Re: IRQ issue on graphics card passthrough

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-06-04 19:50, André Weidemann wrote:
> Hi,
> as mentioned before I have successfully passed a graphics card from a
> Linux host to VM using qemu-kvm.
> 
> Shortly after starting the VM and before Windows7 initializes the
> graphics card, "info pci" looks like this:
>   Bus  0, device   4, function 0:
>     VGA controller: PCI device 1002:6719
>       IRQ 10.
>       BAR0: 32 bit prefetchable memory at 0xe0000000 [0xefffffff].
>       BAR2: 32 bit memory at 0xfeba0000 [0xfebbffff].
>       BAR4: I/O at 0xc000 [0xc0ff].
>       BAR6: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
>       id "radeon6950"
> 
> After Windows has initialized the graphics card, "info pci" lists the
> following for the graphics card:
>   Bus  0, device  4, function 0:
>     VGA controller: PCI device 1002:6719
>       IRQ 0.
>       BAR0: 32 bit prefetchable memory at 0xe0000000 [0xefffffff].
>       BAR2: 32 bit memory at 0xfeba0000 [0xfebbffff].
>       BAR4: I/O at 0xc000 [0xc0ff].
>       BAR6: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
>       id "radeon6950"
> 
> Notice that the IRQ changed from 10 to 0...
> 
> The graphics card's IRQ under Windows7 is displayed as:
> "0xFFFFFFFE (-2)".

That's not necessarily pointing to a problem, that just means Windows is
using the device in MSI mode. Does it do the same when running natively?

> 
> During another problem of assigning sound cards to a  VM, Jan Kiszka has
> pointed me to a patch that addresses an IRQ issue:
> http://thread.gmane.org/gmane.comp.emulators.qemu/102540
> Unfortuantely it does not help here.

For sure, that patch addresses a legacy interrupt issue, nothing
MSI-related.

Jan


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