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

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Message-ID: <alpine.LFD.1.10.0805270833060.2958@woody.linux-foundation.org>
Date:	Tue, 27 May 2008 08:35:29 -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, Benjamin Herrenschmidt wrote:
> 
> Yes. As it is today, tg3 for example is potentially broken on all archs
> with newer gcc unless we either add "memory" clobber to readl/writel or
> stick some wmb's in there (just a random driver I picked).
> 
> So Linus, what is your take on that matter ?

Let's just serialize the damn things, and add a memory clobber to them.

Expecting people to fix up all drivers is simply not going to happen. And 
serializing things shouldn't be *that* expensive. People who cannot take 
the expense can continue to use the magic __raw_writel() etc stuff.

			Linus
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