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

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Message-ID: <1313656073.2254.23.camel@computer2>
Date:	Thu, 18 Aug 2011 09:27:53 +0100
From:	Tixy <tixy@...t.co.uk>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	'Arnd Bergmann' <arnd@...db.de>, 'Ankita Garg' <ankita@...ibm.com>,
	'Daniel Walker' <dwalker@...eaurora.org>,
	'Russell King - ARM Linux' <linux@....linux.org.uk>,
	'Jesse Barker' <jesse.barker@...aro.org>,
	'Mel Gorman' <mel@....ul.ie>,
	'Chunsang Jeong' <chunsang.jeong@...aro.org>,
	'Jonathan Corbet' <corbet@....net>,
	linux-kernel@...r.kernel.org,
	'Michal Nazarewicz' <mina86@...a86.com>,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	'Kyungmin Park' <kyungmin.park@...sung.com>,
	'KAMEZAWA Hiroyuki' <kamezawa.hiroyu@...fujitsu.com>,
	'Shariq Hasnain' <shariq.hasnain@...aro.org>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: RE: [PATCH 7/9] ARM: DMA: steal memory for DMA coherent mappings

On Wed, 2011-08-17 at 15:06 +0200, Marek Szyprowski wrote:
[...]
> > > Maybe for the first version a static pool with reasonably small size
> > > (like 128KiB) will be more than enough? This size can be even board
> > > depended or changed with kernel command line for systems that really
> > > needs more memory.
> > 
> > For a first version that sounds good enough. Maybe we could use a fraction
> > of the CONSISTENT_DMA_SIZE as an estimate?
> 
> Ok, good. For the initial values I will probably use 1/8 of 
> CONSISTENT_DMA_SIZE for coherent allocations. Writecombine atomic allocations
> are extremely rare and rather ARM specific. 1/32 of CONSISTENT_DMA_SIZE should
> be more than enough for them.

For people who aren't aware, we have a patch to remove the define
CONSISTENT_DMA_SIZE and replace it with a runtime call to an
initialisation function [1]. I don't believe this fundamentally changes
anything being discussed though.

-- 
Tixy

[1] http://www.spinics.net/lists/arm-kernel/msg135589.html

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