Re: [Qemu-devel] Attaching PCI devices to the PCIe root complex

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> Yes but, same as in the initial design,
> it really makes it user's problem.
> 
> So we'd have
> virtio-net-pci-conventional
> virtio-net-pci-express
> virtio-net-pci-integrated
> 
> 
> All this while users just really want to say "virtio"
> (that's the expert user, what most people want is for guest to be faster).

And for the actual device emulation it makes almost no difference.  xhci
exists in express and integrated variants too.  The qemu-emulated device
calls pcie_endpoint_cap_init() unconditionally, so the express endpoint
capability shows up even if you plug it into the root bus.  That should
be handled better.  But I think that would be the only difference in the
xhci code.  And even that could be handled in the pci core, for example
by making pcie_endpoint_cap_init a nop unless the device is actually is
a express endpoint from the bus topology point of view.

Maybe PCIDeviceClass->is_express should move to PCIDevice and
PCIDeviceClass should get a supports_express field instead.

cheers,
  Gerd