linux-kernel - Re: [Q] Why does dma_alloc_coherent() of ia64 GFP

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Date:	Tue, 11 Nov 2008 14:53:46 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	cl@...ux-foundation.org
Cc:	y-goto@...fujitsu.com, tony.luck@...el.com,
	fujita.tomonori@....ntt.co.jp, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org, joerg.roedel@....com
Subject: Re: [Q] Why does dma_alloc_coherent() of ia64 GFP_DMA?

On Mon, 10 Nov 2008 16:06:52 -0600 (CST)
Christoph Lameter <cl@...ux-foundation.org> wrote:

> On Mon, 10 Nov 2008, Yasunori Goto wrote:
> 
> > Even if a device allows over 4G access and the driver doesn't specify
> > GFP_DMA, dma_alloc_coherent() returns under 4G area.
> 
> GFP_DMA can become 0 for configurations that have
> !CONFIG_ZONE_DMA. Then all of memory is available.
> 
> The call is subarch specific. So f.e. Altix sn_dma_alloc_coherent does
> not set __GFP_DMA.

Is it because it does some kinda address translation
(provider->dma_map_consistent) later? The zone flag is meaningless if
you do sorta address translation (e.g. hardware IOMMU like VT-d).
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