8ea229511e
This extends the sysfs interface for thermal cooling devices and exposes some pretty useful statistics. These statistics have proven to be quite useful specially while doing benchmarks related to the task scheduler, where we want to make sure that nothing has disrupted the test, specially the cooling device which may have put constraints on the CPUs. The information exposed here tells us to what extent the CPUs were constrained by the thermal framework. The write-only "reset" file is used to reset the statistics. The read-only "time_in_state_ms" file shows the time (in msec) spent by the device in the respective cooling states, and it prints one line per cooling state. The read-only "total_trans" file shows single positive integer value showing the total number of cooling state transitions the device has gone through since the time the cooling device is registered or the time when statistics were reset last. The read-only "trans_table" file shows a two dimensional matrix, where an entry <i,j> (row i, column j) represents the number of transitions from State_i to State_j. This is how the directory structure looks like for a single cooling device: $ ls -R /sys/class/thermal/cooling_device0/ /sys/class/thermal/cooling_device0/: cur_state max_state power stats subsystem type uevent /sys/class/thermal/cooling_device0/power: autosuspend_delay_ms runtime_active_time runtime_suspended_time control runtime_status /sys/class/thermal/cooling_device0/stats: reset time_in_state_ms total_trans trans_table This is tested on ARM 64-bit Hisilicon hikey620 board running Ubuntu and ARM 64-bit Hisilicon hikey960 board running Android. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
636 lines
26 KiB
Text
636 lines
26 KiB
Text
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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.set_trips: set the trip points window. Whenever the current temperature
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is updated, the trip points immediately below and above the
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current temperature are found.
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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 from /sys/class/thermal folder and
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unbinds all the thermal cooling devices it uses.
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1.1.3 struct thermal_zone_device *thermal_zone_of_sensor_register(
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struct device *dev, int sensor_id, void *data,
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const struct thermal_zone_of_device_ops *ops)
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This interface adds a new sensor to a DT thermal zone.
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This function will search the list of thermal zones described in
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device tree and look for the zone that refer to the sensor device
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pointed by dev->of_node as temperature providers. For the zone
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pointing to the sensor node, the sensor will be added to the DT
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thermal zone device.
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The parameters for this interface are:
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dev: Device node of sensor containing valid node pointer in
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dev->of_node.
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sensor_id: a sensor identifier, in case the sensor IP has more
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than one sensors
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data: a private pointer (owned by the caller) that will be
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passed back, when a temperature reading is needed.
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ops: struct thermal_zone_of_device_ops *.
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get_temp: a pointer to a function that reads the
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sensor temperature. This is mandatory
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callback provided by sensor driver.
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set_trips: a pointer to a function that sets a
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temperature window. When this window is
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left the driver must inform the thermal
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core via thermal_zone_device_update.
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get_trend: a pointer to a function that reads the
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sensor temperature trend.
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set_emul_temp: a pointer to a function that sets
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sensor emulated temperature.
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The thermal zone temperature is provided by the get_temp() function
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pointer of thermal_zone_of_device_ops. When called, it will
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have the private pointer @data back.
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It returns error pointer if fails otherwise valid thermal zone device
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handle. Caller should check the return handle with IS_ERR() for finding
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whether success or not.
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1.1.4 void thermal_zone_of_sensor_unregister(struct device *dev,
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struct thermal_zone_device *tzd)
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This interface unregisters a sensor from a DT thermal zone which was
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successfully added by interface thermal_zone_of_sensor_register().
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This function removes the sensor callbacks and private data from the
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thermal zone device registered with thermal_zone_of_sensor_register()
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interface. It will also silent the zone by remove the .get_temp() and
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get_trend() thermal zone device callbacks.
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1.1.5 struct thermal_zone_device *devm_thermal_zone_of_sensor_register(
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struct device *dev, int sensor_id,
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void *data, const struct thermal_zone_of_device_ops *ops)
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This interface is resource managed version of
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thermal_zone_of_sensor_register().
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All details of thermal_zone_of_sensor_register() described in
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section 1.1.3 is applicable here.
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The benefit of using this interface to register sensor is that it
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is not require to explicitly call thermal_zone_of_sensor_unregister()
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in error path or during driver unbinding as this is done by driver
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resource manager.
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1.1.6 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
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struct thermal_zone_device *tzd)
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This interface is resource managed version of
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thermal_zone_of_sensor_unregister().
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All details of thermal_zone_of_sensor_unregister() described in
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section 1.1.4 is applicable here.
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Normally this function will not need to be called and the resource
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management code will ensure that the resource is freed.
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1.1.7 int thermal_zone_get_slope(struct thermal_zone_device *tz)
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This interface is used to read the slope attribute value
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for the thermal zone device, which might be useful for platform
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drivers for temperature calculations.
