linux-kernel - Re: [PATCH] x86: adjust GFP mask handling for coherent allocations

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Message-Id: <20091027181053L.fujita.tomonori@lab.ntt.co.jp>
Date:	Tue, 27 Oct 2009 18:11:11 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	JBeulich@...ell.com
Cc:	mingo@...e.hu, yinghai@...nel.org, tglx@...utronix.de,
	tiwai@...e.de, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org, hpa@...or.com
Subject: Re: [PATCH] x86: adjust GFP mask handling for coherent	 allocations

On Tue, 27 Oct 2009 08:58:14 +0000
"Jan Beulich" <JBeulich@...ell.com> wrote:

> >Well, in the first place, we don't need the #ifdef in Jan's patch. We
> >can always use DMA_BIT_MASK(24) for the fallback device.
> 
> But this one I don't agree with - the purpose of the patch is to not have
> a 24-bit (or 32-bit) mask here unconditionally: It would result in GFP_DMA
> to be forced on for the allocation (which the patch specifically eliminates),

If a driver doesn't want to GFP_DMA, it should set up the
dma_coherent_mask of the device and pass it. In fact, it should do. A
driver that uses the fallback device is broken.

Why can't you fix drivers that use the fallback instead of adding
another hack to the common place?
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