My point was, it's not inherently necessary in order to use MMCONFIG.
I'm not saying the checks (unreachable_devices and
pci_mmcfg_check_hostbridge) aren't useful or needed with many real
machines. However, in the event that type1 access isn't available we
just skip all those checks because we have no other option. It would
indeed be a pretty broken spec if there was no way to bootstrap with it
even under ideal conditions..
I can't really disagree that MMCONFIG doesn't have great advantages for
most devices (though it likely is faster on a lot of platforms, which
may be significant if the device does lots of config space accesses). So
for the moment, avoiding using it except where necessary will likely
work out (except if some system does indeed puke on mixing type1 and
MMCONFIG).
However, what Microsoft is doing with Vista may eventually make a
difference in the future. Many hardware vendors seem to use the testing
strategy of "test with latest Windows version. Works OK? Ship it." If
Vista decides that MMCONFIG is good to use all the time, then type1
access support is likely going to a) end up less tested and b) probably
deleted entirely in time. We've seen it before - it used to be that not
using ACPI was the safe option on most hardware with Linux. Now you
pretty much have to use it because the manufacturers only test with it
enabled. I've seen at least one board where the interrupt routing was
completely broken with ACPI off, because they obviously only tested in
Windows..
-
