| =================================== |
| Generic Thermal Sysfs driver How To |
| =================================== |
| |
| Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com> |
| |
| Updated: 2 January 2008 |
| |
| Copyright (c) 2008 Intel Corporation |
| |
| |
| 0. Introduction |
| =============== |
| |
| The generic thermal sysfs provides a set of interfaces for thermal zone |
| devices (sensors) and thermal cooling devices (fan, processor...) to register |
| with the thermal management solution and to be a part of it. |
| |
| This how-to focuses on enabling new thermal zone and cooling devices to |
| participate in thermal management. |
| This solution is platform independent and any type of thermal zone devices |
| and cooling devices should be able to make use of the infrastructure. |
| |
| The main task of the thermal sysfs driver is to expose thermal zone attributes |
| as well as cooling device attributes to the user space. |
| An intelligent thermal management application can make decisions based on |
| inputs from thermal zone attributes (the current temperature and trip point |
| temperature) and throttle appropriate devices. |
| |
| - `[0-*]` denotes any positive number starting from 0 |
| - `[1-*]` denotes any positive number starting from 1 |
| |
| 1. thermal sysfs driver interface functions |
| =========================================== |
| |
| 1.1 thermal zone device interface |
| --------------------------------- |
| |
| :: |
| |
| struct thermal_zone_device |
| *thermal_zone_device_register(char *type, |
| int trips, int mask, void *devdata, |
| struct thermal_zone_device_ops *ops, |
| const struct thermal_zone_params *tzp, |
| int passive_delay, int polling_delay)) |
| |
| This interface function adds a new thermal zone device (sensor) to |
| /sys/class/thermal folder as `thermal_zone[0-*]`. It tries to bind all the |
| thermal cooling devices registered at the same time. |
| |
| type: |
| the thermal zone type. |
| trips: |
| the total number of trip points this thermal zone supports. |
| mask: |
| Bit string: If 'n'th bit is set, then trip point 'n' is writable. |
| devdata: |
| device private data |
| ops: |
| thermal zone device call-backs. |
| |
| .bind: |
| bind the thermal zone device with a thermal cooling device. |
| .unbind: |
| unbind the thermal zone device with a thermal cooling device. |
| .get_temp: |
| get the current temperature of the thermal zone. |
| .set_trips: |
| set the trip points window. Whenever the current temperature |
| is updated, the trip points immediately below and above the |
| current temperature are found. |
| .get_mode: |
| get the current mode (enabled/disabled) of the thermal zone. |
| |
| - "enabled" means the kernel thermal management is |
| enabled. |
| - "disabled" will prevent kernel thermal driver action |
| upon trip points so that user applications can take |
| charge of thermal management. |
| .set_mode: |
| set the mode (enabled/disabled) of the thermal zone. |
| .get_trip_type: |
| get the type of certain trip point. |
| .get_trip_temp: |
| get the temperature above which the certain trip point |
| will be fired. |
| .set_emul_temp: |
| set the emulation temperature which helps in debugging |
| different threshold temperature points. |
| tzp: |
| thermal zone platform parameters. |
| passive_delay: |
| number of milliseconds to wait between polls when |
| performing passive cooling. |
| polling_delay: |
| number of milliseconds to wait between polls when checking |
| whether trip points have been crossed (0 for interrupt driven systems). |
| |
| :: |
| |
| void thermal_zone_device_unregister(struct thermal_zone_device *tz) |
| |
| This interface function removes the thermal zone device. |
| It deletes the corresponding entry from /sys/class/thermal folder and |
| unbinds all the thermal cooling devices it uses. |
| |
| :: |
| |
| struct thermal_zone_device |
| *thermal_zone_of_sensor_register(struct device *dev, int sensor_id, |
| void *data, |
| const struct thermal_zone_of_device_ops *ops) |
| |
| This interface adds a new sensor to a DT thermal zone. |
| This function will search the list of thermal zones described in |
| device tree and look for the zone that refer to the sensor device |
| pointed by dev->of_node as temperature providers. For the zone |
| pointing to the sensor node, the sensor will be added to the DT |
| thermal zone device. |
| |
