Prevent duplicate bus_space_map for TURBOchannel?

[Felix Deichmann <m4j0rd0m0%gmail.com@localhost>]

I seek developer advice regarding TURBOchannel support:

Trying to use a TC driver under VAX, I hit the point where a "duplicate" 
bus_space_map is necessary/performed: The generic TC stuff in tc.c, 
especially tc_checkslot(), wants to access memory space by pointers and 
"linearly", so for VAX TC, I must map physical space before (which is 
the same as calling bus_space_map), for example in tc_vsbus.c before 
calling tcattach().
The TC device drivers attached by tc(4) again will call bus_space_map, 
which can lead to multiple allocations of the same region.

What would be the preferred solution here, also regarding the other TC 
platforms?
Basically I'd tend towards code in tc.c which will map for itself there 
when accessing the option ROM, calling tc_badaddr etc., and cleanly 
unmap before attaching children?

Regards,
Felix