Is anyone else having Radeon / KMS problems with 3.12.x?
I've just tried to boot 3.12.2 with my HD4890, and the screen went dark as soon as the radeon kernel module loaded. Is there something "special" I need to enable in the kernel .config that I've missed please? Or is this a bug? (I have raised Kernel bug #66241 in Bugzilla already).
There's also this thread on the linux-kernel mailing list, which looks familiar. But there's no follow-up.
There is no special build option i know of. I did have something similar, but i had only blank VTs, X was fine and it was related to missing framebuffer drivers or something (didnt really thought of it again since i ticked some additional options there in the config).
Do you have dpm enabled? If yes, try without it, if no try with it.