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

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Message-ID: <alpine.LFD.1.10.0805271456060.2958@woody.linux-foundation.org>
Date:	Tue, 27 May 2008 14:59:28 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	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, 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* ?

I doubt there is any reason to. Let's just keep them very strictly 
ordered. 

> Also is the sematics of __readl/__writel defined for all architectures -
> I used it ages ago in the i2o drivers for speed and it got removed
> because it didn't build on some platforms.

Agreed - I'm not sure the __ versions are really worth it. We have them, 
but the semantics are subtle enough that most drivers will never care 
enough to really use them.

I would suggest using them mainly for architecture-specific drivers, on 
architectures where it actually matters (which is not the case on x86).

		Linus
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