https://bugs.freedesktop.org/show_bug.cgi?id=100919
--- Comment #1 from Thomas R. freedesktop-bugs@digital-trauma.de --- I arrived here by way of having a similar problem and bisecting it down to the very same commit. When running a kernel containing it, on my R9 285, modesetting on my two DVI monitors takes very long and results in a weird resolution that looks like 1920x1080 to the system and 960x1080 to the actual device (if its info menu can be trusted). Most other resolutions I tried fail with out of range.