linux-kernel - Re: Flushing writes to PCI devices

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Message-Id: <1158872640.1996.9.camel@chalcedony.pathscale.com>
Date:	Thu, 21 Sep 2006 14:04:00 -0700
From:	Bryan O'Sullivan <bos@...pentine.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Bill Waddington <william.waddington@...zmo.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Flushing writes to PCI devices

On Thu, 2006-09-21 at 13:56 -0700, Roland Dreier wrote:
>     Bryan> Yes.  If your device requires that writes to some locations
>     Bryan> in MMIO space be performed in a specific order, you must
>     Bryan> explicitly do this in your driver.  Intel CPUs will flush
>     Bryan> posted writes out of order, for example.
> 
> Really?  Just normal posted PCI writes without using MTRRs or
> write-combining or anything like that?

No, not normal writes, but if you're writing to an area where you've
enabled write combining, it will happen (but not IIRC on AMD x86_64
CPUs).  Sorry for the lack of clarity.

	<b

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