I recently bumped from 3.13.2 to 3.13.3, and upon bootup, the 'radeon' driver didn't seem to kick-in like usual. I've tried rebooting a couple of times but to no avail. When I booted up the 3.13.2 kernel once again, everything worked fine. I'm not sure what all information you'll need to diagnose what this problem will be, but I'm happy to provide whatever is needed. For starters, my video line in grub.conf (Legacy GRUB) is: video=radeon:mtrr:3,ywrap,1366x768-32@60 What I want to stress is that this behavior started with kernel 3.13.3, as everything worked as intended in 3.13.2. My system is loosely based on Gentoo although it is almost entirely upstream packages built by hand now, so there wouldn't be any distro modifications present between kernel versions. All I did for the new kernel is copy .config over from 3.13.2 and ran and exited menuconfig to freshen the file. Please let me know any other information that will help diagnose this problem! Thank you!
Oh how embarrassing, for some reason or another menuconfig overwrote my .config file even though I copied it over, the driver simply wasn't being built. My bad, you can close this ticket.