linux-kernel - Re: [PATCH] ARM: Gemini: Add support for PCI BUS

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Date:	Mon, 6 Dec 2010 13:18:24 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Sergei Shtylyov <sshtylyov@...sta.com>
Cc:	Paulius Zaleckas <paulius.zaleckas@...il.com>,
	Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: Gemini: Add support for PCI BUS

On Monday 06 December 2010, Sergei Shtylyov wrote:
> > There are many differences between readl and __raw_readl, including
> 
> > * __raw_readl does not have barriers and does not serialize with
> >    spinlocks, so it breaks on out-of-order CPUs.
> > * __raw_readl does not have a specific endianess, while readl is
> >    fixed little-endian,
> 
>     I know I'm late but readl()/writel() are CPU-endian, not LE.

If that was the case, it would be a bug. readl/writel is defined to be
the same endianess as PCI, which is little-endian. Otherwise you would
not be able to use any PCI devices on big-endian ARM machines. The
definition of readl is

#define readl(addr) __le32_to_cpu(__raw_readl(addr))

which converts the little-endian I/O register into a native endian
CPU register.


	Arnd
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