Early driver development resources

Hello,
	I wrote a driver for a 4 segment digital display device.  I have
a requirement that this device be used as early as possible to report
kernel bootup state.  The driver itself is pretty simple, just using
in/out_be32() and udelay().  The problem is that I don't know how to use
hardware resources in the early stages of booting, before I can call
request_mem_region() and friends.
	Can anyone recommend a book / documentation / reference code /
anything that demonstrates this, or at least could improve my
understanding enough to accomplish this?
	Many thanks,
		Michael