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

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Date:	Mon, 10 Nov 2008 15:57:40 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Robin Holt <holt@....com>
cc:	Andi Kleen <andi@...stfloor.org>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	"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, Robin Holt wrote:

> I am not sure what is be referred to here, but all of an Altix's memory is
> DMA capable with the exception of the stuff covered by the MSPEC driver
> (that is uncached memory).  There are certainly all sort of special
> requirements for doing transfers on Altix to eliminate memory ordering
> problems, but nothing specific that I recall related to address ranges
> and DMA.

But then ZONE_DMA has nothing to do with memory being dmaable or not.
ZONE_DMA is for legacy devices that cannot do DMA to all of memory.
I vaguely remember having stuffed all the memory into ZONE_NORMAL at some
point. ZONE_DMA vanishes for Altix configurations.

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