https://bugs.freedesktop.org/show_bug.cgi?id=90889

--- Comment #2 from lolwoot1234@gmail.com --- Lockout as in no systemd services working, can't ssh into it or switch tty/vt and getting a blank screen.

Here is the systemd journal log when booting with the default radeon.dpm=1: http://pastebin.com/raw.php?i=SRpX7QLK

If by microcode you mean the early KMS/initramfs, yes, it is installed correctly and works with radeon.dpm=0.