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Date: Fri, 28 Mar 2008 21:17:07 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: use of volatile in iounmap()?
Message-ID: <20080328211707.GD10722@ZenIV.linux.org.uk>
References: <20080328203427.GA14256@uranus.ravnborg.org>
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On Fri, Mar 28, 2008 at 09:34:28PM +0100, Sam Ravnborg wrote:
> While reviewing some CAN driver I stumbled on iounmap
> which has following prototype on x86:
> 
> extern void iounmap(volatile void __iomem *addr);
> 
> I argued that the driver should not use volatile
> but then I cannot explain why the argument to
> iounmap takes a volatile.
> 
> The same goes for many other functions in
> the io*.h headers.
> 
> Grepping the other archs they mostly follow
> same pattern.
> 
> Can anyone explain the rational for volatile in this case.

"Passing a pointer to volatile is allowed, along with passing pointers
to unqualified".