[Xen-devel] Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just because there's no local APIC

[ebiederm@xxxxxxxxxxxx (Eric W. Biederman)]

Jeremy Fitzhardinge <jeremy@xxxxxxxx> writes:

> On 06/18/09 12:27, Eric W. Biederman wrote:
>>> The only actual exception I know of is Xen's replacement of the physical
>>> local APIC with a paravirtualized interrupt interface.
>>>     
>>
>> No one ever has.  Xen doesn't have I/O APICs either.  Not in any real
>> sense.  Xen just has devices that looking like I/O apics if you don't
>> look close.
>>   
>
> Well, if acpi_pci_irq_lookup() and friends return the right things
> without having parsed the MADT and set up the secondary state, then we
> should be fine either way.
>
> acpi_irq_model gets tested in all sorts of random places, so I wonder if
> we'll need to set it to ACPI_IRQ_MODEL_IOAPIC (or something else?) to
> make things work properly.

And this is where things get interesting.  Xen strictly speaking has
already made that decision.  Unless you support non APIC mode it
should always be ACPI_IRQ_MODEL_IOAPIC.

But Xen runs the hardware so Xen knows, and Xen should be running
all of the acpi and what not to make it happen.

> Hm, and principle we just get the SCI gsi from the FADT, but there's all
> that other mucking about with it in the MADT processing... Wonder what
> needs to happen there...

Good question.  What does the domU case do?

Eric


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