https://bugs.freedesktop.org/show_bug.cgi?id=84017
--- Comment #10 from Michel Dänzer michel@daenzer.net --- (In reply to comment #9)
I haven't touched "pci=nomsi". It looks like MSI is not working at all on this chipset ...
That's why Alex suggested disabling MSI completely via pci=nomsi. radeon.msi only affects the radeon driver.