linux-kernel - Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

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Message-ID: <20101009120537.GD20975@n2100.arm.linux.org.uk>
Date:	Sat, 9 Oct 2010 13:05:37 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Felipe Contreras <felipe.contreras@...il.com>,
	Arnd Hannemann <arnd@...dnet.de>,
	Hemant Pedanekar <hemantp@...com>, Greg KH <greg@...ah.com>,
	linux-main <linux-kernel@...r.kernel.org>,
	Han Jonghun <jonghun79.han@...il.com>
Subject: Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

On Sat, Oct 09, 2010 at 01:44:44PM +0200, Uwe Kleine-König wrote:
> Hello,
> 
> On Sat, Oct 09, 2010 at 01:11:26PM +0200, Arnd Bergmann wrote:
> > When you say that "many drivers broken", can you list the ones you know
> > about? It would probably help resolve this the right way.
> I know about the camera stuff on mx3/pcm037.  See
> pcm037_camera_alloc_dma in arch/arm/mach-mx3/mach-pcm037.c.

dma_alloc_coherent, stuffing that into dma_declare_coherent_memory,
which then ioremaps the memory obtained from dma_alloc_coherent, and
is then handed out via a subsequent dma_alloc_coherent call.

So what we end up with is the kernel mapping (normal memory, cacheable),
the DMA coherent mapping (normal memory, non-cacheable) but with the
same shared-ness as the kernel mapping, and finally the ioremap mapping
(device, shared).  So three aliasing mappings all with different
attributes.
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