svn commit: r237008 - head/sys/dev/pci

[John Baldwin]

On Tuesday, June 26, 2012 5:14:45 pm Marius Strobl wrote:
> Yes, it does but switching to positive decoding nevertheless is
> problematic in this case. According to the PCI 2.3 specification,
> a child wanting its addresses to be decoded subtractively needs
> to provide special DEVSEL# behavior. It seems that it should work
> for a bridge to actually positively decoding such transactions,
> but I'm not familiar with the physical layer of PCI and thus not
> sure. On the other hand, both the PCI-ISA and PCI-PCI bridges
> in question are ALi/ULi crap and based on fun I had with their
> chips in the past, I also wouldn't be surprised their again being
> a magic bit in the configuration space needing to be set to make
> this work. Unfortunately, I don't have a datasheet for this
> M5249 PCI-PCI bridge. If we'd implement a tunable for changing
> the decoding of subtractive bridges, the way to go would seem to
> be to have it off by default in order to preserve pre-NEW_PCIB/
> r237008 as at this time it's unknown how many bridges are
> affected. If you'd want to keep the new/current behavior by
> default, introducing something like a PCIB_SUBTRACTIVE_FORCED
> flag along a PCI_QUIRK_SUB_FORCED quirk in addition to a
> tuneable defaulting to on probably would be a good idea.

Hmm.  I'm fine with your original change going in then.  I am not really sure 
what the right way to handle this is, and just leaving the windows alone on 
subtractive bridges is probably safest.

-- 
John Baldwin