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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 16 Jan 2019 18:07:53 +0100
Message-ID: <CAK8P3a2ifu9X+SXgoDPSFMYwnKr=Yex8_tD4qRimcOQAhuEa8Q@mail.gmail.com>
Subject: Re: [PATCH 0/8] Virtio-over-PCIe on non-MIC
To:     Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc:     sudeep.dutt@intel.com, ashutosh.dixit@intel.com,
        gregkh <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Vincent Whitchurch <rabinv@axis.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        linux-ntb@googlegroups.com, Jon Mason <jdmason@kudzu.us>,
        Dave Jiang <dave.jiang@intel.com>,
        Allen Hubbe <allenbh@gmail.com>
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On Wed, Jan 16, 2019 at 5:33 PM Vincent Whitchurch
<vincent.whitchurch@axis.com> wrote:
>
> The Virtio-over-PCIe framework living under drivers/misc/mic/vop implements a
> generic framework to use virtio between two Linux systems, given shared memory
> and a couple of interrupts.  It does not actually require the Intel MIC
> hardware, x86-64, or even PCIe for that matter.  This patch series makes it
> buildable on more systems and adds a loopback driver to test it without special
> hardware.
>
> Note that I don't have access to Intel MIC hardware so some testing of the
> patchset (especially the patch "vop: Use consistent DMA") on that platform
> would be appreciated, to ensure that the series does not break anything there.

Hi Vincent,

First of all, I think it is a very good idea to make virtio over PCIe avaialable
more generally. Your patches also make sense here, they mostly fix
portability bugs, so no objection there.

I think we need to take a step back though and discuss what combinations
we actually do want to support. I have not actually read the whole mic/vop
driver, so I don't know if this would be a good fit as a generic interface --
it may or may not be, and any other input would be helpful.

Aside from that, I should note that we have two related subsystems
in the kernel: the PCIe endpoint subsystem maintained by Kishon and
Lorenzo, and the NTB subsystem maintained by Jon, Dave and Allen.

In order to properly support virtio over PCIe, I would hope we can come
up with a user space interface that looks the same way for configuring
virtio drivers in mic, pcie-endpoint and ntb, if at all possible. Have
you looked at those two subsystems?

        Arnd