To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Bjorn Helgaas <helgaas@kernel.org>
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Cc: Benjamin Herrenschmidt <benh@kernel.crashing.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>,
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        Dan Williams <dan.j.williams@intel.com>,
        Keith Busch <keith.busch@intel.com>, linux-pci@vger.kernel.org,
        linux-scsi@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-rdma@vger.kernel.org, linux-nvdimm@ml01.01.org,
        linux-kernel@vger.kernel.org, Jerome Glisse <jglisse@redhat.com>
From: Logan Gunthorpe <logang@deltatee.com>
Message-ID: <08c32f0d-6c7c-b65f-6453-dde0d7c173d1@deltatee.com>
Date: Thu, 13 Apr 2017 22:40:46 -0600
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Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
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On 13/04/17 10:16 PM, Jason Gunthorpe wrote:
> I'd suggest just detecting if there is any translation in bus
> addresses anywhere and just hard disabling P2P on such systems.

That's a fantastic suggestion. It simplifies things significantly.
Unless there are any significant objections I think I will plan on doing
that.

> On modern hardware with 64 bit BARs there is very little reason to
> have translation, so I think this is a legacy feature.

Yes, p2pmem users are likely to be designing systems around it (ie
JBOFs) and not trying to shoehorn it onto legacy architectures.

At the very least, it makes sense to leave it out and if someone comes
along who cares they can put in the effort to support the address
translation.

Thanks,

Logan