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Message-ID: <alpine.DEB.2.22.394.2204181202080.915916@ubuntu-linux-20-04-desktop>
Date: Mon, 18 Apr 2022 12:11:00 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Oleksandr <olekstysh@...il.com>
cc: Christoph Hellwig <hch@...radead.org>,
Stefano Stabellini <sstabellini@...nel.org>,
xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>, Julien Grall <julien@....org>,
"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio
devices in Xen guests
On Mon, 18 Apr 2022, Oleksandr wrote:
> On 16.04.22 09:07, Christoph Hellwig wrote:
>
> Hello Christoph
>
> > On Fri, Apr 15, 2022 at 03:02:45PM -0700, Stefano Stabellini wrote:
> > > This makes sense overall. Considering that the swiotlb-xen case and the
> > > virtio case are mutually exclusive, I would write it like this:
> > Curious question: Why can't the same grant scheme also be used for
> > non-virtio devices? I really hate having virtio hooks in the arch
> > dma code. Why can't Xen just say in DT/ACPI that grants can be used
> > for a given device?
[...]
> This patch series tries to make things work with "virtio" devices in Xen
> system without introducing any modifications to code under drivers/virtio.
Actually, I think Christoph has a point.
There is nothing inherently virtio specific in this patch series or in
the "xen,dev-domid" device tree binding. Assuming a given device is
emulated by a Xen backend, it could be used with grants as well.
For instance, we could provide an emulated e1000 NIC with a
"xen,dev-domid" property in device tree. Linux could use grants with it
and the backend could map the grants. It would work the same way as
virtio-net/block/etc. Passthrough devices wouldn't have the
"xen,dev-domid" property, so no problems.
So I think we could easily generalize this work and expand it to any
device. We just need to hook on the "xen,dev-domid" device tree
property.
I think it is just a matter of:
- remove the "virtio,mmio" check from xen_is_virtio_device
- rename xen_is_virtio_device to something more generic, like
xen_is_grants_device
- rename xen_virtio_setup_dma_ops to something more generic, like
xen_grants_setup_dma_ops
And that's pretty much it.
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