Re: [RFC PATCH v3 0/7] Use ACPI PCI hot-plug for Q35

[Michael S. Tsirkin]

On Thu, Oct 01, 2020 at 05:54:39PM +0200, Julia Suvorova wrote:
> > > Right now I disable native if there is acpihp anywhere, but even if
> > > you enable it for hotplugged devices, native hot-plug will not work.
> >
> > So that's a minor regression in functionality, right?
> > Why is that the case? Because you disable it in ACPI?
> > What if we don't?
> 
> I meant that I disable slot hotplug capabilities, nothing in ACPI
> prevents native from working. Actually, I don't see if there's any
> regression at all. Configurations like hot-plugging downstream port or
> switch to another downstream port haven't worked before, and they
> don't work now. I can enable native for hotplugged bridges, but that
> doesn't make sense, because you won't be able to hot-plug anything to
> it.


You can do the following hack right now:
1- add an upstream port as function 1
2- add a downstream port behind it
3- add some other device (e.g. another upstream port?) as function 0

As this point both ports should be detected.

Going forward we can consider support for adding ports in a hidden state
(not visible to guest) so one won't need an extra function.

> It's not an issue of ACPI, it's PCIe behaviour. Also, native-acpi
> combination may seem bizarre to os

Maybe, maybe not ...
Worth testing whether this works with existing guests.

> (slot enumeration is independent,
> that's why I suggested disabling pcie slot flags).

Yes that part makes sense imho.

-- 
MST