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

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Date:	Tue, 27 May 2008 15:02:15 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Matthew Wilcox <matthew@....cx>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>, linux-arch@...r.kernel.org,
	scottwood@...escale.com, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, tpiepho@...escale.com
Subject: Re: MMIO and gcc re-ordering issue



On Tue, 27 May 2008, Matthew Wilcox wrote:

> On Tue, May 27, 2008 at 10:38:22PM +0100, Alan Cox wrote:
> > > re-ordering, even though I doubt it will be visible in practice. So if you 
> > > use the "__" versions, you'd better have barriers even on x86!
> > 
> > Are we also going to have __ioread*/__iowrite* ?
> 
> Didn't we already define ioread*() to have loose semantics?

They are supposed to have the same semantics as readl/writel.

And yes, it's "loose", but only when compared to inb/outb (which are 
really very strict, if you want to emulate x86 - an "outb" basically is 
not only ordered, it doesn't even post the write, and waits until it has 
hit the bus!)

		Linus
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