Unable to get Spread Spectrum working on STM32MP157

[jvog.sen]

Hello,

I tried to enable spread spectrum for PLL1 by adding a csg line to the TF-A DeviceTree:

pll1:st,pll@0 {
	compatible = "st,stm32mp1-pll";
	reg = <0>;
	cfg = < 1 49 0 1 1 PQR(1,0,0) >;
	csg = < 60 600 SSCG_MODE_CENTER_SPREAD >;
};

I tried several different settings including one without any csg configuration. Each measurement (spectrum analyzer + nerafield probe) shows the exact same spectrum.

Are there any additional settings I need to apply?

[PatrickF]

Hi @jvog.sen​ ,

To get PLL1 static settings to be taken into account, you need to suppress the &cpu0_opp_table

node in both TF-A and Linux Device Tree (with opp_table, TF-A and Linux will compute PLL1 settings at runtime an ignore the pll1 node).

See https://wiki.st.com/stm32mpu/wiki/How_to_change_the_CPU_frequency#Overview

Regards

In order to give better visibility on the answered topics, please click on 'Select as Best' on the reply which solved your issue or answered your question. See also 'Best Answers'