I also had this issue, uncommenting GRUB_TERMINAL worked for me as well.
Relevant `lspci` output:
01:05.0 VGA compatible controller [0300]: ATI Technologies Inc RC410 [Radeon Xpress 200M] [1002:5a62] Subsystem: Toshiba America Info Systems Device [1179:ff10] Flags: bus master, 66MHz, medium devsel, latency 66, IRQ 17 Memory at d8000000 (32-bit, prefecthable) [size=128M] Memory at d0100000 (32-bit, prefecthable) [size=64K] [snip] Kernel modules: radeon, radeonfb
I also had this issue, uncommenting GRUB_TERMINAL worked for me as well.
Relevant `lspci` output:
01:05.0 VGA compatible controller [0300]: ATI Technologies Inc RC410 [Radeon Xpress 200M] [1002:5a62]
Subsystem: Toshiba America Info Systems Device [1179:ff10]
Flags: bus master, 66MHz, medium devsel, latency 66, IRQ 17
Memory at d8000000 (32-bit, prefecthable) [size=128M]
Memory at d0100000 (32-bit, prefecthable) [size=64K]
[snip]
Kernel modules: radeon, radeonfb