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1.1.8 int thermal_zone_get_offset(struct thermal_zone_device *tz)
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This interface is used to read the offset attribute value
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for the thermal zone device, which might be useful for platform
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drivers for temperature calculations.
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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 registered 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 Currently requested 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 removes the thermal cooling device.
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It deletes the corresponding entry from /sys/class/thermal folder and
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unbinds 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 binds a thermal cooling device to a particular 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 in this thermal zone the cooling device
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is associated with.
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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 unbinds a thermal cooling device from a particular
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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 in this thermal zone the cooling device
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is associated with.
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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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.binding_limits: This is an array of cooling state limits. Must have
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exactly 2 * thermal_zone.number_of_trip_points. It is an
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array consisting of tuples <lower-state upper-state> of
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state limits. Each trip will be associated with one state
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limit tuple when binding. A NULL pointer means
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<THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips.
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These limits are used when binding a cdev to a 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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WO write 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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|---stats: Directory containing cooling device's statistics
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|---stats/reset: Writing any value resets the statistics
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|---stats/time_in_state_ms: Time (msec) spent in various cooling states
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|---stats/total_trans: Total number of times cooling state is changed
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|---stats/trans_table: Cooing state transition table
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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 in this thermal zone which cdev[0-*] is associated
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with; -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
|
|
Documentation/thermal/power_allocator.txt
|
|
RW, Optional
|
|
|
|
integral_cutoff
|
|
Temperature offset from the desired temperature trip point
|
|
above which the integral term of the power allocator
|
|
governor's PID controller starts accumulating errors. For
|
|
example, if integral_cutoff is 0, then the integral term only
|
|
accumulates error when temperature is above the desired
|
|
temperature trip point. For more information see
|
|
Documentation/thermal/power_allocator.txt
|
|
Unit: millidegree Celsius
|
|
RW, Optional
|
|
|
|
slope
|
|
The slope constant used in a linear extrapolation model
|
|
to determine a hotspot temperature based off the sensor's
|
|
raw readings. It is up to the device driver to determine
|
|
the usage of these values.
|
|
RW, Optional
|
|
|
|
offset
|
|
The offset constant used in a linear extrapolation model
|
|
to determine a hotspot temperature based off the sensor's
|
|
raw readings. It is up to the device driver to determine
|
|
the usage of these values.
|
|
RW, Optional
|
|
|
|
*****************************
|
|
* 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
|
|
|
|
stats/reset
|
|
Writing any value resets the cooling device's statistics.
|
|
WO, Required
|
|
|
|
stats/time_in_state_ms:
|
|
The amount of time spent by the cooling device in various cooling
|
|
states. The output will have "<state> <time>" pair in each line, which
|
|
will mean this cooling device spent <time> msec of time at <state>.
|
|
Output will have one line for each of the supported states. usertime
|
|
units here is 10mS (similar to other time exported in /proc).
|
|
RO, Required
|
|
|
|
stats/total_trans:
|
|
A single positive value showing the total number of times the state of a
|
|
cooling device is changed.
|
|
RO, Required
|
|
|
|
stats/trans_table:
|
|
This gives fine grained information about all the cooling state
|
|
transitions. The cat output here is a two dimensional matrix, where an
|
|
entry <i,j> (row i, column j) represents the number of transitions from
|
|
State_i to State_j. If the transition table is bigger than PAGE_SIZE,
|
|
reading this will return an -EFBIG error.
|
|
RO, 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. Both are considered to have the same
|
|
effectiveness in cooling the thermal zone.
|
|
|
|
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
|
|
|---available_policies: step_wise fair_share
|
|
|---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 */
|
|
|---cdev0_weight: 1024
|
|
|---cdev1: --->/sys/class/thermal/cooling_device3
|
|
|---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
|
|
|---cdev1_weight: 1024
|
|
|
|
|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.
|
|
|
|
6. thermal_emergency_poweroff:
|
|
|
|
On an event of critical trip temperature crossing. Thermal framework
|
|
allows the system to shutdown gracefully by calling orderly_poweroff().
|
|
In the event of a failure of orderly_poweroff() to shut down the system
|
|
we are in danger of keeping the system alive at undesirably high
|
|
temperatures. To mitigate this high risk scenario we program a work
|
|
queue to fire after a pre-determined number of seconds to start
|
|
an emergency shutdown of the device using the kernel_power_off()
|
|
function. In case kernel_power_off() fails then finally
|
|
emergency_restart() is called in the worst case.
|
|
|
|
The delay should be carefully profiled so as to give adequate time for
|
|
orderly_poweroff(). In case of failure of an orderly_poweroff() the
|
|
emergency poweroff kicks in after the delay has elapsed and shuts down
|
|
the system.
|
|
|
|
If set to 0 emergency poweroff will not be supported. So a carefully
|
|
profiled non-zero positive value is a must for emergerncy poweroff to be
|
|
triggered.
|