Comment # 16 on bug 1179387 from Stefan Dirsch

Ok. Apparently with your gfx card, you have no framebuffer device at all. No
idea why. Maybe it's time to get rid of this gfx card. Seriously.

[   164.682] (EE) Unable to find a valid framebuffer device
[...]
[   164.683] (DB) xf86MergeOutputClassOptions unsupported bus type 0
[...]
[   164.698] (EE) FBDEV(0): FBIOPUT_VSCREENINFO succeeded but modified mode
[   164.698] (EE) FBDEV(0): mode initialization failed

And apparently framebuffer on your Matrox AGP cards work. There is no KMS
driver for Matrox G400, and mga X driver no longer work with
current kernel.