Re: [PATCH v5 2/7] hw/i386/acpi-build: Add ACPI PCI hot-plug methods to Q35

[David Gibson]

On Thu, Jun 17, 2021 at 09:07:34PM +0200, Julia Suvorova wrote:
> Implement notifications and gpe to support q35 ACPI PCI hot-plug.
> Use 0xcc4 - 0xcd7 range for 'acpi-pci-hotplug' io ports.
> 
> Signed-off-by: Julia Suvorova <jusual@redhat.com>
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>

I don't know ACPI or x86 particular well, so I could well have missed
something, but..

[snip]
> @@ -392,6 +392,9 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>  
>          if (!pdev) {
>              if (bsel) { /* add hotplug slots for non present devices */
> +                if (pci_bus_is_express(bus) && slot > 0) {
> +                    break;
> +                }
>                  dev = aml_device("S%.02X", PCI_DEVFN(slot, 0));
>                  aml_append(dev, aml_name_decl("_SUN", aml_int(slot)));
>                  aml_append(dev, aml_name_decl("_ADR", aml_int(slot << 16)));
> @@ -516,7 +519,7 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>              QLIST_FOREACH(sec, &bus->child, sibling) {
>                  int32_t devfn = sec->parent_dev->devfn;
>  
> -                if (pci_bus_is_root(sec) || pci_bus_is_express(sec)) {
> +                if (pci_bus_is_root(sec)) {
>                      continue;
>                  }

.. what will this logic do if we encounter a PCIe-switch.  AIUI, it
should be possible to hotplug 1 slot under each downstream port, but
we can't hotplug anything directly under the upstream port.  AFAICT
both the upstream and downstream ports will show up as 'is_bridge'
though.

So, IIUC we want to traverse a PCIe upstream switch port, but not
generate hotplug slots until we encounter the downstream ports below
it.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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