Interesting.  Late last week, after recompiling my kernel I found that
when X started up, I had nothing but garbage on the screen.  I had been
fooling around with the video settings on the card (Cirrus Logic) under
DOS, but the garbage persisted after a power cycle.  Alas, I did not
perform enough experiments to precisely determine a cause, but I decided
to try doing without the aperature driver, which required a quick recompile
with INSECURE turned on (so that /dev/mem would work) and during that
reboot I forced the graphics card into "mode 0".  I believe there is no
NVRAM of any sort on the card, in which case the mode fiddling under DOS
is irrelevant; if that is wrong, it could be either that or a malfunctioning
aperature driver.  At any rate, using /dev/mem it now appears to work for
me.  If you're using the aperature driver, you might try using /dev/mem
instead.