linux-kernel - RE: [PATCHv2 3/4] mm: vmalloc: add VM_DMA flag to indicate areas used by dma-mapping framework

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Message-id: <001d01cd3caa$a05d0510$e1170f30$%szyprowski@samsung.com>
Date:	Mon, 28 May 2012 10:19:39 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'KOSAKI Motohiro' <kosaki.motohiro@...il.com>,
	'Paul Mundt' <lethal@...ux-sh.org>
Cc:	'Minchan Kim' <minchan@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	'Kyungmin Park' <kyungmin.park@...sung.com>,
	'Arnd Bergmann' <arnd@...db.de>,
	'Russell King - ARM Linux' <linux@....linux.org.uk>,
	'Chunsang Jeong' <chunsang.jeong@...aro.org>,
	'Krishna Reddy' <vdumpa@...dia.com>,
	'Konrad Rzeszutek Wilk' <konrad.wilk@...cle.com>,
	'Hiroshi Doyu' <hdoyu@...dia.com>,
	'Subash Patel' <subashrp@...il.com>,
	'Nick Piggin' <npiggin@...il.com>
Subject: RE: [PATCHv2 3/4] mm: vmalloc: add VM_DMA flag to indicate areas used
 by dma-mapping framework

Hello,

On Sunday, May 27, 2012 2:35 PM KOSAKI Motohiro wrote:

> On Thu, May 24, 2012 at 8:28 AM, Paul Mundt <lethal@...ux-sh.org> wrote:
> > On Thu, May 24, 2012 at 02:26:12PM +0200, Marek Szyprowski wrote:
> >> On Tuesday, May 22, 2012 9:08 AM Minchan Kim wrote:
> >> > Hmm, VM_DMA would become generic flag?
> >> > AFAIU, maybe VM_DMA would be used only on ARM arch.
> >>
> >> Right now yes, it will be used only on ARM architecture, but maybe other architecture will
> >> start using it once it is available.
> >>
> > There's very little about the code in question that is ARM-specific to
> > begin with. I plan to adopt similar changes on SH once the work has
> > settled one way or the other, so we'll probably use the VMA flag there,
> > too.
> 
> I don't think VM_DMA is good idea because x86_64 has two dma zones. x86 unaware
> patches make no sense.

I see no problems to add VM_DMA64 later if x86_64 starts using vmalloc areas for creating 
kernel mappings for the dma buffers (I assume that there are 2 dma zones: one 32bit and one
64bit). Right now x86 and x86_64 don't use vmalloc areas for dma buffers, so I hardly see
how this patch can be considered as 'x86 unaware'.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


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