Last night I found that when I lowered rbus_min_start to 0x10000000,
the heretofore useless Cardbus slot on an old HP laptop came to life.
Previously, the kernel grumbled, "cbb0: bad Vcc request", and the cardslot
would not work.

Now, I am trying to understand rbus_min_start does.  Here is what I
have figured out so far; tell me if I have it wrong.  It appears there
are regions of physical address space that are, roughly speaking,
"ineligible" for Cardbus I/O, but the kernel cannot always know what
they are.  (Some "phantom" device may be in the region, or the Cardbus
controller is behind a bridge that will not pass addresses in the region,
so if the Cardbus controller is mapped into that region, it will not
work.)  Ordinarily, such ineligible regions are nearer the bottom of
the address space than the top.  Usually, they are below 1GB.  Hence the
rbus_min_start parameter, and its default, 1GB.  Is that right so far?

Dave

-- 
David Young             OJC Technologies
dyoung@ojctech.com      Urbana, IL * (217) 278-3933