Radeon driver cases lockout when trying to boot with radeon.dpm=1 with certain cards. Seems like dynamic power management causes the issue and radeon.dpm=0 fixes it.
* HD 6950, 7570M and HD6870 tested
Steps to reproduce:
What exactly does "lockout" mean? What are the symptoms?
Please attach the corresponding dmesg output and/or the kernel .config file. Is all the required microcode installed correctly? (It needs to be in the initrd as well if the driver is loaded from there)
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.
Issue still not fixed...
Early KMS doesn't really change anything