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authorZhang Rui <rui.zhang@intel.com>2008-01-17 15:51:08 +0800
committerLen Brown <len.brown@intel.com>2008-02-01 23:12:19 -0500
commit203d3d4aa482339b4816f131f713e1b8ee37f6dd (patch)
treede7f27619e88ca6bf62bbba21fb54f213a98394a /Documentation
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downloadlinux-linaro-android-203d3d4aa482339b4816f131f713e1b8ee37f6dd.tar.gz
the generic thermal sysfs driver
The Generic Thermal sysfs driver for thermal management. Signed-off-by: Zhang Rui <rui.zhang@intel.com> Signed-off-by: Thomas Sujith <sujith.thomas@intel.com> Signed-off-by: Len Brown <len.brown@intel.com>
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+Generic Thermal Sysfs driver How To
+=========================
+
+Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
+
+Updated: 2 January 2008
+
+Copyright (c) 2008 Intel Corporation
+
+
+0. Introduction
+
+The generic thermal sysfs provides a set of interfaces for thermal zone devices (sensors)
+and thermal cooling devices (fan, processor...) to register with the thermal management
+solution and to be a part of it.
+
+This how-to focusses on enabling new thermal zone and cooling devices to participate
+in thermal management.
+This solution is platform independent and any type of thermal zone devices and
+cooling devices should be able to make use of the infrastructure.
+
+The main task of the thermal sysfs driver is to expose thermal zone attributes as well
+as cooling device attributes to the user space.
+An intelligent thermal management application can make decisions based on inputs
+from thermal zone attributes (the current temperature and trip point temperature)
+and throttle appropriate devices.
+
+[0-*] denotes any positive number starting from 0
+[1-*] denotes any positive number starting from 1
+
+1. thermal sysfs driver interface functions
+
+1.1 thermal zone device interface
+1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name, int trips,
+ void *devdata, struct thermal_zone_device_ops *ops)
+
+ This interface function adds a new thermal zone device (sensor) to
+ /sys/class/thermal folder as thermal_zone[0-*].
+ It tries to bind all the thermal cooling devices registered at the same time.
+
+ name: the thermal zone name.
+ trips: the total number of trip points this thermal zone supports.
+ devdata: device private data
+ ops: thermal zone device callbacks.
+ .bind: bind the thermal zone device with a thermal cooling device.
+ .unbind: unbing the thermal zone device with a thermal cooling device.
+ .get_temp: get the current temperature of the thermal zone.
+ .get_mode: get the current mode (user/kernel) of the thermal zone.
+ "kernel" means thermal management is done in kernel.
+ "user" will prevent kernel thermal driver actions upon trip points
+ so that user applications can take charge of thermal management.
+ .set_mode: set the mode (user/kernel) of the thermal zone.
+ .get_trip_type: get the type of certain trip point.
+ .get_trip_temp: get the temperature above which the certain trip point
+ will be fired.
+
+1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
+
+ This interface function removes the thermal zone device.
+ It deletes the corresponding entry form /sys/class/thermal folder and unbind all
+ the thermal cooling devices it uses.
+
+1.2 thermal cooling device interface
+1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
+ void *devdata, struct thermal_cooling_device_ops *)
+
+ This interface function adds a new thermal cooling device (fan/processor/...) to
+ /sys/class/thermal/ folder as cooling_device[0-*].
+ It tries to bind itself to all the thermal zone devices register at the same time.
+ name: the cooling device name.
+ devdata: device private data.
+ ops: thermal cooling devices callbacks.
+ .get_max_state: get the Maximum throttle state of the cooling device.
+ .get_cur_state: get the Current throttle state of the cooling device.
+ .set_cur_state: set the Current throttle state of the cooling device.
+
+1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
+
+ This interface function remove the thermal cooling device.
+ It deletes the corresponding entry form /sys/class/thermal folder and unbind
+ itself from all the thermal zone devices using it.
+
+1.3 interface for binding a thermal zone device with a thermal cooling device
+1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
+ int trip, struct thermal_cooling_device *cdev);
+
+ This interface function bind a thermal cooling device to the certain trip point
+ of a thermal zone device.
+ This function is usually called in the thermal zone device .bind callback.
+ tz: the thermal zone device
+ cdev: thermal cooling device
+ trip: indicates which trip point the cooling devices is associated with
+ in this thermal zone.
+
+1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
+ int trip, struct thermal_cooling_device *cdev);
+
+ This interface function unbind a thermal cooling device from the certain trip point
+ of a thermal zone device.
+ This function is usually called in the thermal zone device .unbind callback.
