linux-kernel - Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used ring

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Date:   Thu, 29 Oct 2020 11:07:27 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Arnd Bergmann <arnd@...nel.org>
CC:     Sherry Sun <sherry.sun@....com>,
        "Dutt, Sudeep" <sudeep.dutt@...el.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "kishon@...com" <kishon@...com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Dixit, Ashutosh" <ashutosh.dixit@...el.com>
Subject: Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used
 ring

On Wed, Oct 28, 2020 at 04:50:36PM +0100, Arnd Bergmann wrote:
> I think we should try to do something on top of the PCIe endpoint subsystem
> to make it work across arbitrary combinations of host and device
> implementations,
> and provide a superset of what the MIC driver, (out-of-tree) Bluefield endpoint
> driver, and the NTB subsystem as well as a couple of others used to do,
> each of them tunneling block/network/serial/... over a PCIe link of some
> sort, usually with virtio.

VOP is not PCIe-specific (as demonstrated by the vop-loopback patches I
posted a while ago [1]), and it would be a shame for a replacement to be
tied to the PCIe endpoint subsystem.  There are many SOCs out there
which have multiple Linux-capable processors without cache-coherency
between them.  VOP is (or should I say was since I guess it's being
deleted) the closest we have in mainline to easily get generic virtio
(and not just rpmsg) running between these kind of Linux instances.  If
a new replacement framework were to be PCIe-exclusive then we'd have to
invent one more framework for non-PCIe links to do pretty much the same
thing.

[1] https://lore.kernel.org/lkml/20190403104746.16063-1-vincent.whitchurch@axis.com/