https://bugzilla.kernel.org/show_bug.cgi?id=51381
--- Comment #16 from Teofilis Martisius Teofilis.Martisius@gmail.com --- Hello,
I can reproduce this problem on v3.15rc8 with power management enabled (radeon.runpm=1). So this hasn't been fixed in v3.15 yet.
v3.15rc8 works OK with radeon.runpm=0 flag
Sincerely, Teofilis Martisius