https://bugzilla.kernel.org/show_bug.cgi?id=56441
--- Comment #8 from Alex Deucher alexdeucher@gmail.com --- (In reply to Carlo Rizzardo from comment #7)
Now, with the kernel ubuntu currently uses, it works without any problem.
Good.
I don't know if it has to do with this or is useful but while turning on ubuntu displays for about a second the message "[ 17.074823] radeon 0000:01:00.0: Invalid ROM contents"
You can ignore that.