linux-kernel - Re: Enabling peer to peer device transactions for PCIe devices

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Date:   Mon, 5 Dec 2016 12:06:32 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Stephen Bates <sbates@...thlin.com>,
        Haggai Eran <haggaie@...lanox.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "Suravee.Suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "John.Bridgman@....com" <john.bridgman@....com>,
        "Alexander.Deucher@....com" <alexander.deucher@....com>,
        "Linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Max Gurtovoy <maxg@...lanox.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "serguei.sagalovitch@....com" <serguei.sagalovitch@....com>,
        "Paul.Blinzer@....com" <paul.blinzer@....com>,
        "Felix.Kuehling@....com" <felix.kuehling@....com>,
        "ben.sander@....com" <ben.sander@....com>
Subject: Re: Enabling peer to peer device transactions for PCIe devices

On Mon, Dec 05, 2016 at 12:46:14PM -0700, Jason Gunthorpe wrote:
> In any event the allocator still needs to track which regions are in
> use and be able to hook 'free' from userspace. That does suggest it
> should be integrated into the nvme driver and not a bolt on driver..

Two totally different use cases:

 - a card that exposes directly byte addressable storage as a PCI-e
   bar.  Thin of it as a nvdimm on a PCI-e card.  That's the iopmem
   case.
 - the NVMe CMB which exposes a byte addressable indirection buffer for
   I/O, but does not actually provide byte addressable persistent
   storage.  This is something that needs to be added to the NVMe driver
   (and the block layer for the abstraction probably).