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

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Message-ID: <20110814075205.GA4986@n2100.arm.linux.org.uk>
Date:	Sun, 14 Aug 2011 08:52:05 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	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>,
	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 Fri, Aug 12, 2011 at 02:53:05PM +0200, Arnd Bergmann wrote:
> 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).

I thought we'd decided to have a pool of available CMA memory on ARMv6K
to satisfy atomic allocations, which can grow and shrink in size, rather
than setting aside a fixed amount of contiguous system memory.

ARMv6 and ARMv7+ could use CMA directly, and <= ARMv5 can use the existing
allocation method.

Has something changed?
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