From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=tZg2=33=obsidianresearch.com=jgunthorpe@kernel.org>
Return-Path: <SRS0=tZg2=33=obsidianresearch.com=jgunthorpe@kernel.org>
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
Message-ID: <20170419155557.GA8497@obsidianresearch.com>
References: <CAPcyv4it56J8Voo6kV0bBcO3nHsOHYLENpAtONJZTGceDDwNPg@mail.gmail.com>
 <1492381396.25766.43.camel@kernel.crashing.org>
 <20170418164557.GA7181@obsidianresearch.com>
 <cce00131-1f28-27b3-40ab-04f8783f1e5a@deltatee.com>
 <20170418190138.GH7181@obsidianresearch.com>
 <df1351d8-b86c-2e21-1948-4688ece5dc2b@deltatee.com>
 <CAPcyv4gScx6A7vG9VEHpNF41GOy1Nxst7QQ3QC3uZ54bWoxbMg@mail.gmail.com>
 <20170418210339.GA24257@obsidianresearch.com>
 <1492564806.25766.124.camel@kernel.crashing.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <1492564806.25766.124.camel@kernel.crashing.org>
List-ID: <linux-pci.vger.kernel.org>

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