sysfs-api.txt 16 KB

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  1. Generic Thermal Sysfs driver How To
  2. ===================================
  3. Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
  4. Updated: 2 January 2008
  5. Copyright (c) 2008 Intel Corporation
  6. 0. Introduction
  7. The generic thermal sysfs provides a set of interfaces for thermal zone
  8. devices (sensors) and thermal cooling devices (fan, processor...) to register
  9. with the thermal management solution and to be a part of it.
  10. This how-to focuses on enabling new thermal zone and cooling devices to
  11. participate in thermal management.
  12. This solution is platform independent and any type of thermal zone devices
  13. and cooling devices should be able to make use of the infrastructure.
  14. The main task of the thermal sysfs driver is to expose thermal zone attributes
  15. as well as cooling device attributes to the user space.
  16. An intelligent thermal management application can make decisions based on
  17. inputs from thermal zone attributes (the current temperature and trip point
  18. temperature) and throttle appropriate devices.
  19. [0-*] denotes any positive number starting from 0
  20. [1-*] denotes any positive number starting from 1
  21. 1. thermal sysfs driver interface functions
  22. 1.1 thermal zone device interface
  23. 1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *type,
  24. int trips, int mask, void *devdata,
  25. struct thermal_zone_device_ops *ops,
  26. const struct thermal_zone_params *tzp,
  27. int passive_delay, int polling_delay))
  28. This interface function adds a new thermal zone device (sensor) to
  29. /sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
  30. thermal cooling devices registered at the same time.
  31. type: the thermal zone type.
  32. trips: the total number of trip points this thermal zone supports.
  33. mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
  34. devdata: device private data
  35. ops: thermal zone device call-backs.
  36. .bind: bind the thermal zone device with a thermal cooling device.
  37. .unbind: unbind the thermal zone device with a thermal cooling device.
  38. .get_temp: get the current temperature of the thermal zone.
  39. .get_mode: get the current mode (enabled/disabled) of the thermal zone.
  40. - "enabled" means the kernel thermal management is enabled.
  41. - "disabled" will prevent kernel thermal driver action upon trip points
  42. so that user applications can take charge of thermal management.
  43. .set_mode: set the mode (enabled/disabled) of the thermal zone.
  44. .get_trip_type: get the type of certain trip point.
  45. .get_trip_temp: get the temperature above which the certain trip point
  46. will be fired.
  47. .set_emul_temp: set the emulation temperature which helps in debugging
  48. different threshold temperature points.
  49. tzp: thermal zone platform parameters.
  50. passive_delay: number of milliseconds to wait between polls when
  51. performing passive cooling.
  52. polling_delay: number of milliseconds to wait between polls when checking
  53. whether trip points have been crossed (0 for interrupt driven systems).
  54. 1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
  55. This interface function removes the thermal zone device.
  56. It deletes the corresponding entry form /sys/class/thermal folder and
  57. unbind all the thermal cooling devices it uses.
  58. 1.2 thermal cooling device interface
  59. 1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
  60. void *devdata, struct thermal_cooling_device_ops *)
  61. This interface function adds a new thermal cooling device (fan/processor/...)
  62. to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
  63. to all the thermal zone devices register at the same time.
  64. name: the cooling device name.
  65. devdata: device private data.
  66. ops: thermal cooling devices call-backs.
  67. .get_max_state: get the Maximum throttle state of the cooling device.
  68. .get_cur_state: get the Current throttle state of the cooling device.
  69. .set_cur_state: set the Current throttle state of the cooling device.
  70. 1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
  71. This interface function remove the thermal cooling device.
  72. It deletes the corresponding entry form /sys/class/thermal folder and
  73. unbind itself from all the thermal zone devices using it.
  74. 1.3 interface for binding a thermal zone device with a thermal cooling device
  75. 1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
  76. int trip, struct thermal_cooling_device *cdev,
  77. unsigned long upper, unsigned long lower);
  78. This interface function bind a thermal cooling device to the certain trip
  79. point of a thermal zone device.
  80. This function is usually called in the thermal zone device .bind callback.
  81. tz: the thermal zone device
  82. cdev: thermal cooling device
  83. trip: indicates which trip point the cooling devices is associated with
  84. in this thermal zone.
  85. upper:the Maximum cooling state for this trip point.
  86. THERMAL_NO_LIMIT means no upper limit,
  87. and the cooling device can be in max_state.
  88. lower:the Minimum cooling state can be used for this trip point.
  89. THERMAL_NO_LIMIT means no lower limit,
  90. and the cooling device can be in cooling state 0.
  91. 1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
  92. int trip, struct thermal_cooling_device *cdev);
  93. This interface function unbind a thermal cooling device from the certain
  94. trip point of a thermal zone device. This function is usually called in
  95. the thermal zone device .unbind callback.
  96. tz: the thermal zone device
  97. cdev: thermal cooling device
  98. trip: indicates which trip point the cooling devices is associated with
  99. in this thermal zone.