| The parameters for this interface are: |
| |
| dev: |
| Device node of sensor containing valid node pointer in |
| dev->of_node. |
| sensor_id: |
| a sensor identifier, in case the sensor IP has more |
| than one sensors |
| data: |
| a private pointer (owned by the caller) that will be |
| passed back, when a temperature reading is needed. |
| ops: |
| `struct thermal_zone_of_device_ops *`. |
| |
| ============== ======================================= |
| get_temp a pointer to a function that reads the |
| sensor temperature. This is mandatory |
| callback provided by sensor driver. |
| set_trips a pointer to a function that sets a |
| temperature window. When this window is |
| left the driver must inform the thermal |
| core via thermal_zone_device_update. |
| get_trend a pointer to a function that reads the |
| sensor temperature trend. |
| set_emul_temp a pointer to a function that sets |
| sensor emulated temperature. |
| ============== ======================================= |
| |
| The thermal zone temperature is provided by the get_temp() function |
| pointer of thermal_zone_of_device_ops. When called, it will |
| have the private pointer @data back. |
| |
| It returns error pointer if fails otherwise valid thermal zone device |
| handle. Caller should check the return handle with IS_ERR() for finding |
| whether success or not. |
| |
| :: |
| |
| void thermal_zone_of_sensor_unregister(struct device *dev, |
| struct thermal_zone_device *tzd) |
| |
| This interface unregisters a sensor from a DT thermal zone which was |
| successfully added by interface thermal_zone_of_sensor_register(). |
| This function removes the sensor callbacks and private data from the |
| thermal zone device registered with thermal_zone_of_sensor_register() |
| interface. It will also silent the zone by remove the .get_temp() and |
| get_trend() thermal zone device callbacks. |
| |
| :: |
| |
| struct thermal_zone_device |
| *devm_thermal_zone_of_sensor_register(struct device *dev, |
| int sensor_id, |
| void *data, |
| const struct thermal_zone_of_device_ops *ops) |
| |
| This interface is resource managed version of |
| thermal_zone_of_sensor_register(). |
| |
| All details of thermal_zone_of_sensor_register() described in |
| section 1.1.3 is applicable here. |
| |
| The benefit of using this interface to register sensor is that it |
| is not require to explicitly call thermal_zone_of_sensor_unregister() |
| in error path or during driver unbinding as this is done by driver |
| resource manager. |
| |
| :: |
| |
| void devm_thermal_zone_of_sensor_unregister(struct device *dev, |
| struct thermal_zone_device *tzd) |
| |
| This interface is resource managed version of |
| thermal_zone_of_sensor_unregister(). |
| All details of thermal_zone_of_sensor_unregister() described in |
| section 1.1.4 is applicable here. |
| Normally this function will not need to be called and the resource |
| management code will ensure that the resource is freed. |
| |
| :: |
| |
| int thermal_zone_get_slope(struct thermal_zone_device *tz) |
| |
| This interface is used to read the slope attribute value |
| for the thermal zone device, which might be useful for platform |
| drivers for temperature calculations. |
| |
| :: |
| |
| int thermal_zone_get_offset(struct thermal_zone_device *tz) |
| |
| This interface is used to read the offset attribute value |
| for the thermal zone device, which might be useful for platform |
| drivers for temperature calculations. |
| |
| 1.2 thermal cooling device interface |
| ------------------------------------ |
| |
| |
| :: |
| |
| struct thermal_cooling_device |
| *thermal_cooling_device_register(char *name, |
| void *devdata, struct thermal_cooling_device_ops *) |
| |
| This interface function adds a new thermal cooling device (fan/processor/...) |
| to /sys/class/thermal/ folder as `cooling_device[0-*]`. It tries to bind itself |
| to all the thermal zone devices registered at the same time. |
| |
| name: |
| the cooling device name. |
| devdata: |
| device private data. |
| ops: |
| thermal cooling devices call-backs. |
| |
| .get_max_state: |
| get the Maximum throttle state of the cooling device. |
| .get_cur_state: |
| get the Currently requested throttle state of the |
| cooling device. |
| .set_cur_state: |
| set the Current throttle state of the cooling device. |
| |
| :: |
| |
| void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev) |
| |
