linux-kernel - Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

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Date:	Tue, 13 Jul 2010 14:59:08 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	zpfeffer@...eaurora.org
Cc:	joro@...tes.org, dwalker@...eaurora.org, andi@...stfloor.org,
	randy.dunlap@...cle.com, mel@....ul.ie, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

On Mon, 12 Jul 2010 22:46:59 -0700
Zach Pfeffer <zpfeffer@...eaurora.org> wrote:

> Joerg Roedel wrote:
> > On Fri, Jul 02, 2010 at 12:33:51AM -0700, Zach Pfeffer wrote:
> >> Daniel Walker wrote:
> > 
> >>> So if we include this code which "map implementations" could you
> >>> collapse into this implementations ? Generally , what currently existing
> >>> code can VCMM help to eliminate?
> >> In theory, it can eliminate all code the interoperates between IOMMU,
> >> CPU and non-IOMMU based devices and all the mapping code, alignment,
> >> mapping attribute and special block size support that's been
> >> implemented.
> > 
> > Thats a very abstract statement. Can you point to particular code files
> > and give a rough sketch how it could be improved using VCMM?
> 
> I can. Not to single out a particular subsystem, but the video4linux
> code contains interoperation code to abstract the difference between
> sg buffers, vmalloc buffers and physically contiguous buffers. The
> VCMM is an attempt to provide a framework where these and all the
> other buffer types can be unified.

Why video4linux can't use the DMA API? Doing DMA with vmalloc'ed
buffers is a thing that we should avoid (there are some exceptions
like xfs though).
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