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

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Date:	Wed, 1 Feb 2012 15:35:41 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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, Jan 31, 2012 at 4:23 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> non-atomic sounds good to me too.

You both apparently missed the related discussion that some devices
really do care about order, even if they don't care about atomicity.

So we'd actually have two versions of the header file, one
little-endian, and one big-endian. Then the driver that knows it
doesn't need the atomic 'readq()' that is always defined, but wants a
low-bytes-first version would just do

   #include <linux/io64-little-endian.h>

(or "big-endian" if it wants to read/write high bits first). Most
drivers probably don't care, but apparently NVMe does.

                 Linus
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