linux-kernel - Re: [PATCH 0/9][RFC] stackable dma

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Message-ID: <20080922183944.GJ24392@amd.com>
Date:	Mon, 22 Sep 2008 20:39:44 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	David Woodhouse <dwmw2@...radead.org>,
	Muli Ben-Yehuda <muli@...ibm.com>,
	Amit Shah <amit.shah@...ranet.com>,
	Ingo Molnar <mingo@...hat.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH 0/9][RFC] stackable dma_ops for x86

On Mon, Sep 22, 2008 at 11:36:19AM -0700, Arjan van de Ven wrote:
> On Mon, 22 Sep 2008 20:21:12 +0200
> Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > Hi,
> > 
> > this patch series implements stackable dma_ops on x86. This is useful
> > to be able to fall back to a different dma_ops implementation if one
> > can not handle a particular device (as necessary for example with
> > paravirtualized device passthrough or if a hardware IOMMU only
> > handles a subset of available devices).
> 
> isn't the right answer here to have a per device DMA ops instead ?

Its implemented using the per-device dma-ops already there. With this
patches there is a list of available dma_ops implementations which are
asked in a particular order if they can handle the device. The first
implementation which returns true is assigned to the device as the
per-device dma_ops structure.

(Hmm, maybe the name stackable is misleading, is "dma_ops multiplexing"
 better?)

Joerg

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