In article <20060223204421.GX22989@che.ojctech.com>,
David Young  <dyoung@pobox.com> wrote:
>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?

Yes.

christos