Thermal architecture - Qualcomm Dragonwing Documentation

The thermal architecture shows how the Qualcomm Linux thermal framework interacts with temperature sensors (Tsens) hardware, cooling map interfaces, and user space clients.

Thermal Architecture Diagram

Figure: Thermal architecture Table: Description of the components of thermal architecture

Components of Thermal Architecture	Description
Thermal device tree	A thermal device tree consists of various thermal zones. A thermal zone is configured for every Tsens. Each thermal zone consists of sensor hardware information, different levels of thermal thresholds, and their respective cooling actions. All rules for a thermal zone are defined in the device tree.
Thermal framework	The thermal framework parses the thermal zone rules from the device tree and configures Tsens hardware to generate interrupts when temperature crosses the threshold.
Thermal governor	The thermal governor is a temperature monitor algorithm that controls the temperature of a thermal zone. It mitigates the cooling devices associated with the zone and keeps the temperature within the limit. On receiving an interrupt notification from Tsens hardware, the thermal framework uses a stepwise thermal governor to communicate the cooling actions to the cooling map interface (CPU frequency driver).
Cooling map interface	A cooling map interface is a collection of devices that can be throttled to reduce the temperature of Qualcomm Linux. Every trip instance of the thermal zone is associated with a cooling device. The thermal core framework aggregates all the cooling device instance requests and places the aggregated requests to the cooling device.
User space clients	User space clients use the following interfaces to communicate with the thermal framework: The `sysfs` interface is used to read the temperature of Tsens and kernel trip information. The `Netlink` interface gets information on Tsens temperature notifications.

Thermal Mitigation Policies

Qualcomm Linux uses in-built software and hardware mitigation policies to regulate the device’s thermal behavior. The thermal framework applies the mitigation policies when required and operates through the following policies:

Monitors the thermal response of the system using on-die Tsens
Applies mitigation based on thermal threshold limits defined in the device tree
Implements software throttling, hardware throttling, software shutdown, and hardware shutdown mitigation policies to control temperature

Table: Temperature management techniques and description

Temperature Management Techniques	Description
Software throttling	The Tsens triggers an interrupt whenever the temperature in the system crosses the configured threshold. The thermal framework initiates the following mitigation actions on the CPU, GPU, and NSP in response to the interrupts: Thermal DCVS Reduces the maximum operating frequency if temperature thresholds are crossed Voltage scaling occurs according to clock scaling, which reduces power consumption and temperature in turn CPU idle injection The core is put in the deepest low power state for the configured idle time.
Hardware throttling	In-built hardware runs the thermal mitigation actions ensuring system reliability Reduces CPU and NSP clock speed to quickly recover from high thermal conditions
Software shutdown	The thermal framework initiates graceful shutdown upon receiving interruption from Tsens.
Hardware shutdown	The hardware initiates a device shutdown.

Note: The thermal mitigation techniques are for information purpose only. They help in understanding performance regressions during high thermal conditions. For detailed temperature thresholds for each platform, see Platform Support - Thermal Management.

Next Steps

Configure a thermal zone

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