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Date: Tue, 16 Dec 2008 11:21:08 +1100
From: Paul Mackerras <paulus@samba.org>
To: Trent Piepho <tpiepho@freescale.com>
Subject: Re: [PATCH] POWERPC: MTD: Add cached map support to physmap_of MTD
	driver
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Cc: linuxppc-dev@ozlabs.org, linux-mtd@lists.infradead.org,
	Trent Piepho <xyzzy@speakeasy.org>
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Trent Piepho writes:

> The MTD system supports operation where a direct mapped flash chip is
> mapped twice.  The normal mapping is a standard ioremap(), which is
> non-cached and guarded on powerpc.  The second mapping is used only for
> reads and can be cached and non-guarded.  Currently, only the pxa2xx
> mapping driver makes use of this feature.  This patch adds support to the
> physmap_of driver on PPC32 platforms for this cached mapping mode.

Note that having two mappings of the same physical address that differ
in cacheability is a programming error according to the PowerPC
architecture.

Do you know that the processor implementations where you want to do
this can cope with having two mappings with different cacheability?

Paul.