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

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Message-Id: <20091027103758L.fujita.tomonori@lab.ntt.co.jp>
Date:	Tue, 27 Oct 2009 10:38:18 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mingo@...e.hu
Cc:	JBeulich@...ell.com, 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 Mon, 26 Oct 2009 21:19:17 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Jan Beulich <JBeulich@...ell.com> wrote:
> 
> > >>> Ingo Molnar <mingo@...e.hu> 26.10.09 16:22 >>>
> > >* Jan Beulich <JBeulich@...ell.com> wrote:
> > >> And any attempt to eliminate the conditional another way would just 
> > >> introduce a very similar conditional elsewhere; with this having a 
> > >> single user (and foreseeably not ever a second one) I would think this 
> > >> would just make the code less readable.
> > >
> > >There's 3 other current uses of DMA_BIT_MASK(24) in arch/x86 - couldnt 
> > >those use ISA_DMA_BIT_MASK too?
> > 
> > Oh, so you didn't mean me to eliminate the conditional in pci-dma.c, 
> > but just to replace the DMA_BIT_MASK(24) here an elsewhere. Sure, I'm 
> > fine with adding this to the patch.
> 
> Well, can ISA_BIT_MASK fall back to DMA_BIT_MASK(32) on !CONFIG_ISA? If 
> we have ISA support disabled we might as well pretend the whole world is 
> PCI, right?

I don't think that it works. At least, you can't do that with
the DMA_BIT_MASK(24) in arch/x86/kernl/pci-dma.c; it must be
DMA_BIT_MASK(24) even with !CONFIG_ISA.


> That way we'd get rid of that #ifdef in the .c code too.

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.
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