Voltage & Thermal Management (VTM) Introduction

VTM Driver Overview

The Voltage and Thermal Management (VTM) system provides the control, status and interrupt generation for the various independent temperature sensors located at different hotspots on the SoC. This allows the kernel to take actions based on thermal events configured via the kernel’s device tree. Driver Features

Sysfs Monitoring

One of the most basic roles the VTM system can give the kernel is temperature readings (in milliCelcius) in the sysfs filesystem.

cat /sys/class/thermal/thermal_zone*/temp

Running this command on your SoC will print each temperature in milliCelcius for that region on the SoC.

Thresholds, Triggers and Cooling

We can also program up to 3 threshold temperatures, 2 for greater than thresholds and 1 for a less than threshold, to allow the VTM to alert the kernel to take action. For example when the 1st threshold is exceeded the kernel can be alerted to begin reducing the voltage and clocks speed of CPUs, allowing the SoC’s overall temperature to stabilize. If the SoC temperature continues to increase we can then use the 2nd threshold to take more aggressive action. For example we could issue a poweroff command to turn the device off completely once the 2nd threshold is exceeded.

Threshold temperatures can be set in the kernel with the values we define inside the device tree. This can be used for:

  1. To set a ‘critical’ temperature, where the kernel will poweroff the SoC

  2. To signal a ‘passive’ alert in kernel in event of overheating

  3. To lower the MPU frequency by registering cpufreq driver as a cooling device. cpufreq does DFS on the MPU to set the frequency specified in OPP table in the device tree. For more details, see DFS.

/* From arch/arm64/boot/dts/ti/k3-j7200-thermal.dtsi */

    mpu_thermal: mpu-thermal {
            polling-delay-passive = <250>; /* milliseconds */
            polling-delay = <500>; /* milliseconds */
            thermal-sensors = <&wkup_vtm0 1>;

            trips {
                    mpu_crit: mpu-crit {
                            temperature = <125000>; /* milliCelsius */
                            hysteresis = <2000>; /* milliCelsius */
                            type = "critical";

                    mpu_alert0: mpu_alert {
                            temperature = <55000>; /* millicelsius */
                            hysteresis = <5000>; /* millicelsius */
                            type = "passive";

            cpu_cooling_maps: cooling-maps {
                    map0 {
                            trip = <&mpu_alert0>;
                            cooling-device =
                            <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;

This node will instruct the kernel to periodically poll this temperature sensor and to shutdown the SoC once it has exceeded 125 degrees Celsius. And will enable cooling using DFS by cpufreq-dt driver on the MPU at 55 degrees Celsius. Finding More Information

More information can be found for this VTM device inside the Technical Reference Manual for your device or the device tree binding documentation in the kernel’s source.