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Date: Wed, 19 Apr 2017 09:55:57 -0600
From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dan Williams <dan.j.williams@intel.com>,
        Logan Gunthorpe <logang@deltatee.com>,
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Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
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On Wed, Apr 19, 2017 at 11:20:06AM +1000, Benjamin Herrenschmidt wrote:

> That helper wouldn't perform the actual iommu mapping. It would simply
> return something along the lines of:
> 
>  - "use that alternate bus address and don't map in the iommu"

I was thinking only this one would be supported with a core code
helper..

>  - "use that alternate bus address and do map in the iommu"
>  - "proceed as normal"

.. because I don't have an idea how a core code helper could figure
out what the platform needs for the above two ..

I think many of the iommu platforms will need to construct their own
bus address in the iommu, and we already have easy access to the CPU
address.

Presumably once a transcation passes through the iommu it needs to be
using the CPU address for the target bar, otherwise things are going
to be ambiguous..

Jason