Re: [PATCH 0/9][RFC] stackable dma_ops for x86

[Joerg Roedel <joro@8bytes.org>]

On Sun, Sep 28, 2008 at 11:21:26PM +0900, FUJITA Tomonori wrote:
> On Mon, 22 Sep 2008 20:21:12 +0200
> Joerg Roedel <joerg.roedel@amd.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).
> 
> We already handle the latter. This patchset is more flexible but
> seems to incur more overheads.
> 
> This feature will be used for only paravirtualized device passthrough?
> If so, I feel that there is more simpler (and specific) solutions for
> it.

Its not only for device passthrough. It handles also the cases where a
hardware IOMMU does not handle all devices in the system (like in some
Calgary systems but also possible with AMD IOMMU). With this patchset we
can handle these cases in a generic way without hacking it into the
hardware drivers (these hacks are also in the AMD IOMMU code and I plan
to remove them in the case this patchset will be accepted).

Joerg