Re: IRQ issue on graphics card passthrough

["André Weidemann" <Andre.Weidemann@web.de>]

Hi Jan,

On 05.06.2011 10:30, Jan Kiszka wrote:
> 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.

It took me some time to get a native Windows7 running on that machine, 
but you are right. The IRQ under Windows("0xFFFFFFF6 (-10)") is similar 
to the one inside the VM ("0xFFFFFFFE (-2)").

Thank you for your reply.
  André