496 lines
17 KiB
ReStructuredText
496 lines
17 KiB
ReStructuredText
===================================
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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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===============
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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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===========================================
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1.1 thermal zone device interface
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---------------------------------
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::
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struct thermal_zone_device
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*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:
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the thermal zone type.
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trips:
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the total number of trip points this thermal zone supports.
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mask:
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Bit string: If 'n'th bit is set, then trip point 'n' is writable.
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devdata:
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device private data
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ops:
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thermal zone device call-backs.
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.bind:
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bind the thermal zone device with a thermal cooling device.
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.unbind:
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unbind the thermal zone device with a thermal cooling device.
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.get_temp:
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get the current temperature of the thermal zone.
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.set_trips:
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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:
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get the current mode (enabled/disabled) of the thermal zone.
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- "enabled" means the kernel thermal management is
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enabled.
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- "disabled" will prevent kernel thermal driver action
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upon trip points so that user applications can take
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charge of thermal management.
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.set_mode:
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set the mode (enabled/disabled) of the thermal zone.
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.get_trip_type:
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get the type of certain trip point.
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.get_trip_temp:
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get the temperature above which the certain trip point
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will be fired.
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.set_emul_temp:
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set the emulation temperature which helps in debugging
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different threshold temperature points.
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tzp:
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thermal zone platform parameters.
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passive_delay:
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number of milliseconds to wait between polls when
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performing passive cooling.
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polling_delay:
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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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::
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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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::
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struct thermal_zone_device
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*thermal_zone_of_sensor_register(struct device *dev, int sensor_id,
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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:
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Device node of sensor containing valid node pointer in
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dev->of_node.
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sensor_id:
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a sensor identifier, in case the sensor IP has more
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than one sensors
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data:
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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:
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`struct thermal_zone_of_device_ops *`.
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============== =======================================
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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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============== =======================================
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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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::
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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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::
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struct thermal_zone_device
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*devm_thermal_zone_of_sensor_register(struct device *dev,
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int sensor_id,
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void *data,
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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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::
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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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::
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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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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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------------------------------------
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::
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struct thermal_cooling_device
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*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:
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the cooling device name.
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devdata:
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device private data.
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ops:
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thermal cooling devices call-backs.
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.get_max_state:
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get the Maximum throttle state of the cooling device.
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.get_cur_state:
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get the Currently requested throttle state of the
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cooling device.
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.set_cur_state:
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set the Current throttle state of the cooling device.
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::
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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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-----------------------------------------------------------------------------
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::
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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:
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the thermal zone device
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cdev:
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thermal cooling device
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trip:
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indicates which trip point in this thermal zone the cooling device
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is associated with.
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upper:
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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:
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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:
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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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::
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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:
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the thermal zone device
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cdev:
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thermal cooling device
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trip:
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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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---------------------------
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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:
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Name of the thermal governor used for this zone
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.no_hwmon:
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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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2. sysfs attributes structure
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=============================
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== ================
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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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== ================
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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: Cooling 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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::
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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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Please read Documentation/ABI/testing/sysfs-class-thermal for thermal
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zone and cooling device attribute details.
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::
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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.rst for additional information.
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3. A simple implementation
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==========================
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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. Export Symbol APIs
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=====================
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4.1. get_tz_trend
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-----------------
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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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4.2. get_thermal_instance
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-------------------------
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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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4.3. thermal_cdev_update
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------------------------
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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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5. thermal_emergency_poweroff
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=============================
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On an event of critical trip temperature crossing the thermal framework
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shuts down the system by calling hw_protection_shutdown(). The
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hw_protection_shutdown() first attempts to perform an orderly shutdown
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but accepts a delay after which it proceeds doing a forced power-off
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or as last resort an emergency_restart.
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The delay should be carefully profiled so as to give adequate time for
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orderly poweroff.
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If the delay is set to 0 emergency poweroff will not be supported. So a
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carefully profiled non-zero positive value is a must for emergency
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poweroff to be triggered.
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