linux-kernel - Re: MMIO and gcc re-ordering issue

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Message-ID: <alpine.LFD.1.10.0805271028520.2958@woody.linux-foundation.org>
Date:	Tue, 27 May 2008 10:31:14 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	David Miller <davem@...emloft.net>, linux-arch@...r.kernel.org,
	scottwood@...escale.com, linuxppc-dev@...abs.org,
	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	tpiepho@...escale.com
Subject: Re: MMIO and gcc re-ordering issue

On Tue, 27 May 2008, Linus Torvalds wrote:
> 
> Here's a UNTESTED patch for x86 that may or may not compile and work, and 
> which serializes (on a compiler level) the IO accesses against regular 
> memory accesses.

Ok, so it at least boots on x86-32. Thus probably on x86-64 too (since the 
code is now shared). I didn't look at whether it generates much bigger 
code due to the potential extra serialization, but some of the code 
generation I looked at looked fine.

IOW, it doesn't at least create any _obviously_ worse code, and it should 
be arguably safer than assuming the compiler does volatile accesses the 
way we want it to.

		Linus
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