Variable Clock speed in Linux on STM32mp157c?

[BBeck.1]

It isn't clear to me from this article (https://wiki.st.com/stm32mpu/wiki/Clock_device_tree_configuration_-_Bootloader_specific#cite_note-st.2Cstm32mp1-rcc.txt-1) if I can set operating points for my stm32mp157c part. If not am I stuck setting PLL1 in the tf-a?

Also, can I use the cpufreq-utils to change clock speed on the fly?

Thanks,

Ben

[Olivier GALLIEN]

Hi @BBeck.1​ ,

For DVFS you can refer to

How to change the CPU frequency - stm32mpu

But please be aware that even if the dvfs should work on any chip, this use case will be worst than staying to 650 Mhz (in term of power consumption and in term of cpu efficiency) on a 157C part.

In term of power consumption:

- the main interest off opp is to reduce the power supply. Below 650Mhz, only one supply is qualified.

- It is more efficient to go quickly to IDLE mode (so use cpufreq max) than reducing the cpufreq

In term of cpu efficiency:

- You will lose time switching from one frequency to another, especially if the switch is not done by a simple divider setting (like ST do for 400Mhz opp).

Hope it help

Olivier

[BBeck.1]

Olivier,

Thanks for the reply. My interest in the DVFS was mostly for being able to change frequencies to see how much power this saved me. If I have to do this by changing in the .dtb I will live with that.

Can I do this with just specifying a freq in a single opp?

Thanks,

Ben