Re: [PATCH v3 3/5] conf: introduce acpi-hotplug-bridge and acpi-root-hotplug pm options

On Tue, Sep 28, 2021 at 02:35:47PM +0530, Ani Sinha wrote: Yes, I think it will be important to understand if 'shpc' becomes relevant when ACPI hotplug is disabled for PCI Oh, I mis-read and didn't realize this was controlling the QEMU "acpi-pci-hotplug-with-bridge-support" configuration. With this in mind I think the naming is somewhat misleading. Setting it to off would give users the impression that hotplug is disabled, which is not the case for Q35 at least. It is just switching to a different hotplug implementation. At least from Q35 pov, I think it would be better to call it hotplug-mode="acpi|pcie" so it is clear that no matter what value it is set to, hotplug is still available. If we also consider PIIX, then depending on the answer wrt shpc above, we might want one of hotplug-mode="acpi|pcie|none" hotplug-mode="acpi|pcie|shpc" I see that is refering to pie-root-port gaining native_hotplug=bool in 6.1 You say the guest OS always chooses native over ACPI - is that reqiired in the spec, or is that just how some common guest OS have choosen to impl it today ? Right so we have * PIIX4 - acpi-root-pci-hotplug=bool Whether hotplug is enabled for the root bridge or not <target hotplug="on/off"> for pci-root controller - acpi-pci-hotplug-with-bridge-support=bool Toggles support for ACPI based hotplug across all bridges. If disabled will there will be no hotplug at all for PIIX4 ? Or does 'shpc' come into play in that scenario ? PIIX combinations (1) acpi-root-pci-hotplug=yes acpi-pci-hotplug-with-bridge-support=yes - All bridges have hotplug (2) acpi-root-pci-hotplug=yes acpi-pci-hotplug-with-bridge-support=no - No bridges have hotplug (3) acpi-root-pci-hotplug=no acpi-pci-hotplug-with-bridge-support=yes - All bridges except root have hotplug (4) acpi-root-pci-hotplug=no acpi-pci-hotplug-with-bridge-support=no - No bridges have hotplug. Essentially identical to (2) * Q35 - acpi-pci-hotplug-with-bridge-support=bool Toggles support for ACPI based hotplug. If disabled native PCIe hotplug is activated instead * pcie-root-port - hotplug=bool Toggles whether hotplug is enabled on the port. Affects either native and ACPI based hotplug, depending on what acpi-pci-hotplug-with-bridge-support=bool is set to ? <target hotplug="on/off"> for pcie-root-port controller - native_hotplug=bool Can be used to also enable native hotplug, even when ACPI based hotplug is globally enabled. IOW only really relevant when acpi-pci-hotplug-with-bridge-support=true Q35 combinations (1) acpi-pci-hotplug-with-bridge-support=yes pcie-root-port.hotplug=yes pcie-root-port.native_hotplug=yes ports have both ACPI + native hotplug, guest prefers native (2) acpi-pci-hotplug-with-bridge-support=yes pcie-root-port.hotplug=no pcie-root-port.native_hotplug=yes ports have no hotplug, despite native_hotplug=yes IIUC (3) acpi-pci-hotplug-with-bridge-support=yes pcie-root-port.hotplug=yes pcie-root-port.native_hotplug=no ports have ACPI hotplug only (4) acpi-pci-hotplug-with-bridge-support=yes pcie-root-port.hotplug=no pcie-root-port.native_hotplug=no ports have no hotplug (5) acpi-pci-hotplug-with-bridge-support=no pcie-root-port.hotplug=yes pcie-root-port.native_hotplug=yes ports have native hotplug (6) acpi-pci-hotplug-with-bridge-support=no pcie-root-port.hotplug=no pcie-root-port.native_hotplug=yes ports have no hotplug, despite native_hotplug=yes IIUC (7) acpi-pci-hotplug-with-bridge-support=no pcie-root-port.hotplug=yes pcie-root-port.native_hotplug=no ports have no hotplug, despite hotplug=yes IIUC (8) acpi-pci-hotplug-with-bridge-support=no pcie-root-port.hotplug=no pcie-root-port.native_hotplug=no ports have no hotplug Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|