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

Daniel P. Berrangé berrange at redhat.com
Tue Sep 28 08:44:01 UTC 2021


On Sun, Sep 12, 2021 at 08:56:29AM +0530, Ani Sinha wrote:
> This change introduces libvirt xml support for the following two pm options:
> 
> <pm>
>   <acpi-hotplug-bridge enabled='no'/>
>   <acpi-root-hotplug enabled='yes'/>
> </pm>


> +``acpi-hotplug-bridge``
> +   :since:`Since 7.8.0` This option enables or disables BIOS ACPI based hotplug support
> +   for cold plugged bridges. It is available only for x86 guests, both for q35 and pc
> +   machine types. For pc machines, the support is available from `QEMU 2.12`. For q35
> +   machines, the support is available from `QEMU 6.1`. Examples of cold plugged bridges
> +   include PCI-PCI bridges for pc machine types (pci-bridge controller). For q35 machines,
> +   it includes PCIE root ports (pcie-root-port controller). This is a global option that
> +   affects all bridges. No other bridge specific option is required to be specified.

Can you confirm my understanding of the situation..

 - i440fx / PCI topology - hotplug always uses ACPI

 - q35 / PCIe topology - hotplug historically used native PCIe hotplug,
                         but in 6.1 switched to ACPI

Given, the name "acpi-hotplug-bridge",  am I right that this option
has *no* effect, if the q35 machine is using native PCIe hotplug
approach ?  IOW, is it a no-op until 6.1 based machine types for q35 ?

Regards,
Daniel
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