498 lines
20 KiB
Plaintext
498 lines
20 KiB
Plaintext
Generic Thermal Sysfs driver How To
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===================================
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Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
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Updated: 2 January 2008
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Copyright (c) 2008 Intel Corporation
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0. Introduction
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The generic thermal sysfs provides a set of interfaces for thermal zone
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devices (sensors) and thermal cooling devices (fan, processor...) to register
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with the thermal management solution and to be a part of it.
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This how-to focuses on enabling new thermal zone and cooling devices to
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participate in thermal management.
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This solution is platform independent and any type of thermal zone devices
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and cooling devices should be able to make use of the infrastructure.
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The main task of the thermal sysfs driver is to expose thermal zone attributes
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as well as cooling device attributes to the user space.
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An intelligent thermal management application can make decisions based on
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inputs from thermal zone attributes (the current temperature and trip point
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temperature) and throttle appropriate devices.
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[0-*] denotes any positive number starting from 0
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[1-*] denotes any positive number starting from 1
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1. thermal sysfs driver interface functions
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1.1 thermal zone device interface
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1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *type,
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int trips, int mask, void *devdata,
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struct thermal_zone_device_ops *ops,
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const struct thermal_zone_params *tzp,
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int passive_delay, int polling_delay))
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This interface function adds a new thermal zone device (sensor) to
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/sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
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thermal cooling devices registered at the same time.
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type: the thermal zone type.
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trips: the total number of trip points this thermal zone supports.
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mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
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devdata: device private data
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ops: thermal zone device call-backs.
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.bind: bind the thermal zone device with a thermal cooling device.
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.unbind: unbind the thermal zone device with a thermal cooling device.
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.get_temp: get the current temperature of the thermal zone.
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.get_mode: get the current mode (enabled/disabled) of the thermal zone.
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- "enabled" means the kernel thermal management is enabled.
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- "disabled" will prevent kernel thermal driver action upon trip points
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so that user applications can take charge of thermal management.
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.set_mode: set the mode (enabled/disabled) of the thermal zone.
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.get_trip_type: get the type of certain trip point.
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.get_trip_temp: get the temperature above which the certain trip point
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will be fired.
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.set_emul_temp: set the emulation temperature which helps in debugging
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different threshold temperature points.
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tzp: thermal zone platform parameters.
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passive_delay: number of milliseconds to wait between polls when
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performing passive cooling.
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polling_delay: number of milliseconds to wait between polls when checking
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whether trip points have been crossed (0 for interrupt driven systems).
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1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
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This interface function removes the thermal zone device.
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It deletes the corresponding entry form /sys/class/thermal folder and
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unbind all the thermal cooling devices it uses.
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1.2 thermal cooling device interface
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1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
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void *devdata, struct thermal_cooling_device_ops *)
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This interface function adds a new thermal cooling device (fan/processor/...)
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to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
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to all the thermal zone devices register at the same time.
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name: the cooling device name.
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devdata: device private data.
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ops: thermal cooling devices call-backs.
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.get_max_state: get the Maximum throttle state of the cooling device.
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.get_cur_state: get the Current throttle state of the cooling device.
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.set_cur_state: set the Current throttle state of the cooling device.
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1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
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This interface function remove the thermal cooling device.
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It deletes the corresponding entry form /sys/class/thermal folder and
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unbind itself from all the thermal zone devices using it.
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1.3 interface for binding a thermal zone device with a thermal cooling device
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1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
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int trip, struct thermal_cooling_device *cdev,
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unsigned long upper, unsigned long lower, unsigned int weight);
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This interface function bind a thermal cooling device to the certain trip
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point of a thermal zone device.
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This function is usually called in the thermal zone device .bind callback.
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tz: the thermal zone device
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cdev: thermal cooling device
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trip: indicates which trip point the cooling devices is associated with
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in this thermal zone.
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upper:the Maximum cooling state for this trip point.
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THERMAL_NO_LIMIT means no upper limit,
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and the cooling device can be in max_state.
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lower:the Minimum cooling state can be used for this trip point.
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THERMAL_NO_LIMIT means no lower limit,
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and the cooling device can be in cooling state 0.
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weight: the influence of this cooling device in this thermal
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zone. See 1.4.1 below for more information.
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1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
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int trip, struct thermal_cooling_device *cdev);
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This interface function unbind a thermal cooling device from the certain
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trip point of a thermal zone device. This function is usually called in
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the thermal zone device .unbind callback.
