AFAIK, the X "mach64" driver in XF 4.* doesn't care about UseFBDev.
Marc Aurele La France (maintainer of this driver) is basically allergic
to kernel fbdev support.
:-(
I don't know if happened with earlier fbdev versions for you, but one
possibility is that X reconfigures the display base, and possibly more
bits of the card's internal memory map. Either fbdev should restore
that, or adapt to what X set. On R128's and radeon's, this is things
like DISPLAY_BASE_ADDR.
I will have to go threw the X code to fix that :-(
quoted
I have also tried aty128fb with some local patches to get it to
compile for my G4 powerbook. It also doesn't draw the penguin, and it
oopses when X starts, for some reason.
Hrm... I'll have to test radeonfb... It worked yesteday in console (I
don't remember about the penguin) but I didn't try X.
No penguin. That is weird. I get the penguin on my ix86 box.