DVFS on STM32MP1

[JensOnOctavo]

Hi,

I’m hoping to do a little testing on how to reduce power consumption by changing the A7 core frequencies on the OSD32MP1-RED Dev board. This article

https://wiki.st.com/stm32mpu/wiki/How_to_change_the_CPU_frequency

makes it looks like DVFS is supported on the STM32MP1 processor. I’m pretty inexperienced at this stuff, but I did find the stm32mp157c-osd32mp1-red.dtsi file in the source code for the debian build in the SDK (in the /osd32mp1-workspace/kernel/linux-4.19.94/arch/arm/boot/dts folder), and I added the OPP points to it (600MHz, 400MHz, 300MHz, 24MHz, all at 1.2V). I compiled and flashed the RED board, and I do see the frequencies showing up when I run the command

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

(although weirdly they show up as 24000 300000 400000 600000 650000, so maybe listed as kHz?)

Anyway the scaling_governor is set to performance, not ondemand, and I don’t know how to change it. So my question is: is DVFS supported by the chip, and by the debian linux used in the Octavo SDK? Any help or tips on how to enable it in the simplest way possible? Thanks!

[Eshtaartha Basu]

Hello JensOnOctavo,

DVFS is supported by OSD32MP15x SiPs.

DVFS is officially supported by OpenSTLinux v2.0.0 (kernel v5.4.x) and later versions.
See “Main NEW features of the STM32MP15-ecosystem-v2.0.0 release” of
https://wiki.st.com/stm32mpu-ecosystem-v2/wiki/STM32MP15_ecosystem_release_note_-_v2.0.0?action=view

As indicated here (https://github.com/octavosystems/osd32mp1-debian), Octavo’s SDK currently uses Linux Kernel v4.19
which does not support DVFS. Although scaling governors and related options are visible under sysfs, they
don’t function, as necessary. We’re working on updating our SDK. Please check back later for updates – https://octavosystems.com/octavo_products/osd32mp1-red/

Meanwhile, you can use DVFS on OpenSTLinux v2.0.0 (kernel v5.4.x):
https://wiki.st.com/stm32mpu-ecosystem-v2/wiki/STM32MP1_Developer_Package
You can select v2.0.0 from the drop-down menu of Linux, U-Boot and TF-A download pages.

Although DVFS is also supported by newer versions of OpenSTLinux, we have validated only v2.0.0 on our devices.

You can change the governor by writing to “scaling_governor” attribute under /sys/devices/system/cpu/cpufreq/policyX/

Example:

debian@localhost:/sys/devices/system/cpu/cpufreq/policy0$ cat scaling_governor
performance

debian@localhost: sudo su

root@localhost:/sys/devices/system/cpu/cpufreq/policy0# echo “” > scaling_governor
root@localhost:/sys/devices/system/cpu/cpufreq/policy0# cat scaling_governor
ondemand

You can read CPU’s real time speed by reading “scaling_cur_freq” attribute
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq

You can measure CPU’s core voltage by probing VDD_CORE pin using a multimeter.

For more detailed information on all CPU scaling parameters and how to modify them, read:
https://github.com/STMicroelectronics/linux/blob/v5.10-stm32mp/Documentation/admin-guide/pm/cpufreq.rst

• This reply was modified 3 years, 4 months ago by Eshtaartha Basu.

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