Where are bus passes with lower than default pass value called?

[Jan Mazur]

Here: http://bxr.su/FreeBSD/sys/kern/subr_bus.c#901
bus_current_pass is set to BUS_PASS_ROOT.

AFAIK autoconfiguration starts here:
http://bxr.su/FreeBSD/sys/mips/mips/autoconf.c#95 and later it
calls BUS_NEW_PASS(root_bus) which calls bus_set_pass(BUS_PASS_DEFAULT).
Why is it called with maximum possible bus pass level - BUS_PASS_DEFAULT?
Where are bus passes with lower pass value called?

JM