  100. 1.4 Thermal Zone Parameters
  101. 1.4.1 struct thermal_bind_params
  102. This structure defines the following parameters that are used to bind
  103. a zone with a cooling device for a particular trip point.
  104. .cdev: The cooling device pointer
  105. .weight: The 'influence' of a particular cooling device on this zone.
  106. This is on a percentage scale. The sum of all these weights
  107. (for a particular zone) cannot exceed 100.
  108. .trip_mask:This is a bit mask that gives the binding relation between
  109. this thermal zone and cdev, for a particular trip point.
  110. If nth bit is set, then the cdev and thermal zone are bound
  111. for trip point n.
  112. .match: This call back returns success(0) if the 'tz and cdev' need to
  113. be bound, as per platform data.
  114. 1.4.2 struct thermal_zone_params
  115. This structure defines the platform level parameters for a thermal zone.
  116. This data, for each thermal zone should come from the platform layer.
  117. This is an optional feature where some platforms can choose not to
  118. provide this data.
  119. .governor_name: Name of the thermal governor used for this zone
  120. .num_tbps: Number of thermal_bind_params entries for this zone
  121. .tbp: thermal_bind_params entries
  122. 2. sysfs attributes structure
  123. RO read only value
  124. RW read/write value
  125. Thermal sysfs attributes will be represented under /sys/class/thermal.
  126. Hwmon sysfs I/F extension is also available under /sys/class/hwmon
  127. if hwmon is compiled in or built as a module.
  128. Thermal zone device sys I/F, created once it's registered:
  129. /sys/class/thermal/thermal_zone[0-*]:
  130. |---type: Type of the thermal zone
  131. |---temp: Current temperature
  132. |---mode: Working mode of the thermal zone
  133. |---policy: Thermal governor used for this zone
  134. |---trip_point_[0-*]_temp: Trip point temperature
  135. |---trip_point_[0-*]_type: Trip point type
  136. |---trip_point_[0-*]_hyst: Hysteresis value for this trip point
  137. |---emul_temp: Emulated temperature set node
  138. Thermal cooling device sys I/F, created once it's registered:
  139. /sys/class/thermal/cooling_device[0-*]:
  140. |---type: Type of the cooling device(processor/fan/...)
  141. |---max_state: Maximum cooling state of the cooling device
  142. |---cur_state: Current cooling state of the cooling device
  143. Then next two dynamic attributes are created/removed in pairs. They represent
  144. the relationship between a thermal zone and its associated cooling device.
  145. They are created/removed for each successful execution of
  146. thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
  147. /sys/class/thermal/thermal_zone[0-*]:
  148. |---cdev[0-*]: [0-*]th cooling device in current thermal zone
  149. |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
  150. Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
  151. the generic thermal driver also creates a hwmon sysfs I/F for each _type_
  152. of thermal zone device. E.g. the generic thermal driver registers one hwmon
  153. class device and build the associated hwmon sysfs I/F for all the registered
  154. ACPI thermal zones.
  155. /sys/class/hwmon/hwmon[0-*]:
  156. |---name: The type of the thermal zone devices
  157. |---temp[1-*]_input: The current temperature of thermal zone [1-*]
  158. |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
  159. Please read Documentation/hwmon/sysfs-interface for additional information.
  160. ***************************
  161. * Thermal zone attributes *
  162. ***************************
  163. type
  164. Strings which represent the thermal zone type.
  165. This is given by thermal zone driver as part of registration.
  166. E.g: "acpitz" indicates it's an ACPI thermal device.
  167. In order to keep it consistent with hwmon sys attribute; this should
  168. be a short, lowercase string, not containing spaces nor dashes.
  169. RO, Required
  170. temp
  171. Current temperature as reported by thermal zone (sensor).
  172. Unit: millidegree Celsius
  173. RO, Required
  174. mode
  175. One of the predefined values in [enabled, disabled].
  176. This file gives information about the algorithm that is currently
  177. managing the thermal zone. It can be either default kernel based
  178. algorithm or user space application.
  179. enabled = enable Kernel Thermal management.
  180. disabled = Preventing kernel thermal zone driver actions upon
  181. trip points so that user application can take full
  182. charge of the thermal management.
  183. RW, Optional
  184. policy
  185. One of the various thermal governors used for a particular zone.
  186. RW, Required
  187. trip_point_[0-*]_temp
  188. The temperature above which trip point will be fired.
  189. Unit: millidegree Celsius
  190. RO, Optional
  191. trip_point_[0-*]_type
  192. Strings which indicate the type of the trip point.
  193. E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
  194. thermal zone.
  195. RO, Optional
  196. trip_point_[0-*]_hyst
  197. The hysteresis value for a trip point, represented as an integer
  198. Unit: Celsius
  199. RW, Optional
  200. cdev[0-*]
  201. Sysfs link to the thermal cooling device node where the sys I/F
  202. for cooling device throttling control represents.
  203. RO, Optional
  204. cdev[0-*]_trip_point
  205. The trip point with which cdev[0-*] is associated in this thermal
  206. zone; -1 means the cooling device is not associated with any trip
  207. point.
