I try to use the dpm state, but when I set:

echo 'battery' > /sys/class/drm/card0/device/power_dpm_state

while on battery power, laptop freezes after a time.

I tried to add radeon.dpm=1 and (radeon.bapm=1 or radeon.bapm=0) but it does
not fix. Originally, I discovered this issue using TLP (where you can find the
ticket https://github.com/linrunner/TLP/issues/186).