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

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Date:	Tue, 31 Jan 2012 12:18:20 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Ingo Molnar <mingo@...e.hu>
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

On Tue, 31 Jan 2012 13:09:22 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * 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.

Why would "inatomic" indicate that - I'm confused. It would imply to me
they were extra specially atomic ?  

(atomos if from the Greek so in- as a prefix isn't the same in- as in
many other words, welcome to English hell - who needs perl)

non-atomic.h might be better, or 'un-atomic' or 'multi-read' or
something ?

Alan
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