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

From: Matthew Wilcox <matthew_at_wil.cx>
Date: 2006-10-25 08:36:32
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.
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Received on Wed Oct 25 08:36:51 2006

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