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1. Framework purpose[edit source]
The purpose of this article is to introduce the Thermal framework.
Thermal framework is a subsystem made for handling thermal sensors and cooling devices, it is made of 3 subsystems:
- thermal zone
- cooling device
- thermal-sensor via hwmon API or thermal API
2. System Overview[edit source]
2.1. Component description[edit source]
- thermal-zone is a container used to describe all thermal data for the platform
- thermal framework offers an API to read temperature, and to handle thresholds with interrupts.
- hwmon framework offers an API to read temperature for polling usage, a sysfs but, no threshold.
- cooling-device device is used to dissipate heat either
- actively for example with a FAN controlled by GPIOs
- passively via OPP by forcing a lower CPU voltage or frequencies as a cooling state.
2.2. thermal-zone details[edit source]
The thermal zone is also responsible for
- driving cooling devices depending on thermal sensor information,
- handling a critical trip point that consist of calling shutdown,
- polling thermal sensors that does not handle trips points with IRQs (that are implemented under hwmon framework).
A system may contains several thermal zones. For example one for CPU, one for GPU. Each zone is made of:
- a thermal sensor with some polling periods descriptions,
- some active or passive trip points with a temperature and hysteresis for each,
- a cooling map that describe the action for each trip point.
2.3. API description[edit source]
The Thermal API is not documented in the Linux Kernel documentation.
3. Configuration[edit source]
3.1. Kernal configuration[edit source]
The Thermal API is activated by default in ST deliveries. Nevertheless, if a specific configuration is required, you can use Linux Menuconfig tool: Menuconfig or how to configure kernel and select:
[*] Device Drivers -->
[*] Thermal drivers (THERMAL [=y]) -->
[*] STMicroelectronics thermal drivers
[*] Hardware Monitoring support (HWMON [=y])
3.2. Devicetree configuration[edit source]
The thermal zone is represented by the Thermal zone binding[1]
The thermal sensor is represented by the Thermal sensor binding[2]
The thermal cooling device is represented by the Thermal cooling device binding[3]
4. How to use the Thermal framework[edit source]
5. Use cases[edit source]
A typical use case is passive power dissipation, consisting in limiting CPU frequency when the temperature of the CPU is too high.
6. How to trace and debug the framework[edit source]
6.1. How to monitor[edit source]
6.2. How to trace[edit source]
There are no specific traces for this framework.
6.3. How to debug[edit source]
There are no specific debug means for this framework.