https://bugs.freedesktop.org/show_bug.cgi?id=76490
--- Comment #89 from Maxim Sheviakov mrader3940@gmail.com --- (In reply to Tobias Droste from comment #88)
Doesn't fix it for me, it still locks up at boot with dpm enabled and the quirk removed.
[drm] initializing kernel modesetting (PITCAIRN 0x1002:0x6810 0x174B:0xE271 0x00)
Have you put the new firmware files to your initramfs/initrd? Check replies above.