linux-kernel - Re: Define CONFIG_BOUNCE to avoid useless inclusion of bounce buffer logic.

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Date:	Sun, 3 Jun 2007 23:24:39 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Christoph Lameter <clameter@....com>
Cc:	Paul Mackerras <paulus@...ba.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: Define CONFIG_BOUNCE to avoid useless inclusion of bounce buffer logic.

On Wed, May 23, 2007 at 09:03:02PM -0700, Christoph Lameter wrote:
> On Thu, 24 May 2007, Paul Mackerras wrote:
> > Also there is the problem that some drivers use ZONE_DMA allocations
> > because their device can only generate addresses below some limit, but
> > on a platform with an IOMMU there is in fact no restriction on what
> > memory the device can access.
> 
> That problem is to some extend addressed by switching ZONE_DMA off which 
> results in GFP_DMA becoming meaningless. And if GFP_DMA and ZONE_DMA is 
> gone from a platform then the MAX_DMA_ADDRESS inconsistencies are solved 
> since the cause of the inconsistencies has evaporated.

Suffice it to say then that with this approach ARM will _never_ be able
to have ZONE_DMA turned off, even on platforms where there are no DMA
restrictions.  I guess that's something we'll just have to live with.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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