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

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Date:	Wed, 28 May 2008 07:10:21 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.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, 2008-05-27 at 08:35 -0700, Linus Torvalds wrote:
> 
> 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.

Ok.

Do we also remove wmb/rmb/... from drivers then ? :-) I think ia64 would
need to be fixed to make their writel serializing...

Regarding __raw_* their semantics are dodgy ... we might want to provide
something better but it's a different subject.

Cheers,
Ben.


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