to PCI bridge can be read be evaluating the _BBN method of the host to PCI
device. Unfortunately, there appear to be some lazy/ignorant/moronic/
whatever BIOS writers that return 0 for _BBN for all host to PCI bridges in
the system. On a system with a single host to PCI bridge this is not a
problem as the child bus of that single bridge will be bus 0 anyway.
However, on systems with multiple host to PCI bridges and l/i/m/w BIOS
writers this is a major problem resulting in all but the first host to
PCI bridge failing to attach. So, this adds a workaround.
If the _BBN of a host to PCI bridge is zero and pcib0 already exists
and is not us, the we use _ADR to look up our PCI function and slot
(we currently assume we are on bus 0) and use that to call
host_pcib_get_busno() to try and extract our bus number from config
registers on the host to PCI bridge device. If that fails, then we make
an evil assumption that ACPI's _SB_ namespace lays out the host to PCI
bridges in ascending order and use our pcib unit number as our bus
number.
Approved by: re
9debb53220