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>,
        Bjorn Helgaas <helgaas@kernel.org>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Jens Axboe <axboe@kernel.dk>, Steve Wise <swise@opengridcomputing.com>,
        Stephen Bates <sbates@raithlin.com>, Max Gurtovoy <maxg@mellanox.com>,
        Keith Busch <keith.busch@intel.com>, linux-pci@vger.kernel.org,
        linux-scsi <linux-scsi@vger.kernel.org>,
        linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
        linux-nvdimm <linux-nvdimm@ml01.01.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jerome Glisse <jglisse@redhat.com>
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