GLSDK Thermal framework

GLSDK - DRA7xx Thermal Framework

TI SOC THERMAL MANAGEMENT

TI SOC DRA7XX Thermal Management system consists of Thermal Management Hardware and Linux thermal framework.

Architecture Diagram

The Hardware

The HW TM consist of five thermal zones, namely MPU, GPU, IVA, IPU and DSPEVE.
Each thermal zone has a dedicated sensor and a Bandgaps controller for temperature monitoring and analog to digital conversions.

 Please refer to Figure 18-5. Thermal Management Functional Block Diagram for more details.

HW Cooling Device: A HW cooling device may an onboard fan or an external fan that can be controlled by software running on the CPU. Temperature events supported :

T_ALERT occurs when temperature has reached preset alert point, trigger an interrupt.

T_ALERT - cold event :

Cold event occurs when temperature goes below the preset value of min temperature for alerting the system.

T_ALERT - hot event :

Hot event occurs when temperature goes above the preset value of max temperature for alerting the system.

T_SHUT occurs when temperature has reached preset shutdown point so power down the corresponding CPU, triggers an interrupt.

T_SHUT - cold event :

Cold event occurs when temperature goes below the preset value of min temperature for shutting down the system.

T_SHUT - hot event :

Hot event occurs when temperature goes above the preset value of max temperature for shutting down the system.

The Software

The SW thermal management framework consists of following components:
SW cooling device: A SW cooling device may be a CPUFreq or a similar CPU frequency controller driver that can be used to reduce or increase CPU speeds as per requirement.

The thermal Driver

TI-SOC-THERMAL : The driver configures the hardware, allocates resources (such as irqs, handlers) and binds the cooling devices with thermal zones (external fan/ CPUFreq driver).

The thermal Governor

On DRA7xx we use,
STEP GOVERNOR : Thermal governor takes a decision based on current temperature event and the policy (configured preset values for alerts). For example when temperature rises beyond a preset value, the governor might take a decision to increase cooling by moving CPU frequency to one step lower. The changes in cooling state taken by STEP GOVERNOR are always one step at a time, hence the name.

The Thermal Policy

Includes trip point information and cooling devices states associated with trip points, specified in drivers/staging/ti-soc-thermal/dra752-thermal-data.c

TRIP POINTS: Below mentioned are the trip points configured for all thermal zones,

Trip point 1: Temperature for the first trip point is configured at 110 degree Celsius.

Trip point 2: Temperature for the first trip point is configured at 125 degree Celsius.

Temperature control at Trip Points:

Trip point 1 - Passive control: When the temperature reaches Trip point1, the registered CPU cooling device functions are called. On dra7xx evm it is the CPUFreq driver callback which sets the cooling state to a higher value. A higher cooling state means stepping down to a Lower OPP. DRA7xx supports three OPPs - OPP_NOM(1GHz), OPP_OD(1.2GHz) and OPP_HIGH(1.5GHz)

Cooling states - OPP mapping

Cooling State	OPP
0	OPP_HIGH
1	OPP_OD
2	OPP_NOM

Trip Point 2 - Critical point when temperature reaches Trip point 2, the system is powered down, this is done using the "power off" Linux command/utility.

References

For more internals of generic thermal framework refer to http://events.linuxfoundation.org/sites/events/files/lcjpcojp13_jonghwa.pdf