Re: [Qemu-devel] [RESEND PATCH 2/6] memory: introduce AddressSpaceOps and IOMMUObject

[David Gibson]

On Tue, Nov 14, 2017 at 11:21:59AM +0100, Auger Eric wrote:
> Hi Yi L,
> 
> On 03/11/2017 13:01, Liu, Yi L wrote:
> > From: Peter Xu <address@hidden>
> > 
> > AddressSpaceOps is similar to MemoryRegionOps, it's just for address
> > spaces to store arch-specific hooks.
> > 
> > The first hook I would like to introduce is iommu_get(). Return an
> > IOMMUObject behind the AddressSpace.
> 
> David had an objection in the past about this method, saying that
> several IOMMUs could translate a single AS?
> 
> https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg01610.html
> 
> On ARM I think it works in general:
> In
> https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/pci/pci-iommu.txt,
> it is said
> "a given PCI device can only master through one IOMMU"

That's using a platform specific meaning of what "one IOMMU" means.
In general what's several IOMMUs and what's one IOMMU which responds
to several address regions is not distinguishable from the device's
point of view.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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