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tz: the thermal zone device
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cdev: thermal cooling device
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trip: indicates which trip point the cooling devices is associated with
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in this thermal zone.
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1.4 Thermal Zone Parameters
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1.4.1 struct thermal_bind_params
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This structure defines the following parameters that are used to bind
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a zone with a cooling device for a particular trip point.
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.cdev: The cooling device pointer
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.weight: The 'influence' of a particular cooling device on this
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zone. This is relative to the rest of the cooling
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devices. For example, if all cooling devices have a
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weight of 1, then they all contribute the same. You can
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use percentages if you want, but it's not mandatory. A
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weight of 0 means that this cooling device doesn't
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contribute to the cooling of this zone unless all cooling
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devices have a weight of 0. If all weights are 0, then
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they all contribute the same.
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.trip_mask:This is a bit mask that gives the binding relation between
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this thermal zone and cdev, for a particular trip point.
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If nth bit is set, then the cdev and thermal zone are bound
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for trip point n.
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.limits: This is an array of cooling state limits. Must have exactly
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2 * thermal_zone.number_of_trip_points. It is an array consisting
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of tuples <lower-state upper-state> of state limits. Each trip
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will be associated with one state limit tuple when binding.
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A NULL pointer means <THERMAL_NO_LIMITS THERMAL_NO_LIMITS>
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on all trips. These limits are used when binding a cdev to a
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trip point.
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.match: This call back returns success(0) if the 'tz and cdev' need to
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be bound, as per platform data.
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1.4.2 struct thermal_zone_params
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This structure defines the platform level parameters for a thermal zone.
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This data, for each thermal zone should come from the platform layer.
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This is an optional feature where some platforms can choose not to
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provide this data.
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.governor_name: Name of the thermal governor used for this zone
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.no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
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is required. when no_hwmon == false, a hwmon sysfs interface
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will be created. when no_hwmon == true, nothing will be done.
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In case the thermal_zone_params is NULL, the hwmon interface
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will be created (for backward compatibility).
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.num_tbps: Number of thermal_bind_params entries for this zone
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.tbp: thermal_bind_params entries
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2. sysfs attributes structure
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RO read only value
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RW read/write value
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Thermal sysfs attributes will be represented under /sys/class/thermal.
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Hwmon sysfs I/F extension is also available under /sys/class/hwmon
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if hwmon is compiled in or built as a module.
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Thermal zone device sys I/F, created once it's registered:
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/sys/class/thermal/thermal_zone[0-*]:
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|---type: Type of the thermal zone
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|---temp: Current temperature
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|---mode: Working mode of the thermal zone
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|---policy: Thermal governor used for this zone
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|---available_policies: Available thermal governors for this zone
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|---trip_point_[0-*]_temp: Trip point temperature
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|---trip_point_[0-*]_type: Trip point type
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|---trip_point_[0-*]_hyst: Hysteresis value for this trip point
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|---emul_temp: Emulated temperature set node
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|---sustainable_power: Sustainable dissipatable power
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|---k_po: Proportional term during temperature overshoot
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|---k_pu: Proportional term during temperature undershoot
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|---k_i: PID's integral term in the power allocator gov
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|---k_d: PID's derivative term in the power allocator
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|---integral_cutoff: Offset above which errors are accumulated
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|---slope: Slope constant applied as linear extrapolation
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|---offset: Offset constant applied as linear extrapolation
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Thermal cooling device sys I/F, created once it's registered:
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/sys/class/thermal/cooling_device[0-*]:
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|---type: Type of the cooling device(processor/fan/...)
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|---max_state: Maximum cooling state of the cooling device
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|---cur_state: Current cooling state of the cooling device
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Then next two dynamic attributes are created/removed in pairs. They represent
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the relationship between a thermal zone and its associated cooling device.
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They are created/removed for each successful execution of
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thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
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/sys/class/thermal/thermal_zone[0-*]:
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|---cdev[0-*]: [0-*]th cooling device in current thermal zone
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|---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
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|---cdev[0-*]_weight: Influence of the cooling device in
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this thermal zone
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Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
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the generic thermal driver also creates a hwmon sysfs I/F for each _type_
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of thermal zone device. E.g. the generic thermal driver registers one hwmon
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class device and build the associated hwmon sysfs I/F for all the registered
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ACPI thermal zones.
