Re: Ordering between PCI config space writes and MMIO reads?

Matthew Wilcox
2006-10-24T22:36:34Z

On Tue, Oct 24, 2006 at 02:51:30PM -0700, Roland Dreier wrote:
> > I think the right way to fix this is to ensure mmio write ordering in
> > the pci_write_config_*() implementations. Like this.
>
> I'm happy to fix this in the PCI core and not force drivers to worry
> about this.
>
> John, can you confirm that this patch fixes the issue for you?

Hang on. I wasn't thinking clearly. mmiowb() only ensures the write
has got as far as the shub. There's no way to fix this in the pci core
-- any PCI-PCI bridge can reorder the two.

This is only really a problem for setup (when we program the BARs), so
it seems silly to enforce an ordering at any other time. Reluctantly, I
must disagree with Jeff -- drivers need to fix this.