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Date: Tue, 20 May 2008 15:21:13 -0700 (PDT)
From: Trent Piepho <tpiepho@freescale.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code
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Cc: Scott Wood <scottwood@freescale.com>, linuxppc-dev@ozlabs.org,
	linux-kernel@vger.kernel.org
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On Tue, 20 May 2008, Benjamin Herrenschmidt wrote:
> 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...

As far as I could tell, no other arch has a full memory clobber.  I can see
the argument for changing the Linux model to be stricter and less efficient,
but easier to program for.  Not that I entirely agree with it.

But I don't see a good reason for why powerpc should be different than
everything else.