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Date: Thu, 9 Mar 2006 15:43:29 +1100
From: Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] Document Linux's memory barriers [try #2]
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To: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Linus Torvalds <torvalds@osdl.org>, akpm@osdl.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, Alan Cox <alan@redhat.com>, linuxppc64-dev@ozlabs.org
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Jesse Barnes writes:

> So ultimately mmiowb() is the only thing drivers really have to care 
> about on Altix (assuming they do DMA mapping correctly), and the rules 
> for that are fairly simple.  Then they can additionally use 
> read_relaxed() to optimize performance a bit (quite a bit on big 
> systems).

If I can be sure that all the drivers we care about on PPC use mmiowb
correctly, I can reduce or eliminate the barrier in write*, which
would be nice.

Which drivers have been audited to make sure they use mmiowb
correctly?  In particular, has the USB driver been audited?

Paul.