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

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Message-ID: <20061024192210.GE2043@havoc.gtf.org>
Date:	Tue, 24 Oct 2006 15:22:10 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	linux-pci@...ey.karlin.mff.cuni.cz, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org, openib-general@...nib.org,
	John Partridge <johnip@....com>
Subject: Re: Ordering between PCI config space writes and MMIO reads?

On Tue, Oct 24, 2006 at 12:13:19PM -0700, Roland Dreier wrote:
>  1) Is this something that should be fixed in the driver?  The PCI
>     spec allows MMIO cycles to start before an earlier config cycle
>     completed, but do we want to expose this fact to drivers?  Would
>     it be better for ia64 to use some sort of barrier to make sure
>     pci_write_config_xxx() is strongly ordered with MMIO?

The PCI config APIs have traditionally enforced very strong ordering.
Heck, the PCI config APIs often take a spinlock on each read or write;
so they are definitely not intended to be as fast as MMIO.

	Jeff



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