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SubjectRe: [PATCH V3 1/3] x86/ioapic: Support hot-removal of IOAPICs present during boot
On Sun, Jun 12, 2016 at 02:06:09PM +0800, Rui Wang wrote:
> On Saturday, June 11, 2016 12:43 AM, Bjorn Helgaas wrote:
> > On Wed, Jun 08, 2016 at 05:32:44PM +0800, Rui Wang wrote:
> > > @@ -1779,8 +1780,12 @@ void __init
> > > pci_assign_unassigned_resources(void)
> > > {
> > > struct pci_bus *root_bus;
> > >
> > > - list_for_each_entry(root_bus, &pci_root_buses, node)
> > > + list_for_each_entry(root_bus, &pci_root_buses, node) {
> > > pci_assign_unassigned_root_bus_resources(root_bus);
> > > +#ifdef CONFIG_X86
> > > + acpi_ioapic_add(ACPI_HANDLE(root_bus->bridge));
> > > +#endif
> >
> > This seems like a strange place to call acpi_ioapic_add(). Your object is to call
> > acpi_ioapic_add() during root bus enumeration.
> >
> > I assume we *can't* call acpi_ioapic_add() from acpi_pci_root_add() at boot
> > time, for some reason you'll explain. But is there a reason we have to call it
> > from pci_assign_unassigned_resources() (where it requires an ifdef) instead
> > of from pcibios_assign_resources(), which is already x86-specific?
> >
> > In acpi_pci_root_add(), we have this:
> >
> > acpi_pci_root_add(...)
> > {
> > ...
> > if (hotadd)
> > acpi_ioapic_add(root);
> >
> > So the obvious question is why don't we just remove the "if (hotadd)"
> > and call acpi_ioapic_add() always.
> >
> > I'm sure the reason is some ordering problem, but we need a comment in
> > acpi_pci_root_add() about why the obvious solution doesn't work.
>
> Yes it's an ording issue. acpi_ioapic_add() and also ioapic_insert_resources()
> have to be later than pci initialization in order to deal with IOAPICs mapped
> on a PCI BAR. There's a comment about this inside pcibios_resource_survey()
> above ioapic_insert_resources(). We can also add a comment inside
> acpi_pci_root_add(), though.
>
> And yes calling acpi_ioapic_add() in pcibios_assign_resources() doesn't require
> ifdef CONFIG_X86. But it'll require a loop to iterate through the root buses,
> and call acpi_ioapic_add() within the loop. pci_assign_unassigned_resources()
> already has that loop. Do you still prefer adding it to
> pcibios_assign_resources() ?

ioapic_insert_resources() is x86-specific, but I'm not sure why; it
seems like it does things that should be applicable to ia64 as well.

acpi_ioapic_add() is not x86-specific, and it is called from
acpi_pci_root_add() for the hot-add case. You're adding an
x86-xpecific call in pci_assign_unassigned_resources(). Why should
the hot-add case be for all arches, but the boot-time case only for
x86?

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