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

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Message-Id: <20080520.155326.195407196.davem@davemloft.net>
Date:	Tue, 20 May 2008 15:53:26 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	scottwood@...escale.com
Cc:	alan@...rguk.ukuu.org.uk, tpiepho@...escale.com,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code

From: Scott Wood <scottwood@...escale.com>
Date: Tue, 20 May 2008 17:43:58 -0500

> David Miller wrote:
> > The __volatile__ in the asm construct disallows movement of the
> > inline asm relative to statements surrounding it.
> > 
> > The only reason barrier() in kernel.h needs a memory clobber is
> > because of a bug in ancient versions of gcc.  In fact, I think
> > that memory clobber might even be removable.
> 
> Current versions of GCC seem quite happy to move non-asm memory accesses 
> around a volatile asm without a memory clobber; see the test Trent posted.

Indeed, and even the GCC manual is clear about this.
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