Re: [PATCH v3 0/5] Add support for two i386 pm options which control acpi hotplug

On 9/30/21 2:16 AM, Ani Sinha wrote: > On Fri, Sep 24, 2021 at 2:16 AM Laine Stump <laine(a)redhat.com&gt; 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 (that information may well be outdated).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

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.