To: Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@lst.de>
Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-block@vger.kernel.org,
        Stephen Bates <sbates@raithlin.com>,
        Jens Axboe <axboe@kernel.dk>,
        Keith Busch <keith.busch@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Dan Williams <dan.j.williams@intel.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
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 <20180104221337.GV11348@ziepe.ca>
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 <20180105045031.GX11348@ziepe.ca> <20180108145901.GA10743@lst.de>
 <20180108180917.GF11348@ziepe.ca>
From: Logan Gunthorpe <logang@deltatee.com>
Message-ID: <3daea7fe-f64a-36a9-ca80-0cb4d9acf171@deltatee.com>
Date: Mon, 8 Jan 2018 11:17:38 -0700
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Subject: Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to
 rdma_rw_ctx_[init|destroy]()
Sender: linux-kernel-owner@vger.kernel.org


On 08/01/18 11:09 AM, Jason Gunthorpe wrote:
> It could, if we had a DMA op for p2p then the drivers that provide
> their own ops can implement it appropriately or not at all.

I was thinking of doing something like this. I'll probably rough out a 
patch and send it along today or tomorrow.

>> If at all it should be in the dma_map* wrappers, but for that we'd need
>> a good identifier.  And it still would not solve the whole fake dma
>> ops issue.
> 
> Very long term the IOMMUs under the ops will need to care about this,
> so the wrapper is not an optimal place to put it - but I wouldn't
> object if it gets it out of RDMA :)

Well, creating the extra op doesn't really change anything to the RDMA 
patch in this series. The point is, for the time being, we need to track 
whether we are doing a P2P or normal mapping using a side channel as we 
don't have a good way of tracking it in the SGL at this time.

Adding an extra DMA op is just one way to allow the existing DMA 
providers to opt-in/out.

Logan