Re: [Xen-users] Help with VGA passthrough

[Brian Menges <bmenges@xxxxxxxxxx>]

So FINALLY after a lot of frustration, it all came down to a damn cable.

I was using a DVI-DisplayPort cable, which apparently this graphics card 
doesn't handle well. I also was trying HDMI without enabling (odd... I thought 
it would enable all on its own if it was the only thing plugged in).

Long story short, Finally while reluctantly trying a straight through DVI 
cable, things worked, and I was able to get over to an HDMI-DVI cable which 
suits my needs.

Thanks for everyone's help.

- Brian Menges
Principal Engineer, DevOps
GoGrid | ServePath | ColoServe | UpStream Networks

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxx] 
On Behalf Of Gordan Bobic
Sent: Wednesday, June 25, 2014 02:20
To: xen-users@xxxxxxxxxxxxx
Subject: Re: [Xen-users] Help with VGA passthrough

On 2014-06-25 09:45, Daniel E. Shub wrote:
> On Wednesday 25 June 2014 08:45:07 Gordan Bobic wrote:
>
>> In terms of device capture, reboot the machine and look at lspci
> -vvv. If
>
>> anything other than pciback is the driver attached to your GPU, it
> isn't
>
>> going to work. If the radeon driver touched the card it has been
> tainted
>
>> and until the bus reset method is implemented it won't work. You
> will need
>
>> to remove the radeon driver from your initrd, blacklist it in
>
>> /etc/modprobe.d/, create a configuration file for xen-pciback in
> there to
>
>> make it capture the PCI devices you will be passing through, and
> create a
>
>> script in /etc/sysconfig/modules/ to modprobe xen-pciback and AFTER
> that
>
>> modprobe radeon if your primary GPU also uses that driver.
>
> I don't have to do any of this with my 5450. My machine has two 5450's
> and no other video cards so maybe that is why it works. I let my
> machine boot up as normal and then just use xl pci-assignable-add
> before I want to start a DomU with the video card as secondary
> passthrough.

Does your machine load the radeon driver? If you don't boot into GUI and have 
the radeon driver blacklisted then most of this wouldn't matter. I quite 
clearly remember that if anything touched the GPU before the domU driver it 
wouldn't work at all. It is plausible something has changed since I tried it, 
though, such as the radeon driver in dom0 resetting the card to a clean state 
when it unloads.

Gordan

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