linux-kernel - Re: [RFC PATCH 4/4] ARM: Xilinx: Adding Xilinx board support

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Date:	Tue, 3 May 2011 09:52:20 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, johnlinn@...cast.net,
	nicolas pitre <nicolas.pitre@...aro.org>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	grant likely <grant.likely@...retlab.ca>,
	john linn <john.linn@...inx.com>
Subject: Re: [RFC PATCH 4/4] ARM: Xilinx: Adding Xilinx board support

On Tue, May 03, 2011 at 09:58:14AM +0200, Arnd Bergmann wrote:
> On Tuesday 03 May 2011 01:01:18 Russell King - ARM Linux wrote:
> > It is preferable to use the same mapping, as it ensures that you're not
> > going to create incompatible aliases.
> 
> Is aliasing a problem for MMIO mappings? I would think that you can
> ioremap registers anywhere and as often as you want because they are
> never cacheable.

Provided the type and sharability is identical then there is no problem.
I wasn't referring to multiple ioremap()s of the same region - that
should be fine as the same attributes will be used.  If you mix ioremap()
and iotable_init() then you _could_ have problems if you don't use
MT_DEVICE in the iotable.

What I'm basically saying is that mixing the methods of creating these
mappings makes it much easier to get tripped up over these issues.
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