| This interface function removes the thermal cooling device. |
| It deletes the corresponding entry from /sys/class/thermal folder and |
| unbinds itself from all the thermal zone devices using it. |
| |
| 1.3 interface for binding a thermal zone device with a thermal cooling device |
| ----------------------------------------------------------------------------- |
| |
| :: |
| |
| int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz, |
| int trip, struct thermal_cooling_device *cdev, |
| unsigned long upper, unsigned long lower, unsigned int weight); |
| |
| This interface function binds a thermal cooling device to a particular trip |
| point of a thermal zone device. |
| |
| This function is usually called in the thermal zone device .bind callback. |
| |
| tz: |
| the thermal zone device |
| cdev: |
| thermal cooling device |
| trip: |
| indicates which trip point in this thermal zone the cooling device |
| is associated with. |
| upper: |
| the Maximum cooling state for this trip point. |
| THERMAL_NO_LIMIT means no upper limit, |
| and the cooling device can be in max_state. |
| lower: |
| the Minimum cooling state can be used for this trip point. |
| THERMAL_NO_LIMIT means no lower limit, |
| and the cooling device can be in cooling state 0. |
| weight: |
| the influence of this cooling device in this thermal |
| zone. See 1.4.1 below for more information. |
| |
| :: |
| |
| int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz, |
| int trip, struct thermal_cooling_device *cdev); |
| |
| This interface function unbinds a thermal cooling device from a particular |
| trip point of a thermal zone device. This function is usually called in |
| the thermal zone device .unbind callback. |
| |
| tz: |
| the thermal zone device |
| cdev: |
| thermal cooling device |
| trip: |
| indicates which trip point in this thermal zone the cooling device |
| is associated with. |
| |
| 1.4 Thermal Zone Parameters |
| --------------------------- |
| |
| :: |
| |
| struct thermal_bind_params |
| |
| This structure defines the following parameters that are used to bind |
| a zone with a cooling device for a particular trip point. |
| |
| .cdev: |
| The cooling device pointer |
| .weight: |
| The 'influence' of a particular cooling device on this |
| zone. This is relative to the rest of the cooling |
| devices. For example, if all cooling devices have a |
| weight of 1, then they all contribute the same. You can |
| use percentages if you want, but it's not mandatory. A |
| weight of 0 means that this cooling device doesn't |
| contribute to the cooling of this zone unless all cooling |
| devices have a weight of 0. If all weights are 0, then |
| they all contribute the same. |
| .trip_mask: |
| This is a bit mask that gives the binding relation between |
| this thermal zone and cdev, for a particular trip point. |
| If nth bit is set, then the cdev and thermal zone are bound |
| for trip point n. |
| .binding_limits: |
| This is an array of cooling state limits. Must have |
| exactly 2 * thermal_zone.number_of_trip_points. It is an |
| array consisting of tuples <lower-state upper-state> of |
| state limits. Each trip will be associated with one state |
| limit tuple when binding. A NULL pointer means |
| <THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips. |
| These limits are used when binding a cdev to a trip point. |
| .match: |
| This call back returns success(0) if the 'tz and cdev' need to |
| be bound, as per platform data. |
| |
| :: |
| |
| struct thermal_zone_params |
| |
| This structure defines the platform level parameters for a thermal zone. |
| This data, for each thermal zone should come from the platform layer. |
| This is an optional feature where some platforms can choose not to |
| provide this data. |
| |
| .governor_name: |
| Name of the thermal governor used for this zone |
| .no_hwmon: |
| a boolean to indicate if the thermal to hwmon sysfs interface |
| is required. when no_hwmon == false, a hwmon sysfs interface |
| will be created. when no_hwmon == true, nothing will be done. |
| In case the thermal_zone_params is NULL, the hwmon interface |
| will be created (for backward compatibility). |
| .num_tbps: |
| Number of thermal_bind_params entries for this zone |
| .tbp: |
| thermal_bind_params entries |
| |
| 2. sysfs attributes structure |
| ============================= |
| |
| == ================ |
| RO read only value |
