Description of problem:

This is a quote from a description by Ivan posted on axp-list:

I had couple of problems with 4.3.0:
- Detection of the primary adapter is broken. You have to
  set explicit PCI id in XF86Config to get the card detected
  as *secondary*. However, switching to VGA text console won't work then
  (most drivers don't save/restore VGA state for secondary adapters).
- Rather old bug in mga driver (since 4.1.0, IIRC) - the driver
  attempts to read the video ROM *before* enabling it. Naturally,
  this causes annoying machine check on certain platforms.

Nominally on Alpha but it looks from the code that it will really affect
all platforms.  His patch attached.