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 *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)) 39 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. 43 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). 67 68 691.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz) 70 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. 74 751.2 thermal cooling device interface 761.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name, 77 void *devdata, struct thermal_cooling_device_ops *) 78 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. 88 891.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev) 90 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. 94 951.3 interface for binding a thermal zone device with a thermal cooling device 961.3.1 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); 99 100 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. 113 1141.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz, 115 int trip, struct thermal_cooling_device *cdev); 116 117 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. 124 1251.4 Thermal Zone Parameters 1261.4.1 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. 1461.4.2 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 159 1602. sysfs attributes structure 161 162RO read only value 163RW read/write value 164 165Thermal sysfs attributes will be represented under /sys/class/thermal. 166Hwmon sysfs I/F extension is also available under /sys/class/hwmon 167if hwmon is compiled in or built as a module. 168 169Thermal 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 179 180Thermal 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 185 186 187Then next two dynamic attributes are created/removed in pairs. They represent 188the relationship between a thermal zone and its associated cooling device. 189They are created/removed for each successful execution of 190thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device. 191 192/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 195 196Besides the thermal zone device sysfs I/F and cooling device sysfs I/F, 197the generic thermal driver also creates a hwmon sysfs I/F for each _type_ 198of thermal zone device. E.g. the generic thermal driver registers one hwmon 199class device and build the associated hwmon sysfs I/F for all the registered 200ACPI thermal zones. 201 202/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-*] 206 207Please read Documentation/hwmon/sysfs-interface for additional information. 208 209*************************** 210* Thermal zone attributes * 211*************************** 212 213type 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 220 221temp 222 Current temperature as reported by thermal zone (sensor). 223 Unit: millidegree Celsius 224 RO, Required 225 226mode 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 236 237policy 238 One of the various thermal governors used for a particular zone. 239 RW, Required 240 241trip_point_[0-*]_temp 242 The temperature above which trip point will be fired. 243 Unit: millidegree Celsius 244 RO, Optional 245 246trip_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 251 252trip_point_[0-*]_hyst 253 The hysteresis value for a trip point, represented as an integer 254 Unit: Celsius 255 RW, Optional 256 257cdev[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 261 262cdev[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 267 268passive 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 277 278emul_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 287 288 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. 291 292***************************** 293* Cooling device attributes * 294***************************** 295 296type 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 302 303max_state 304 The maximum permissible cooling state of this cooling device. 305 RO, Required 306 307cur_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 313 3143. A simple implementation 315 316ACPI thermal zone may support multiple trip points like critical, hot, 317passive, active. If an ACPI thermal zone supports critical, passive, 318active[0] and active[1] at the same time, it may register itself as a 319thermal_zone_device (thermal_zone1) with 4 trip points in all. 320It has one processor and one fan, which are both registered as 321thermal_cooling_device. 322 323If the processor is listed in _PSL method, and the fan is listed in _AL0 324method, the sys I/F structure will be built like this: 325 326/sys/class/thermal: 327 328|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]*/ 345 346|cooling_device0: 347 |---type: Processor 348 |---max_state: 8 349 |---cur_state: 0 350 351|cooling_device3: 352 |---type: Fan 353 |---max_state: 2 354 |---cur_state: 0 355 356/sys/class/hwmon: 357 358|hwmon0: 359 |---name: acpitz 360 |---temp1_input: 37000 361 |---temp1_crit: 100000 362 3634. Event Notification 364 365The framework includes a simple notification mechanism, in the form of a 366netlink event. Netlink socket initialization is done during the _init_ 367of the framework. Drivers which intend to use the notification mechanism 368just need to call thermal_generate_netlink_event() with two arguments viz 369(originator, event). The originator is a pointer to struct thermal_zone_device 370from where the event has been originated. An integer which represents the 371thermal zone device will be used in the message to identify the zone. The 372event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL, 373THERMAL_DEV_FAULT}. Notification can be sent when the current temperature 374crosses any of the configured thresholds. 375 3765. Export Symbol APIs: 377 3785.1: get_tz_trend: 379This function returns the trend of a thermal zone, i.e the rate of change 380of temperature of the thermal zone. Ideally, the thermal sensor drivers 381are supposed to implement the callback. If they don't, the thermal 382framework calculated the trend by comparing the previous and the current 383temperature values. 384 3855.2:get_thermal_instance: 386This function returns the thermal_instance corresponding to a given 387{thermal_zone, cooling_device, trip_point} combination. Returns NULL 388if such an instance does not exist. 389 3905.3:thermal_notify_framework: 391This function handles the trip events from sensor drivers. It starts 392throttling the cooling devices according to the policy configured. 393For CRITICAL and HOT trip points, this notifies the respective drivers, 394and does actual throttling for other trip points i.e ACTIVE and PASSIVE. 395The throttling policy is based on the configured platform data; if no 396platform data is provided, this uses the step_wise throttling policy. 397 3985.4:thermal_cdev_update: 399This function serves as an arbitrator to set the state of a cooling 400device. It sets the cooling device to the deepest cooling state if 401possible. 402