linux-kernel - Re: [PATCH 7/9] ARM: DMA: steal memory for DMA coherent mappings

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Message-Id: <201108121453.05898.arnd@arndb.de>
Date:	Fri, 12 Aug 2011 14:53:05 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Mel Gorman <mel@....ul.ie>,
	Jesse Barker <jesse.barker@...aro.org>,
	Jonathan Corbet <corbet@....net>,
	Shariq Hasnain <shariq.hasnain@...aro.org>,
	Chunsang Jeong <chunsang.jeong@...aro.org>
Subject: Re: [PATCH 7/9] ARM: DMA: steal memory for DMA coherent mappings

On Friday 12 August 2011, Marek Szyprowski wrote:
> 
> From: Russell King <rmk+kernel@....linux.org.uk>
> 
> Steal memory from the kernel to provide coherent DMA memory to drivers.
> This avoids the problem with multiple mappings with differing attributes
> on later CPUs.
> 
> Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
> [m.szyprowski: rebased onto 3.1-rc1]
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>

Hi Marek,

Is this the same patch that Russell had to revert because it didn't
work on some of the older machines, in particular those using
dmabounce?

I thought that our discussion ended with the plan to use this only
for ARMv6+ (which has a problem with double mapping) but not on ARMv5
and below (which don't have this problem but might need dmabounce).

	Arnd
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