| WO write only value |
| RW read/write value |
| == ================ |
| |
| Thermal sysfs attributes will be represented under /sys/class/thermal. |
| Hwmon sysfs I/F extension is also available under /sys/class/hwmon |
| if hwmon is compiled in or built as a module. |
| |
| Thermal zone device sys I/F, created once it's registered:: |
| |
| /sys/class/thermal/thermal_zone[0-*]: |
| |---type: Type of the thermal zone |
| |---temp: Current temperature |
| |---mode: Working mode of the thermal zone |
| |---policy: Thermal governor used for this zone |
| |---available_policies: Available thermal governors for this zone |
| |---trip_point_[0-*]_temp: Trip point temperature |
| |---trip_point_[0-*]_type: Trip point type |
| |---trip_point_[0-*]_hyst: Hysteresis value for this trip point |
| |---emul_temp: Emulated temperature set node |
| |---sustainable_power: Sustainable dissipatable power |
| |---k_po: Proportional term during temperature overshoot |
| |---k_pu: Proportional term during temperature undershoot |
| |---k_i: PID's integral term in the power allocator gov |
| |---k_d: PID's derivative term in the power allocator |
| |---integral_cutoff: Offset above which errors are accumulated |
| |---slope: Slope constant applied as linear extrapolation |
| |---offset: Offset constant applied as linear extrapolation |
| |
| Thermal cooling device sys I/F, created once it's registered:: |
| |
| /sys/class/thermal/cooling_device[0-*]: |
| |---type: Type of the cooling device(processor/fan/...) |
| |---max_state: Maximum cooling state of the cooling device |
| |---cur_state: Current cooling state of the cooling device |
| |---stats: Directory containing cooling device's statistics |
| |---stats/reset: Writing any value resets the statistics |
| |---stats/time_in_state_ms: Time (msec) spent in various cooling states |
| |---stats/total_trans: Total number of times cooling state is changed |
| |---stats/trans_table: Cooling state transition table |
| |
| |
| Then next two dynamic attributes are created/removed in pairs. They represent |
| the relationship between a thermal zone and its associated cooling device. |
| They are created/removed for each successful execution of |
| thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device. |
| |
| :: |
| |
| /sys/class/thermal/thermal_zone[0-*]: |
| |---cdev[0-*]: [0-*]th cooling device in current thermal zone |
| |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with |
| |---cdev[0-*]_weight: Influence of the cooling device in |
| this thermal zone |
| |
| Besides the thermal zone device sysfs I/F and cooling device sysfs I/F, |
| the generic thermal driver also creates a hwmon sysfs I/F for each _type_ |
| of thermal zone device. E.g. the generic thermal driver registers one hwmon |
| class device and build the associated hwmon sysfs I/F for all the registered |
| ACPI thermal zones. |
| |
| :: |
| |
| /sys/class/hwmon/hwmon[0-*]: |
| |---name: The type of the thermal zone devices |
| |---temp[1-*]_input: The current temperature of thermal zone [1-*] |
| |---temp[1-*]_critical: The critical trip point of thermal zone [1-*] |
| |
| Please read Documentation/hwmon/sysfs-interface.rst for additional information. |
| |
| Thermal zone attributes |
| ----------------------- |
| |
| type |
| Strings which represent the thermal zone type. |
| This is given by thermal zone driver as part of registration. |
| E.g: "acpitz" indicates it's an ACPI thermal device. |
| In order to keep it consistent with hwmon sys attribute; this should |
| be a short, lowercase string, not containing spaces nor dashes. |
| RO, Required |
| |
| temp |
| Current temperature as reported by thermal zone (sensor). |
| Unit: millidegree Celsius |
| RO, Required |
| |
| mode |
| One of the predefined values in [enabled, disabled]. |
| This file gives information about the algorithm that is currently |
| managing the thermal zone. It can be either default kernel based |
| algorithm or user space application. |
| |
| enabled |
| enable Kernel Thermal management. |
| disabled |
| Preventing kernel thermal zone driver actions upon |
| trip points so that user application can take full |
| charge of the thermal management. |
| |
| RW, Optional |
| |
| policy |
| One of the various thermal governors used for a particular zone. |
| |
| RW, Required |
| |
| available_policies |
| Available thermal governors which can be used for a particular zone. |
| |
