Cannot down-clock AMD GPU on Manjaro

So, I have an RX590 FatBoy, which albeit very nice comes factory overclocked which is bad, since it's cooling isn't up to par. On Windows, I lowered the voltages via the Catalyst app and voila - all overheating problems were gone while retaining all the performance I needed.

On Manjaro 18.0 however, I tried setting the speeds in: /sys/class/drm/card0/device/pp_od_clk_voltage but I get an error saying I cannot edit that file.

I tried doing echo "s 7 1209 900" > /sys/class/drm/card0/device/pp_od_clk_voltage but after setting the (correct) values, my GPU just shut-off and I had to reboot.

I have set my boot parameter to amdgpu.ppfeaturemask=0xfffd7fff (and not amdgpu.ppfeaturemask=0xffffffff) based on the output from WattmanGTK.

Sources:

• https://wiki.archlinux.org/index.php/AMDGPU
• https://github.com/BoukeHaarsma23/WattmanGTK