I may be doing something wrong, but even with the firmware in the same folder
as the others (/usr/lib/firmware/radeon) and 66551's patch, it still hangs at
the same place.

Here is the content of that folder.
/usr/lib/firmware/radeon$ ls -l CAYMAN*
-rw-r--r-- 1 root root 24148 May 29 20:22 CAYMAN_mc.bin
-rw-r--r-- 1 root root  8704 May 29 20:22 CAYMAN_me.bin
-rw-r--r-- 1 root root  8704 May 29 20:22 CAYMAN_pfp.bin
-rw-r--r-- 1 root root  4096 May 29 20:22 CAYMAN_rlc.bin
-rw-r--r-- 1 root root 31212 Jul 16 21:10 CAYMAN_smc.bin