https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5a16f7614e33c080bbece39527bde144dcca4ec7
dpm=1 doesn't seem to be explicitly required for the hardware since 3.13. 

If you confirm me it's so (and if we put aside the guy with an HD 4670, the one
with the HD 6950, and the last with a 390x) we can close this bug in my
experience.