Re: [Xen-users] vga passthrough with amd radeon r9 285

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 2015-02-02 20:00, Brian Paterni wrote:
> Hi all,
>
> I'm trying to passthrough an AMD Radeon R9 285 to a windows 7 domu, but
> so far have had no luck.
>
> dom0 is debian unstable (linux 3.16 + xen 4.4.1). Though I've found 
> that
> with the qemu-traditional device model removed [1], gfx_passthru is
> currently not possible with debian-provided packages (?)
Set gfx_passthru=0 and pass the GPU as a non-VGA PCI device,
a.k.a. secondary passthrough. You'll have to live with the
boot up splash screen only being visible on the VNC console.
The login screen will show up on the physical GPU once you
have installed the GPU drivers.

Expect all the usual problems with ATI cards, such as
performance degradation and instability if you reboot
the domU.

> 1: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=776742
>
> As a result, I'm begun to compile from source. Since the error message
> I'm receiving mentions the kernel:
>
>    The kernel doesn't support reset from sysfs for PCI device
Harmless and expected, safe to ignore. No need to recompile anything,
nor is rebuilding from source likely to fix it.

> I decided to start with the linux kernel and now have 3.19.0-rc6+
> installed. However this does not fix the problem. I then checked out 
> xen
> from git master, but still, I'm met with the same error.
Ignore the error, it's not important.

> The r9 285 is a relatively new gpu. In fact, there currently is no FOSS
> driver for it (amdgpu has yet to be released).
Also not relevant, you are using the ATI Catalyst driver in Windows 
domU.
No GPU driver should ever be touching the card in dom0, and you should
ensure that that doesn't happen, blacklisting the radeon driver if
necessary to ensure that the device is not tainted by driver 
initialization
before the xen-pciback driver binds to the device.

> Therefore, could the
> non-working gfx_passthru be the result of missing bits in either linux
> or xen that have yet to dropped in? Or am I just 'doing it wrong'.
You are almost certainly just doing it wrong. I had it "working" (as in
as much as the ATI cards do work with PCI passthrough on Xen) with much
older kernels (I currently use 3.14.x) and I use Xen 4.3.x. I gave up
on ATI cards (have a pair of R9 290X cards on the shelf) because of the
reboot issues, but my modified Nvidia 780Ti cards work beautifully.

Gordan

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