  208. RO, Optional
  209. passive
  210. Attribute is only present for zones in which the passive cooling
  211. policy is not supported by native thermal driver. Default is zero
  212. and can be set to a temperature (in millidegrees) to enable a
  213. passive trip point for the zone. Activation is done by polling with
  214. an interval of 1 second.
  215. Unit: millidegrees Celsius
  216. Valid values: 0 (disabled) or greater than 1000
  217. RW, Optional
  218. emul_temp
  219. Interface to set the emulated temperature method in thermal zone
  220. (sensor). After setting this temperature, the thermal zone may pass
  221. this temperature to platform emulation function if registered or
  222. cache it locally. This is useful in debugging different temperature
  223. threshold and its associated cooling action. This is write only node
  224. and writing 0 on this node should disable emulation.
  225. Unit: millidegree Celsius
  226. WO, Optional
  227. WARNING: Be careful while enabling this option on production systems,
  228. because userland can easily disable the thermal policy by simply
  229. flooding this sysfs node with low temperature values.
  230. *****************************
  231. * Cooling device attributes *
  232. *****************************
  233. type
  234. String which represents the type of device, e.g:
  235. - for generic ACPI: should be "Fan", "Processor" or "LCD"
  236. - for memory controller device on intel_menlow platform:
  237. should be "Memory controller".
  238. RO, Required
  239. max_state
  240. The maximum permissible cooling state of this cooling device.
  241. RO, Required
  242. cur_state
  243. The current cooling state of this cooling device.
  244. The value can any integer numbers between 0 and max_state:
  245. - cur_state == 0 means no cooling
  246. - cur_state == max_state means the maximum cooling.
  247. RW, Required
  248. 3. A simple implementation
  249. ACPI thermal zone may support multiple trip points like critical, hot,
  250. passive, active. If an ACPI thermal zone supports critical, passive,
  251. active[0] and active[1] at the same time, it may register itself as a
  252. thermal_zone_device (thermal_zone1) with 4 trip points in all.
  253. It has one processor and one fan, which are both registered as
  254. thermal_cooling_device.
  255. If the processor is listed in _PSL method, and the fan is listed in _AL0
  256. method, the sys I/F structure will be built like this:
  257. /sys/class/thermal:
  258. |thermal_zone1:
  259. |---type: acpitz
  260. |---temp: 37000
  261. |---mode: enabled
  262. |---policy: step_wise
  263. |---trip_point_0_temp: 100000
  264. |---trip_point_0_type: critical
  265. |---trip_point_1_temp: 80000
  266. |---trip_point_1_type: passive
  267. |---trip_point_2_temp: 70000
  268. |---trip_point_2_type: active0
  269. |---trip_point_3_temp: 60000
  270. |---trip_point_3_type: active1
  271. |---cdev0: --->/sys/class/thermal/cooling_device0
  272. |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
  273. |---cdev1: --->/sys/class/thermal/cooling_device3
  274. |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
  275. |cooling_device0:
  276. |---type: Processor
  277. |---max_state: 8
  278. |---cur_state: 0
  279. |cooling_device3:
  280. |---type: Fan
  281. |---max_state: 2
  282. |---cur_state: 0
  283. /sys/class/hwmon:
  284. |hwmon0:
  285. |---name: acpitz
  286. |---temp1_input: 37000
  287. |---temp1_crit: 100000
  288. 4. Event Notification
  289. The framework includes a simple notification mechanism, in the form of a
  290. netlink event. Netlink socket initialization is done during the _init_
  291. of the framework. Drivers which intend to use the notification mechanism
  292. just need to call thermal_generate_netlink_event() with two arguments viz
  293. (originator, event). The originator is a pointer to struct thermal_zone_device
  294. from where the event has been originated. An integer which represents the
  295. thermal zone device will be used in the message to identify the zone. The
  296. event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
  297. THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
  298. crosses any of the configured thresholds.
  299. 5. Export Symbol APIs:
  300. 5.1: get_tz_trend:
  301. This function returns the trend of a thermal zone, i.e the rate of change
  302. of temperature of the thermal zone. Ideally, the thermal sensor drivers
  303. are supposed to implement the callback. If they don't, the thermal
  304. framework calculated the trend by comparing the previous and the current
  305. temperature values.
  306. 5.2:get_thermal_instance:
  307. This function returns the thermal_instance corresponding to a given
  308. {thermal_zone, cooling_device, trip_point} combination. Returns NULL
  309. if such an instance does not exist.
  310. 5.3:thermal_notify_framework:
  311. This function handles the trip events from sensor drivers. It starts
  312. throttling the cooling devices according to the policy configured.
  313. For CRITICAL and HOT trip points, this notifies the respective drivers,
  314. and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
  315. The throttling policy is based on the configured platform data; if no
  316. platform data is provided, this uses the step_wise throttling policy.
  317. 5.4:thermal_cdev_update:
  318. This function serves as an arbitrator to set the state of a cooling
  319. device. It sets the cooling device to the deepest cooling state if
  320. possible.