Date: Mon, 8 Jan 2018 11:29:45 -0700
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Christoph Hellwig <hch@lst.de>, 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?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to
 rdma_rw_ctx_[init|destroy]()
Message-ID: <20180108182945.GG11348@ziepe.ca>
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On Mon, Jan 08, 2018 at 11:17:38AM -0700, Logan Gunthorpe wrote:
 
> >>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.

Not fundamentally, but it lets us solve the bugs the patch introduces
with hfi/etc

> 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.

Well, that is disappointing for now, but I'm OK with the flag in the
RW interface - as long as we all sort of agree it is not desirable and
the SG should self-identify in an ideal someday future world..

Jason