Re: [Qemu-devel] [PATCH] q35/mch: implement extended TSEG sizes

[Gerd Hoffmann]

On Fri, 2017-06-09 at 13:40 +0200, Paolo Bonzini wrote:
> 
> On 08/06/2017 21:55, Michael S. Tsirkin wrote:
> > We don't have room anywhere in PCI config space. Laszlo makes
> > argument
> > why it's safe for this device based on spec but it's anyone's guess
> > whether current and future software will follow spec.  In short,
> > going
> > anywhere near the emulated device has a potential to break some
> > drivers.
> 
> There are no such drivers.  The MCH and PCH are only touched by the
> firmware, not by the OS.

Yea.  That is *exactly* the reason why I think simply using the 0x50
offset probably works fine in practice even though I suspect on
physical hardware it might be some undocumented register.  Much of the
stuff in the host bridge pci config space is firmware territory, and we
run qemu specific firmware *anyway*.

cheers,
  Gerd