linux-kernel - Re: [PATCH] [POWERPC] Improve (in|out)

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Message-Id: <1211320938.8297.179.camel@pasglop>
Date:	Tue, 20 May 2008 18:02:18 -0400
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Trent Piepho <tpiepho@...escale.com>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code


On Tue, 2008-05-20 at 16:38 -0500, Scott Wood wrote:
> It looks like we rely on -fno-strict-aliasing to prevent reordering 
> ordinary memory accesses (such as to DMA descriptors) past the I/O 
> access.  It won't prevent reordering of memory reads around an I/O
> read, 
> though, which could be a problem if the I/O read result determines
> the 
> validity of the DMA buffer.  IMHO, a memory clobber would be better.

We probably want a full "memory" clobber then...

Ben.


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