| RO, Required |
| |
| `trip_point_[0-*]_temp` |
| The temperature above which trip point will be fired. |
| |
| Unit: millidegree Celsius |
| |
| RO, Optional |
| |
| `trip_point_[0-*]_type` |
| Strings which indicate the type of the trip point. |
| |
| E.g. it can be one of critical, hot, passive, `active[0-*]` for ACPI |
| thermal zone. |
| |
| RO, Optional |
| |
| `trip_point_[0-*]_hyst` |
| The hysteresis value for a trip point, represented as an integer |
| Unit: Celsius |
| RW, Optional |
| |
| `cdev[0-*]` |
| Sysfs link to the thermal cooling device node where the sys I/F |
| for cooling device throttling control represents. |
| |
| RO, Optional |
| |
| `cdev[0-*]_trip_point` |
| The trip point in this thermal zone which `cdev[0-*]` is associated |
| with; -1 means the cooling device is not associated with any trip |
| point. |
| |
| RO, Optional |
| |
| `cdev[0-*]_weight` |
| The influence of `cdev[0-*]` in this thermal zone. This value |
| is relative to the rest of cooling devices in the thermal |
| zone. For example, if a cooling device has a weight double |
| than that of other, it's twice as effective in cooling the |
| thermal zone. |
| |
| RW, Optional |
| |
| emul_temp |
| Interface to set the emulated temperature method in thermal zone |
| (sensor). After setting this temperature, the thermal zone may pass |
| this temperature to platform emulation function if registered or |
| cache it locally. This is useful in debugging different temperature |
| threshold and its associated cooling action. This is write only node |
| and writing 0 on this node should disable emulation. |
| Unit: millidegree Celsius |
| |
| WO, Optional |
| |
| WARNING: |
| Be careful while enabling this option on production systems, |
| because userland can easily disable the thermal policy by simply |
| flooding this sysfs node with low temperature values. |
| |
| sustainable_power |
| An estimate of the sustained power that can be dissipated by |
| the thermal zone. Used by the power allocator governor. For |
| more information see Documentation/driver-api/thermal/power_allocator.rst |
| |
| Unit: milliwatts |
| |
| RW, Optional |
| |
| k_po |
| The proportional term of the power allocator governor's PID |
| controller during temperature overshoot. Temperature overshoot |
| is when the current temperature is above the "desired |
| temperature" trip point. For more information see |
| Documentation/driver-api/thermal/power_allocator.rst |
| |
| RW, Optional |
| |
| k_pu |
| The proportional term of the power allocator governor's PID |
| controller during temperature undershoot. Temperature undershoot |
| is when the current temperature is below the "desired |
| temperature" trip point. For more information see |
| Documentation/driver-api/thermal/power_allocator.rst |
| |
| RW, Optional |
| |
| k_i |
| The integral term of the power allocator governor's PID |
| controller. This term allows the PID controller to compensate |
| for long term drift. For more information see |
| Documentation/driver-api/thermal/power_allocator.rst |
| |
| RW, Optional |
| |
| k_d |
| The derivative term of the power allocator governor's PID |
| controller. For more information see |
| Documentation/driver-api/thermal/power_allocator.rst |
| |
| 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/driver-api/thermal/power_allocator.rst |
| |
| 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. |
| 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. Export Symbol APIs |
| ===================== |
| |
| 4.1. 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. |
| |
| 4.2. 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. |
| |
| 4.3. 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. |
| |
| 5. thermal_emergency_poweroff |
| ============================= |
| |
| On an event of critical trip temperature crossing the thermal framework |
| shuts down the system by calling hw_protection_shutdown(). The |
| hw_protection_shutdown() first attempts to perform an orderly shutdown |
| but accepts a delay after which it proceeds doing a forced power-off |
| or as last resort an emergency_restart. |
| |
| The delay should be carefully profiled so as to give adequate time for |
| orderly poweroff. |
| |
| If the delay is set to 0 emergency poweroff will not be supported. So a |
| carefully profiled non-zero positive value is a must for emergency |
| poweroff to be triggered. |