From: Robert Hancock <hancockr@shaw.ca>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Flushing writes to PCI devices
Date: Wed, 20 Sep 2006 17:22:43 -0600 [thread overview]
Message-ID: <4511CD43.6060507@shaw.ca> (raw)
In-Reply-To: <fa.gbsNbubc34pqWPOxWCntrwUyt68@ifi.uio.no>
Alan Stern wrote:
> I've heard that to insure proper synchronization it's necessary to flush
> MMIO writes (writel, writew, writeb) to PCI devices by reading from the
> same area. Is this equally true for I/O-space writes (inl, inw, inb)?
> What about configuration space writes (pci_write_config_dword etc.)?
Technically, according to the PCI specification, I/O space writes may be
posted in the host bus bridge (though unlike MMIO space, not at any
other PCI bridges) and would require a read in order to flush them.
However, there seem to be few if any chipsets ever made which actually
do this for I/O writes, and most code in the kernel seems to just assume
it won't happen, so it's probably safe to assume the same.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/
prev parent reply other threads:[~2006-09-20 23:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <fa.gbsNbubc34pqWPOxWCntrwUyt68@ifi.uio.no>
2006-09-20 18:28 ` Flushing writes to PCI devices Alan Stern
2006-09-20 19:10 ` linux-os (Dick Johnson)
[not found] ` <fa.V4O8HKrhUddxYm5+ixVbyZzPybE@ifi.uio.no>
2006-09-20 19:41 ` Bill Waddington
2006-09-20 20:17 ` linux-os (Dick Johnson)
2006-09-21 18:14 ` Bryan O'Sullivan
2006-09-21 18:45 ` Alan Cox
2006-09-21 20:56 ` Roland Dreier
2006-09-21 21:04 ` Bryan O'Sullivan
2006-09-20 22:39 ` Alan Cox
2006-09-20 23:22 ` Robert Hancock [this message]
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