linux-kernel - Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to rdma_rw_ctx

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Message-ID: <20180109171008.GB4518@ziepe.ca>
Date:   Tue, 9 Jan 2018 10:10:08 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christoph Hellwig <hch@....de>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to
 rdma_rw_ctx_[init|destroy]()

On Tue, Jan 09, 2018 at 05:46:40PM +0100, Christoph Hellwig wrote:
> On Mon, Jan 08, 2018 at 12:49:50PM -0700, Jason Gunthorpe wrote:
> > Pretty sure P2P capable IOMMU hardware exists.
> > 
> > With SOC's we also have the scenario that an DMA originated from an
> > on-die device wishes to target an off-die PCI BAR (through the IOMMU),
> > that definitely exists today, and people care about it :)
> 
> Then people will have to help and contribute support for it.

Sure. But my point was all this will have to migrate under the dma_ops
for that to work, so why the resistance to using dma_ops right away?

Jason