linux-kernel - Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq

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Message-ID: <20120131120922.GD32010@elte.hu>
Date:	Tue, 31 Jan 2012 13:09:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hitoshi Mitake <h.mitake@...il.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Roland Dreier <roland@...estorage.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <James.Bottomley@...allels.com>,
	linux-kernel@...r.kernel.org, hpa@...ux.intel.com
Subject: Re: [PATCH] NVMe: Fix compilation on architecturs without
 readq/writeq


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> >   u64 val;
> >   val = readl(addr);
> >   val |= readl(addr+4) << 32;
> > 
> > is well-defined and must read the low word first - both at the C level
> > *and* at the CPU level. Anything else would be a bug in the
> > architecture "readl()" implementation or the hardware.
> 
> That doesn't make the access atomic to hardware however as a true 64bit
> readq/writeq would be ?
> 
> It seems to me the two are not quite the same semantically

Correct, and that's what the:

	#include <asm/io-inatomic.h>

line in the driver would express.

Thanks,

	Ingo
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