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

["Chen, Tiejun" <tiejun.chen@intel.com>]

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> Sent: Friday, May 16, 2014 10:09 PM
> To: Chen, Tiejun
> Cc: anthony.perard@citrix.com; stefano.stabellini@eu.citrix.com;
> mst@redhat.com; Kelly.Zytaruk@amd.com; peter.maydell@linaro.org;
> xen-devel@lists.xensource.com; weidong.han@intel.com; Kay, Allen M;
> qemu-devel@nongnu.org; jean.guyader@eu.citrix.com;
> anthony@codemonkey.ws; Zhang, Yang Z
> Subject: Re: [Xen-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0
> for INTEL IGD
> 
> On Fri, May 16, 2014 at 06:53:40PM +0800, Tiejun Chen wrote:
> > Some VBIOSs and drivers assume the IGD BDF (bus:device:function) is
> > always 00:02.0, so we need to reserves 00:02.0 for assigned IGD in
> 
> reserve

Fixed.

> 
> > guest.
> >
> > Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> > Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> > ---
> > v2:
> >
> > * Use a common way patch #2 introduce to reserve PCI devfn.
> >
> >  hw/pci-host/piix.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c index
> > ffdc853..b6f49bd 100644
> > --- a/hw/pci-host/piix.c
> > +++ b/hw/pci-host/piix.c
> > @@ -329,6 +329,14 @@ PCIBus *i440fx_init(PCII440FXState
> **pi440fx_state,
> >      s = PCI_HOST_BRIDGE(dev);
> >      b = pci_bus_new(dev, NULL, pci_address_space,
> >                      address_space_io, 0, TYPE_PCI_BUS);
> > +
> > +    /*
> > +     * Some video bioses and gfx drivers will assume the bdf of IGD is
> 00:02.0.
> > +     * So user need to set it to 00:02.0 in Xen configure file explicitly,
> > +     * otherwise IGD will fail to work.
> > +     */
> > +    pci_reserve_pci_devfn(b, PCI_DEVFN(2, 0));
> > +
> 
> And we do this without checking whether PCI passthrough is done. Should it be
> gated on that? Or is the reason you do it unconditionally because you want to
> be able to hot-plug an GFX in?
> 

To be honest currently we can't support hot-plug an GFX :( But I believe this would come soon. And additionally, as you know XEN and KVM have different way to implement pci-passthrough, so looks its not easy to distinguish these scenarios here. And I think now it may be acceptable just to reserve one specific devfn, right? Or could you have a good way, I can try to improve this point.

Thanks
Tiejun