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

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Message-ID: <Pine.LNX.4.64.0811101600490.32282@quilx.com>
Date:	Mon, 10 Nov 2008 16:06:52 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Yasunori Goto <y-goto@...fujitsu.com>
cc:	"Luck, Tony" <tony.luck@...el.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-ia64@...r.kernel.org,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	Joerg Roedel <joerg.roedel@....com>
Subject: Re: [Q] Why does dma_alloc_coherent() of ia64 GFP_DMA?

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.

If you have an IA64 arch that only support 32bit I/O then __GFP_DMA in
dma_alloc_coherent makes sense.





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