linux-kernel - Re: [sodaville] [PATCH 10/15] x86/ioapic: Add OF bindings for IO-APIC

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Date:	Wed, 12 Jan 2011 09:19:53 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	devicetree-discuss@...ts.ozlabs.org, sodaville@...utronix.de,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [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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