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/sys/class/hwmon/hwmon[0-*]:
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|---name: The type of the thermal zone devices
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|---temp[1-*]_input: The current temperature of thermal zone [1-*]
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|---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
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Please read Documentation/hwmon/sysfs-interface for additional information.
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***************************
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* Thermal zone attributes *
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***************************
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type
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Strings which represent the thermal zone type.
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This is given by thermal zone driver as part of registration.
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E.g: "acpitz" indicates it's an ACPI thermal device.
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In order to keep it consistent with hwmon sys attribute; this should
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be a short, lowercase string, not containing spaces nor dashes.
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RO, Required
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temp
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Current temperature as reported by thermal zone (sensor).
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Unit: millidegree Celsius
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RO, Required
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mode
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One of the predefined values in [enabled, disabled].
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This file gives information about the algorithm that is currently
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managing the thermal zone. It can be either default kernel based
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algorithm or user space application.
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enabled = enable Kernel Thermal management.
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disabled = Preventing kernel thermal zone driver actions upon
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trip points so that user application can take full
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charge of the thermal management.
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RW, Optional
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policy
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One of the various thermal governors used for a particular zone.
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RW, Required
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available_policies
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Available thermal governors which can be used for a particular zone.
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RO, Required
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trip_point_[0-*]_temp
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The temperature above which trip point will be fired.
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Unit: millidegree Celsius
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RO, Optional
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trip_point_[0-*]_type
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Strings which indicate the type of the trip point.
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E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
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thermal zone.
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RO, Optional
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trip_point_[0-*]_hyst
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The hysteresis value for a trip point, represented as an integer
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Unit: Celsius
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RW, Optional
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cdev[0-*]
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Sysfs link to the thermal cooling device node where the sys I/F
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for cooling device throttling control represents.
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RO, Optional
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cdev[0-*]_trip_point
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The trip point with which cdev[0-*] is associated in this thermal
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zone; -1 means the cooling device is not associated with any trip
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point.
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RO, Optional
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cdev[0-*]_weight
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The influence of cdev[0-*] in this thermal zone. This value
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is relative to the rest of cooling devices in the thermal
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zone. For example, if a cooling device has a weight double
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than that of other, it's twice as effective in cooling the
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thermal zone.
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RW, Optional
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passive
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Attribute is only present for zones in which the passive cooling
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policy is not supported by native thermal driver. Default is zero
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and can be set to a temperature (in millidegrees) to enable a
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passive trip point for the zone. Activation is done by polling with
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an interval of 1 second.
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Unit: millidegrees Celsius
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Valid values: 0 (disabled) or greater than 1000
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RW, Optional
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emul_temp
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Interface to set the emulated temperature method in thermal zone
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(sensor). After setting this temperature, the thermal zone may pass
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this temperature to platform emulation function if registered or
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cache it locally. This is useful in debugging different temperature
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threshold and its associated cooling action. This is write only node
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and writing 0 on this node should disable emulation.
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Unit: millidegree Celsius
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WO, Optional
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WARNING: Be careful while enabling this option on production systems,
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because userland can easily disable the thermal policy by simply
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flooding this sysfs node with low temperature values.
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sustainable_power
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An estimate of the sustained power that can be dissipated by
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the thermal zone. Used by the power allocator governor. For
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more information see Documentation/thermal/power_allocator.txt
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Unit: milliwatts
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RW, Optional
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k_po
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The proportional term of the power allocator governor's PID
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controller during temperature overshoot. Temperature overshoot
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is when the current temperature is above the "desired
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temperature" trip point. For more information see
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Documentation/thermal/power_allocator.txt
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RW, Optional
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k_pu
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The proportional term of the power allocator governor's PID
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controller during temperature undershoot. Temperature undershoot
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is when the current temperature is below the "desired
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temperature" trip point. For more information see
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Documentation/thermal/power_allocator.txt
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RW, Optional
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k_i
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The integral term of the power allocator governor's PID
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controller. This term allows the PID controller to compensate
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for long term drift. For more information see
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Documentation/thermal/power_allocator.txt
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RW, Optional
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k_d
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The derivative term of the power allocator governor's PID
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controller. For more information see
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Documentation/thermal/power_allocator.txt
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RW, Optional
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integral_cutoff
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Temperature offset from the desired temperature trip point
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above which the integral term of the power allocator
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governor's PID controller starts accumulating errors. For
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example, if integral_cutoff is 0, then the integral term only
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accumulates error when temperature is above the desired
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temperature trip point. For more information see
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Documentation/thermal/power_allocator.txt
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Unit: millidegree Celsius
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RW, Optional
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slope
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The slope constant used in a linear extrapolation model
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to determine a hotspot temperature based off the sensor's
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raw readings. It is up to the device driver to determine
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the usage of these values.
