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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 focuses 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 *type,
+		int trips, int mask, void *devdata,
+		struct thermal_zone_device_ops *ops,
+		const struct thermal_zone_params *tzp,
+		int passive_delay, int polling_delay))
+
+    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.
+
+    type: the thermal zone type.
+    trips: the total number of trip points this thermal zone supports.
+    mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
+    devdata: device private data
+    ops: thermal zone device call-backs.
+	.bind: bind the thermal zone device with a thermal cooling device.
+	.unbind: unbind 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 (enabled/disabled) of the thermal zone.
+	    - "enabled" means the kernel thermal management is enabled.
+	    - "disabled" will prevent kernel thermal driver action upon trip points
+	      so that user applications can take charge of thermal management.
+	.set_mode: set the mode (enabled/disabled) 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.
+	.set_emul_temp: set the emulation temperature which helps in debugging
+			different threshold temperature points.
+    tzp: thermal zone platform parameters.
+    passive_delay: number of milliseconds to wait between polls when
+	performing passive cooling.
+    polling_delay: number of milliseconds to wait between polls when checking
+	whether trip points have been crossed (0 for interrupt driven systems).
+
+
+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 call-backs.
+	.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,
+	unsigned long upper, unsigned long lower);
+
+    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.
+    upper:the Maximum cooling state for this trip point.
+          THERMAL_NO_LIMIT means no upper limit,
+	  and the cooling device can be in max_state.
+    lower:the Minimum cooling state can be used for this trip point.
+          THERMAL_NO_LIMIT means no lower limit,
+	  and the cooling device can be in cooling state 0.
+
+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.
+
+1.4 Thermal Zone Parameters
+1.4.1 struct thermal_bind_params
+    This structure defines the following parameters that are used to bind
+    a zone with a cooling device for a particular trip point.
+    .cdev: The cooling device pointer
+    .weight: The 'influence' of a particular cooling device on this zone.
+             This is on a percentage scale. The sum of all these weights
+             (for a particular zone) cannot exceed 100.
+    .trip_mask:This is a bit mask that gives the binding relation between
+               this thermal zone and cdev, for a particular trip point.
+               If nth bit is set, then the cdev and thermal zone are bound
+               for trip point n.
+    .limits: This is an array of cooling state limits. Must have exactly
+         2 * thermal_zone.number_of_trip_points. It is an array consisting
+         of tuples <lower-state upper-state> of state limits. Each trip
+         will be associated with one state limit tuple when binding.
+         A NULL pointer means <THERMAL_NO_LIMITS THERMAL_NO_LIMITS>
+         on all trips. These limits are used when binding a cdev to a
+         trip point.
+    .match: This call back returns success(0) if the 'tz and cdev' need to
+	    be bound, as per platform data.
+1.4.2 struct thermal_zone_params
+    This structure defines the platform level parameters for a thermal zone.
+    This data, for each thermal zone should come from the platform layer.
+    This is an optional feature where some platforms can choose not to
+    provide this data.
+    .governor_name: Name of the thermal governor used for this zone
+    .no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
+               is required. when no_hwmon == false, a hwmon sysfs interface
+               will be created. when no_hwmon == true, nothing will be done.
+               In case the thermal_zone_params is NULL, the hwmon interface
+               will be created (for backward compatibility).
+    .num_tbps: Number of thermal_bind_params entries for this zone
+    .tbp: thermal_bind_params entries
+
+2. sysfs attributes structure
+
+RO	read only value
+RW	read/write value
+
+Thermal sysfs attributes will be represented under /sys/class/thermal.
+Hwmon sysfs I/F extension is also available under /sys/class/hwmon
+if hwmon is compiled in or built as a module.
+
+Thermal zone device sys I/F, created once it's registered:
+/sys/class/thermal/thermal_zone[0-*]:
+    |---type:			Type of the thermal zone
+    |---temp:			Current temperature
+    |---mode:			Working mode of the thermal zone
+    |---policy:			Thermal governor used for this zone
+    |---trip_point_[0-*]_temp:	Trip point temperature
+    |---trip_point_[0-*]_type:	Trip point type
+    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point
+    |---emul_temp:		Emulated temperature set node
+
+Thermal cooling device sys I/F, created once it's registered:
+/sys/class/thermal/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
+
+
+Then next 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 successful execution of
+thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
+
+/sys/class/thermal/thermal_zone[0-*]:
+    |---cdev[0-*]:		[0-*]th cooling device in current thermal zone
+    |---cdev[0-*]_trip_point:	Trip point that cdev[0-*] is associated with
+
+Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
+the generic thermal driver also creates a hwmon sysfs I/F for each _type_
+of thermal zone device. E.g. the generic thermal driver registers one hwmon
+class device and build the associated hwmon sysfs I/F for all the registered
+ACPI thermal zones.
+
+/sys/class/hwmon/hwmon[0-*]:
+    |---name:			The type of the thermal zone devices
+    |---temp[1-*]_input:	The current temperature of thermal zone [1-*]
+    |---temp[1-*]_critical:	The critical trip point of thermal zone [1-*]
+
+Please read Documentation/hwmon/sysfs-interface for additional information.
