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

[Joerg Roedel]

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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