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RW, Optional
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offset
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The offset constant used in a linear extrapolation model
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to determine a hotspot temperature based off the sensor's
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raw readings. It is up to the device driver to determine
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the usage of these values.
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RW, Optional
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*****************************
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* Cooling device attributes *
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*****************************
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type
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String which represents the type of device, e.g:
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- for generic ACPI: should be "Fan", "Processor" or "LCD"
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- for memory controller device on intel_menlow platform:
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should be "Memory controller".
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RO, Required
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max_state
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The maximum permissible cooling state of this cooling device.
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RO, Required
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cur_state
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The current cooling state of this cooling device.
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The value can any integer numbers between 0 and max_state:
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- cur_state == 0 means no cooling
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- cur_state == max_state means the maximum cooling.
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RW, Required
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3. A simple implementation
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ACPI thermal zone may support multiple trip points like critical, hot,
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passive, active. If an ACPI thermal zone supports critical, passive,
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active[0] and active[1] at the same time, it may register itself as a
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thermal_zone_device (thermal_zone1) with 4 trip points in all.
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It has one processor and one fan, which are both registered as
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thermal_cooling_device. Both are considered to have the same
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effectiveness in cooling the thermal zone.
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If the processor is listed in _PSL method, and the fan is listed in _AL0
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method, the sys I/F structure will be built like this:
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/sys/class/thermal:
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|thermal_zone1:
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|---type: acpitz
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|---temp: 37000
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|---mode: enabled
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|---policy: step_wise
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|---available_policies: step_wise fair_share
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|---trip_point_0_temp: 100000
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|---trip_point_0_type: critical
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|---trip_point_1_temp: 80000
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|---trip_point_1_type: passive
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|---trip_point_2_temp: 70000
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|---trip_point_2_type: active0
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|---trip_point_3_temp: 60000
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|---trip_point_3_type: active1
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|---cdev0: --->/sys/class/thermal/cooling_device0
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|---cdev0_trip_point: 1 /* cdev0 can be used for passive */
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|---cdev0_weight: 1024
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|---cdev1: --->/sys/class/thermal/cooling_device3
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|---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
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|---cdev1_weight: 1024
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|cooling_device0:
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|---type: Processor
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|---max_state: 8
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|---cur_state: 0
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|cooling_device3:
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|---type: Fan
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|---max_state: 2
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|---cur_state: 0
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/sys/class/hwmon:
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|hwmon0:
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|---name: acpitz
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|---temp1_input: 37000
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|---temp1_crit: 100000
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4. Event Notification
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The framework includes a simple notification mechanism, in the form of a
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netlink event. Netlink socket initialization is done during the _init_
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of the framework. Drivers which intend to use the notification mechanism
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just need to call thermal_generate_netlink_event() with two arguments viz
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(originator, event). The originator is a pointer to struct thermal_zone_device
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from where the event has been originated. An integer which represents the
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thermal zone device will be used in the message to identify the zone. The
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event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
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THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
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crosses any of the configured thresholds.
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5. Export Symbol APIs:
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5.1: get_tz_trend:
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This function returns the trend of a thermal zone, i.e the rate of change
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of temperature of the thermal zone. Ideally, the thermal sensor drivers
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are supposed to implement the callback. If they don't, the thermal
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framework calculated the trend by comparing the previous and the current
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temperature values.
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5.2:get_thermal_instance:
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This function returns the thermal_instance corresponding to a given
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{thermal_zone, cooling_device, trip_point} combination. Returns NULL
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if such an instance does not exist.
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5.3:thermal_notify_framework:
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This function handles the trip events from sensor drivers. It starts
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throttling the cooling devices according to the policy configured.
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For CRITICAL and HOT trip points, this notifies the respective drivers,
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and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
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The throttling policy is based on the configured platform data; if no
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platform data is provided, this uses the step_wise throttling policy.
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5.4:thermal_cdev_update:
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This function serves as an arbitrator to set the state of a cooling
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device. It sets the cooling device to the deepest cooling state if
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possible.
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