linux-kernel - Re: [openib-general] Ordering between PCI config space writes and MMIO reads?

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Message-ID: <adairi8biev.fsf@cisco.com>
Date:	Wed, 25 Oct 2006 07:04:56 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Matthew Wilcox <matthew@....cx>, linux-ia64@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>, linux-kernel@...r.kernel.org,
	openib-general@...nib.org, linux-pci@...ey.karlin.mff.cuni.cz
Subject: Re: [openib-general] Ordering between PCI config space writes and MMIO reads?

 > I'm not sure that can work either. The PCI-X spec is very clear, you
 > must wait for a non-posted completion if you care about order. Doing a
 > config read in the driver as a surrogate flush is not good enough in
 > the general case. Like you say, a pci bridge is free to reorder all
 > in flight non-posted operations.

No, hang on.  Nothing can reorder a dependent read to start after a
write that it depends on, can it?  So a config read of PCI_COMMAND
can't start until the completion of a config write of the same
register, right?

 - R.
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