Re: [Xen-users] Passthrough of USB device on ARM without IOMMU ?

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-10-22 at 18:20 +0000, Chris (Christopher) Brand wrote:
> Hi,
>  
> Iâd like to give control of a USB device (or bus â whatever is easiest)
> to domU on my ARM board, which doesnât have an IOMMU.
> It seems that an IOMMU is a prerequisite for passthrough (on ARM, at
> least).

It is a requirement for all platforms with a hardware p2m rather than an
x86/PV guest visible direct-mmu p2m thing. So it is in effect a requirement
for everything apart from x86/PV guests.

>  Is there no way to have it mapped into domU memory space 1:1 ?

No supported way, I think some people have hacked it in, this was discussed
(briefly) in another thread on this list yesterday.

>  Is there something other than passthrough that I should be looking at ?

Exposing the functionality as a PV driver pair, with the physical driver +
PV backend in dom0 would be the usual way.

In this case you could look into enabling the PVUSB drivers on ARM. I'm not
sure what the status of those is off hand, AIUI there is a Linux frontend
and a new QEMU based backend replacing an old out of tree dom0 kernel
backend.

There have also been patches for the toolstack (libxl/xl) side of that on
xen-devel recently.

Ian.

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