Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines

[Gerd Hoffmann]

  Hi,

> I had understood that the xhci could be a legacy PCI device or a PCI 
> Express device depending on the socket it was plugged into (or was that 
> possibly just someone doing some hand-waving over the fact that 
> obscuring the PCI Express capabilities effectively turns it into a 
> legacy PCI device?).

That is correct, it'll work both ways.

> If that's the case, why do you prefer the default 
> USB controller to be added in a root-port rather than as an integrated 
> device (which is what we do with the group of USB2 controllers, as well 
> as the primary video device)

Trying to mimic real hardware as close as possible.  The ich9 uhci/ehci
controllers are actually integrated chipset devices.  The nec xhci is a
express device in physical hardware.

That is more a personal preference though, there are no strong technical
reasons to do it that way.

cheers,
  Gerd