+
+***************************
+* Thermal zone attributes *
+***************************
+
+type
+	Strings which represent the thermal zone type.
+	This is given by thermal zone driver as part of registration.
+	E.g: "acpitz" indicates it's an ACPI thermal device.
+	In order to keep it consistent with hwmon sys attribute; this should
+	be a short, lowercase string, not containing spaces nor dashes.
+	RO, Required
+
+temp
+	Current temperature as reported by thermal zone (sensor).
+	Unit: millidegree Celsius
+	RO, Required
+
+mode
+	One of the predefined values in [enabled, disabled].
+	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.
+	enabled		= enable Kernel Thermal management.
+	disabled	= Preventing kernel thermal zone driver actions upon
+			  trip points so that user application can take full
+			  charge of the thermal management.
+	RW, Optional
+
+policy
+	One of the various thermal governors used for a particular zone.
+	RW, Required
+
+trip_point_[0-*]_temp
+	The temperature above which trip point will be fired.
+	Unit: millidegree Celsius
+	RO, Optional
+
+trip_point_[0-*]_type
+	Strings which indicate the type of the trip point.
+	E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
+	thermal zone.
+	RO, Optional
+
+trip_point_[0-*]_hyst
+	The hysteresis value for a trip point, represented as an integer
+	Unit: Celsius
+	RW, 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 associated in this thermal
+	zone; -1 means the cooling device is not associated with any trip
+	point.
+	RO, Optional
+
+passive
+	Attribute is only present for zones in which the passive cooling
+	policy is not supported by native thermal driver. Default is zero
+	and can be set to a temperature (in millidegrees) to enable a
+	passive trip point for the zone. Activation is done by polling with
+	an interval of 1 second.
+	Unit: millidegrees Celsius
+	Valid values: 0 (disabled) or greater than 1000
+	RW, Optional
+
+emul_temp
+	Interface to set the emulated temperature method in thermal zone
+	(sensor). After setting this temperature, the thermal zone may pass
+	this temperature to platform emulation function if registered or
+	cache it locally. This is useful in debugging different temperature
+	threshold and its associated cooling action. This is write only node
+	and writing 0 on this node should disable emulation.
+	Unit: millidegree Celsius
+	WO, Optional
+
+	  WARNING: Be careful while enabling this option on production systems,
+	  because userland can easily disable the thermal policy by simply
+	  flooding this sysfs node with low temperature values.
+
+*****************************
+* Cooling device attributes *
+*****************************
+
+type
+	String which represents the type of device, e.g:
+	- for generic ACPI: should be "Fan", "Processor" or "LCD"
+	- for memory controller device on intel_menlow platform:
+	  should be "Memory controller".
+	RO, Required
+
+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
+thermal_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:			acpitz
+    |---temp:			37000
+    |---mode:			enabled
+    |---policy:			step_wise
+    |---trip_point_0_temp:	100000
+    |---trip_point_0_type:	critical
+    |---trip_point_1_temp:	80000
+    |---trip_point_1_type:	passive
+    |---trip_point_2_temp:	70000
+    |---trip_point_2_type:	active0
+    |---trip_point_3_temp:	60000
+    |---trip_point_3_type:	active1
+    |---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
+
+/sys/class/hwmon:
+
+|hwmon0:
+    |---name:			acpitz
+    |---temp1_input:		37000
+    |---temp1_crit:		100000
+
+4. Event Notification
+
+The framework includes a simple notification mechanism, in the form of a
+netlink event. Netlink socket initialization is done during the _init_
+of the framework. Drivers which intend to use the notification mechanism
+just need to call thermal_generate_netlink_event() with two arguments viz
+(originator, event). The originator is a pointer to struct thermal_zone_device
+from where the event has been originated. An integer which represents the
+thermal zone device will be used in the message to identify the zone. The
+event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
+THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
+crosses any of the configured thresholds.
+
+5. Export Symbol APIs:
+
+5.1: get_tz_trend:
+This function returns the trend of a thermal zone, i.e the rate of change
+of temperature of the thermal zone. Ideally, the thermal sensor drivers
+are supposed to implement the callback. If they don't, the thermal
+framework calculated the trend by comparing the previous and the current
+temperature values.
+
+5.2:get_thermal_instance:
+This function returns the thermal_instance corresponding to a given
+{thermal_zone, cooling_device, trip_point} combination. Returns NULL
+if such an instance does not exist.
+
+5.3:thermal_notify_framework:
+This function handles the trip events from sensor drivers. It starts
+throttling the cooling devices according to the policy configured.
+For CRITICAL and HOT trip points, this notifies the respective drivers,
+and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
+The throttling policy is based on the configured platform data; if no
+platform data is provided, this uses the step_wise throttling policy.
+
+5.4:thermal_cdev_update:
+This function serves as an arbitrator to set the state of a cooling
+device. It sets the cooling device to the deepest cooling state if
+possible.