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

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Date:	Fri, 30 May 2008 17:24:27 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
Cc:	Matthew Wilcox <matthew@....cx>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Fri, 2008-05-30 at 08:07 +0200, Haavard Skinnemoen wrote:
> On Fri, 30 May 2008 11:13:23 +1000
> Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > > Currently, this is the only interface I know that can do native-endian
> > > accesses, so if you take it away, I'm gonna need an alternative
> > > interface that doesn't do byteswapping.  
> > 
> > Are you aware that these also don't provide any ordering guarantee ?
> 
> Yes, but I am not aware of any alternative.
> 
> I think the drivers I've written have the necessary barriers (or dma
> ops with implicit barriers) that they don't actually depend on any
> DMA vs. MMIO ordering guarantees. I hope MMIO vs. MMIO ordering is
> guaranteed though?

Only to the same address I'd say.

Ben.


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