Force X to use second video card so I can pass through first card to XEN VM?

Question

So I am trying to get X to start on my second (PCI 02.00:00) video card and stop using the main card (PCI 1.00:00). I would like to do this because I want to pass through the PCI 1 card to a XEN HVM VM and use the second card as the main display for the dom0. I am led to believe that only the the first card on the PCI bus is compatible with XEM PCI VGA Pass thou.

I'm using CentOS 6 with XEN 4.1; standard X with VESA drivers for now. Both cards are NVIDIA GeForce 8400 series.

I have played around with custom xorg.conf by commenting out the references to the first device and screen, but that does not seem to work. I am also familiar with the PCIBACK module and can get the first video card to show up correctly in the xm pci-list-assignable-devices command.

Solution

You can force an X video driver to use a specific card by adding a line to its device section of xorg.conf called Option "BusId" "x" where x is the PCI bus ID you gave. The format would be something like this. If you don't have any xorg.conf at all adding just these lines to a new file:

Section "Device"
    Identifier      "nvidia"
    Driver          "nvidia"
    BusId           "PCI:2:0:0"
EndSection

Comments

[Admin]

Good luck. I couldn't run the ATI drivers on a Xen kernel with CentOS either... maybe nVidia did it right.

[Jim DeVito]

Thanks Caleb, That is what the xorg.conf looks like minus the BusID part. Looks like it makes total sense. I will try when I get home today and see what happens.