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SubjectRe: [sodaville] [PATCH 10/15] x86/ioapic: Add OF bindings for IO-APIC
On 01/12/2011 09:07 AM, Sebastian Andrzej Siewior wrote:
>>
>> I'm confused here. Are there multiple ioapic's described by a single
>> device tree node?
>
> Yes, the CE4100 has two IO-APICs. It looks like the first one is
> responsible for the "legacy devices" (like RTC) and the second one is
> used for the "extra devices" like SPI controller, USB, ... The UART
> however is not on the first IO-APIC but on the second.
>
> Those two IO-APICs are not cascaded. The device tree contains the line
> number of device to the io apic. The kernel computes then interrupt
> number based on gsi_base + line_number where gsi_base is incremented by
> the number of entries[0]. This interrupt number (gsi_base + line) is then
> sent via apic bus to lapic which reports it as the active interrupt
> source.
>

That's normal multiple IOAPIC behavior (and multiple IOAPICs is a common
thing), but why use the same device tree node for both?

-hpa


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