On Thu, Sep 30, 2021 at 18:52 Laine Stump <la...@redhat.com> wrote: > On 9/30/21 2:16 AM, Ani Sinha wrote: > > On Fri, Sep 24, 2021 at 2:16 AM Laine Stump <la...@redhat.com> wrote: > >> > >> On 9/11/21 11:26 PM, Ani Sinha wrote: > >>> The above two options are only available for qemu driver and that too > for x86 > >>> guests only. Both of them are global options. > >>> > >>> ``acpi-hotplug-bridge`` option enables or disables ACPI hotplug > support for cold > >>> plugged bridges. Examples of cold plugged bridges include PCI-PCI > bridge > >>> (pci-bridge controller) for pc machines and pcie-root-port controller > for q35 > >>> machines. The corresponding commandline options to qemu for x86 guests > are: > >> > >> The "cold plugged bridges" term here throws me for a loop - it implies > >> that hotplugging bridges is something that's supported, and I think it > >> still isn't. Of course this is just the cover letter, so it won't go > >> into git anywhere, but I think it should be enough to say "enables ACPI > >> hotplug into non-root bus PCI bridges/ports". > > > > I think emphasizing cold plugged bridges is important as Igor (CC'd) > > has clarified in the other email on patch #3 of this series. > > Okay, so the implication in Igor's email is that a) it is possible to > hotplug a pcie controller, but b) any controller that is hotplugged will > not have ACPI enabled. Note though that libvirt doesn't allow > hotplugging *any* PCI controller, since we were told long ago that no OS > will actually rescan the PCI topology when this is done, and so the new > controller wouldn't be usable anyway. (that information may well be > outdated).
>From i440fx side all empty ports in the pci root controller are described as hotplug capable from ACPI. So I do not see why we cannot hotplug a pci bridge in one of the pci root ports and OS should be able to detect it without reboot. I have not tried it though. > > I think if you're going to mention that it is specifically for > "cold-plugged bridges" then you should also 1) define what > "cold-plugged" means, i.e. "(PCI controllers that were present in the > domain definition when the guest was first started"), and 2) note that > "ACPI is not enabled for bridges that are hot-plugged (but currently > libvirt doesn't support hotplugging a pci controller anyway)" or > something like that. > >