> The probeget routine starts as follows:
> 
> 	set	KERNBASE, %o2
> 	cmp	%o0, %o2		! if addr < KERNBASE
> 	blu	Lfsbadaddr		!	go return error
> 
> What is the point of comparing against KERNBASE?

probeget() is supposed to be passed a virtual address.

On a sun4, obio.c used a temporary virtual address to establish a
mapping to the <bus, physical address> from the configuration file
before calling the device "match" routine. Within the xxmatch routine,
the device can use this address to frob the hardware. If successful,
a permanent map is made either by obio before calling xxattach() or by
xxattach() itself (depending on the needs of the driver).

-pk