itself as a
239thermal_zone_device (thermal_zone1) with 4 trip points in all.
240It has one processor and one fan, which are both registered as
241thermal_cooling_device.
242
243If the processor is listed in _PSL method, and the fan is listed in _AL0
244method, the sys I/F structure will be built like this:
245
246/sys/class/thermal:
247
248|thermal_zone1:
249    |---type: acpitz
250    |---temp: 37000
251    |---mode: kernel
252    |---trip_point_0_temp: 100000
253    |---trip_point_0_type: critical
254    |---trip_point_1_temp: 80000
255    |---trip_point_1_type: passive
256    |---trip_point_2_temp: 70000
257    |---trip_point_2_type: active0
258    |---trip_point_3_temp: 60000
259    |---trip_point_3_type: active1
260    |---cdev0: --->/sys/class/thermal/cooling_device0
261    |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
262    |---cdev1: --->/sys/class/thermal/cooling_device3
263    |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
264
265|cooling_device0:
266    |---type: Processor
267    |---max_state: 8
268    |---cur_state: 0
269
270|cooling_device3:
271    |---type: Fan
272    |---max_state: 2
273    |---cur_state: 0
274
275/sys/class/hwmon:
276
277|hwmon0:
278    |---name: acpitz
279    |---temp1_input: 37000
280    |---temp1_crit: 100000
281
2824. Event Notification
283
284The framework includes a simple notification mechanism, in the form of a
285netlink event. Netlink socket initialization is done during the _init_
286of the framework. Drivers which intend to use the notification mechanism
287just need to call generate_netlink_event() with two arguments viz
288(originator, event). Typically the originator will be an integer assigned
289to a thermal_zone_device when it registers itself with the framework. The
290event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
291THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
292crosses any of the configured thresholds.
293

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