How to Change Clock Frequency on GPU?

Products Support DragonBoard 820c
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#1

Hi. We want to try changing the clock frequency numbers for the gpu in the device tree (msm8996.dtsi). We see this for the gpu:
/* This is a safe speed for bring up in all bin levels.
* This isn’t the fastest the chip can go, but we can
* get there eventually */
qcom,gpu-pwrlevels {
compatible = “qcom,gpu-pwrlevels”;
qcom,gpu-pwrlevel@0 {
qcom,gpu-freq = <510000000>;
};
qcom,gpu-pwrlevel@1 {
qcom,gpu-freq = <27000000>;
};
};

What is the range of values we can use. Is it a multiple of some number? Is the one frequency number(510000000) the upper boundary and the other number(270000000) a lower boundary?

Also, can someone tell me if the GPU is dynamically changing clock speed? Can we read the GPU clock speed somehow?

Thanks,
Kim

#2

No sure which tree/branch you’re looking at, but supported frequencies are listed in the operating table: https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/qcom/msm8996.dtsi#L971

You can remove operating points you don’t want to reach.

However I’m not sure this table is actually used in the adreno 5xx driver (cf drivers/gpu/drm/msm/adreno).

#3

Thanks @Loic, I will try those. Do you know of a tool or file location that I can use to read the current GPU frequency? does the frequency change?

Thanks,
Kim