Re: [Xen-devel] [Qemu-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 for INTEL IGD

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, May 22, 2014 at 07:39:36AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > > According to our discussions, I realize we may have some plans or policies
> > > dedicated to how to assign devfn, but to support GFX passthrough for XEN, 
> > > I
> > > think currently it may be a better solution to adopt #1 simply like this:
> > > 
> > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c index eaf3e61..500b3c2
> > > 100644
> > > --- a/hw/i386/pc_piix.c
> > > +++ b/hw/i386/pc_piix.c
> > > @@ -386,7 +386,7 @@ static void pc_xen_hvm_init(QEMUMachineInitArgs
> > > *args)
> > > 
> > >      bus = pci_find_primary_bus();
> > >      if (bus != NULL) {
> > > -        pci_create_simple(bus, -1, "xen-platform");
> > > +        pci_create_simple(bus, PCI_DEVFN(3,0), "xen-platform");
> > >      }
> > >  }
> > >  #endif
> > > 
> > > Then we can go out to plan how to assign devfn in common, is this fine?
> 
> Somewhere else in the thread someone listed a libxl config file snippet
> which is supposed to disable the xen platform device.  Which doesn't
> work with upstream qemu for some reason.
> 
> Searching ...   ah, here:
> http://lists.gnu.org/archive/html/qemu-devel/2014-05/msg03996.html
> 
> So, how about making "xen_platform_pci=0" working correctly ?
> 

You don't want that enabled by default.
Otherwise the Linux (and Windows) drivers won't enable
the PV functionality and we are using the emulated drivers (slow).

> Another useful thing would be to not create the xen platform device in
> case "-nodefaults" was specified on the command line (that switch turns
> off a bunch of other devices present by default: vga, nic, cdrom, ...).
> 
> cheers,
>   Gerd
> 
> 
> 
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