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Date: Tue, 7 Mar 2006 12:06:02 -0700
From: Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH] Document Linux's memory barriers
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To: "linux-os (Dick Johnson)" <linux-os@analogic.com>
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On Tue, Mar 07, 2006 at 01:54:33PM -0500, linux-os (Dick Johnson) wrote:
> This might be a good place to document:
>     dummy = readl(&foodev->ctrl);
> 
> Will flush all pending writes to the PCI bus and that:
>     (void) readl(&foodev->ctrl);
> ... won't because `gcc` may optimize it away. In fact, variable
> "dummy" should be global or `gcc` may make it go away as well.

static inline unsigned int readl(const volatile void __iomem *addr)
{
	return *(volatile unsigned int __force *) addr;
}

The cast is volatile, so gcc knows not to optimise it away.