https://bugzilla.kernel.org/show_bug.cgi?id=116251
--- Comment #1 from Michel Dänzer michel@daenzer.net --- Duplicate of bug 115321.
(In reply to Eugene Shalygin from comment #0)
With kernel 4.5.1 the Radeon card is always on. Reverting 5a427809cd9143bef89ee3110f45e84f37484218 fixes the problem.
I did warn Greg KH about this regression, but it looks like he backported the change anyway. :(