New comment by narodnik on void-packages repository

https://github.com/void-linux/void-packages/issues/53434#issuecomment-2564663129

Comment:
Thanks so much. This is hugely helpful.

I followed your advice, and rebooted kernel 6.6 with the param `amdgpu.ppfeaturemask=0xffffffff`.

Then I open corectrl. My external GPU is card 0, and internal is card 1. For card 0, I see the GPU frequency constantly changing, but it remains fixed at 600 Mhz for card 1.

![card0](https://github.com/user-attachments/assets/e376044e-2671-404d-b348-d3ba21a814b8)
![card1](https://github.com/user-attachments/assets/cda69ac6-4397-4f91-a82a-b5e1b2842df9)

I also tried setting it through the sysfs API:

```
/sys/class/drm/card0/device# cat pp_dpm_sclk 
0: 500Mhz
1: 17Mhz *
2: 2254Mhz
/sys/class/drm/card0/device# echo 0 > pp_dpm_sclk 
/sys/class/drm/card0/device# cat pp_dpm_sclk 
0: 500Mhz
1: 7Mhz *
2: 2254Mhz

/sys/class/drm/card1/device# cat pp_dpm_sclk 
0: 400Mhz 
1: 600Mhz *
2: 2200Mhz 
/sys/class/drm/card1/device# echo 0 > pp_dpm_sclk 
bash: echo: write error: Invalid argument
```