> > i believe this still doesnt turn off store forwarding. If two PCI commands
> > are written to the same register then they might get 'merged', resulting
> > in the first written command to be lost. This usually doesnt happen, but
> > can happen, and does happen in some cases.
>
> No, the MTRR's turn off store forwarding too.
ok. Then having ioremap_nocache() is completely pointless, because the
MTRRs already say that those areas are UC. (this is a different issue, not
correctness but just interface cleanliness)
> How do we know? Think about DOS. It doesn't _have_ page tables, it depends
> entirely on the MTRR's to do the right thing wrt IO memory.
ok.
> way to feed a networking card is to map a large buffer in PCI memory space
> and then use the MTRR's to mark it write combining but uncached (whatever
> intel calls that combination). That way the core will write combine and
> burst PCI writes, which is what you need for top performance.
The interface will likely be an ioremap_relaxed() done by the driver? Then
we could have ioremap() which does the UC thing we always did. And remove
ioremap_nocache().
-- mingo
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