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

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Date:	Wed, 14 Jul 2010 21:34:03 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Zach Pfeffer <zpfeffer@...eaurora.org>
Cc:	Hari Kanigeri <hari.kanigeri@...il.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Andi Kleen <andi@...stfloor.org>,
	Randy Dunlap <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, Jul 12, 2010 at 10:21:05PM -0700, Zach Pfeffer wrote:
> Joerg Roedel wrote:

> > The DMA-API already does this with the help of IOMMUs if they are
> > present. What is the benefit of your approach over that?
> 
> The grist to the DMA-API mill is the opaque scatterlist. Each
> scatterlist element brings together a physical address and a bus
> address that may be different. The set of scatterlist elements
> constitute both the set of physical buffers and the mappings to those
> buffers. My approach separates these two things into a struct physmem
> which contains the set of physical buffers and a struct reservation
> which contains the set of bus addresses (or device addresses). Each
> element in the struct physmem may be of various lengths (without
> resorting to chaining). A map call maps the one set to the other.

Okay, thats a different concept, where is the benefit?

	Joerg

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