+ tz: the thermal zone device
+ cdev: thermal cooling device
+ trip: indicates which trip point the cooling devices is associated with
+ in this thermal zone.
+
+2. sysfs attributes structure
+
+RO read only value
+RW read/write value
+
+All thermal sysfs attributes will be represented under /sys/class/thermal
+/sys/class/thermal/
+
+Thermal zone device sys I/F, created once it's registered:
+|thermal_zone[0-*]:
+ |-----type: Type of the thermal zone
+ |-----temp: Current temperature
+ |-----mode: Working mode of the thermal zone
+ |-----trip_point_[0-*]_temp: Trip point temperature
+ |-----trip_point_[0-*]_type: Trip point type
+
+Thermal cooling device sys I/F, created once it's registered:
+|cooling_device[0-*]:
+ |-----type : Type of the cooling device(processor/fan/...)
+ |-----max_state: Maximum cooling state of the cooling device
+ |-----cur_state: Current cooling state of the cooling device
+
+
+These two dynamic attributes are created/removed in pairs.
+They represent the relationship between a thermal zone and its associated cooling device.
+They are created/removed for each
+thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful exection.
+
+|thermal_zone[0-*]
+ |-----cdev[0-*]: The [0-*]th cooling device in the current thermal zone
+ |-----cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
+
+
+***************************
+* Thermal zone attributes *
+***************************
+
+type Strings which represent the thermal zone type.
+ This is given by thermal zone driver as part of registration.
+ Eg: "ACPI thermal zone" indicates it's a ACPI thermal device
+ RO
+ Optional
+
+temp Current temperature as reported by thermal zone (sensor)
+ Unit: degree celsius
+ RO
+ Required
+
+mode One of the predifned values in [kernel, user]
+ This file gives information about the algorithm
+ that is currently managing the thermal zone.
+ It can be either default kernel based algorithm
+ or user space application.
+ RW
+ Optional
+ kernel = Thermal management in kernel thermal zone driver.
+ user = Preventing kernel thermal zone driver actions upon
+ trip points so that user application can take full
+ charge of the thermal management.
+
+trip_point_[0-*]_temp The temperature above which trip point will be fired
+ Unit: degree celsius
+ RO
+ Optional
+
+trip_point_[0-*]_type Strings which indicate the type of the trip point
+ Eg. it can be one of critical, hot, passive,
+ active[0-*] for ACPI thermal zone.
+ RO
+ Optional
+
+cdev[0-*] Sysfs link to the thermal cooling device node where the sys I/F
+ for cooling device throttling control represents.
+ RO
+ Optional
+
+cdev[0-*]_trip_point The trip point with which cdev[0-*] is assocated in this thermal zone
+ -1 means the cooling device is not associated with any trip point.
+ RO
+ Optional
+
+******************************
+* Cooling device attributes *
+******************************
+
+type String which represents the type of device
+ eg: For generic ACPI: this should be "Fan",
+ "Processor" or "LCD"
+ eg. For memory controller device on intel_menlow platform:
+ this should be "Memory controller"
+ RO
+ Optional
+
+max_state The maximum permissible cooling state of this cooling device.
+ RO
+ Required
+
+cur_state The current cooling state of this cooling device.
+ the value can any integer numbers between 0 and max_state,
+ cur_state == 0 means no cooling
+ cur_state == max_state means the maximum cooling.
+ RW
+ Required
+
+3. A simple implementation
+
+ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
+If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
+it may register itself as a thermale_zone_device (thermal_zone1) with 4 trip points in all.
+It has one processor and one fan, which are both registered as thermal_cooling_device.
+If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
+the sys I/F structure will be built like this:
+
+/sys/class/thermal:
+
+|thermal_zone1:
+ |-----type: ACPI thermal zone
+ |-----temp: 37
+ |-----mode: kernel
+ |-----trip_point_0_temp: 100
+ |-----trip_point_0_type: critical
+ |-----trip_point_1_temp: 80
+ |-----trip_point_1_type: passive
+ |-----trip_point_2_temp: 70
+ |-----trip_point_2_type: active[0]
+ |-----trip_point_3_temp: 60
+ |-----trip_point_3_type: active[1]
+ |-----cdev0: --->/sys/class/thermal/cooling_device0
+ |-----cdev0_trip_point: 1 /* cdev0 can be used for passive */
+ |-----cdev1: --->/sys/class/thermal/cooling_device3
+ |-----cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
+
+|cooling_device0:
+ |-----type: Processor
+ |-----max_state: 8
+ |-----cur_state: 0
+
+|cooling_device3:
+ |-----type: Fan
+ |-----max_state: 2
+ |-----cur_state: 0