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Date: Tue, 03 Aug 2010 01:04:44 -0700
From: Yinghai Lu <yinghai@kernel.org>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Dave Airlie <airlied@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>
Subject: Re: oops in ioapic_write_entry
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On 08/03/2010 01:00 AM, Eric W. Biederman wrote:
> Yinghai Lu <yinghai@kernel.org> writes:
> 
>>>> Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
>>>> ===================================================================
>>>> --- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
>>>> +++ linux-2.6/arch/x86/kernel/apic/io_apic.c
>>>> @@ -1029,10 +1029,7 @@ static int pin_2_irq(int idx, int apic,
>>>>  	} else {
>>>>  		u32 gsi = mp_gsi_routing[apic].gsi_base + pin;
>>>>  
>>>> -		if (gsi >= NR_IRQS_LEGACY)
>>>> -			irq = gsi;
>>>> -		else
>>>> -			irq = gsi_top + gsi;
>>>> +		irq = gsi_to_irq(gsi);
>>>>  	}
>>>>  
>>>>  #ifdef CONFIG_X86_32
>>
>> what is the point for making irq = gsi_top + gsi when mptable is used instead of acpi?
> 
> Because it is only convention that when mptables are used that the
> first apic pins 0-15 are the ISA irqs.  This thread witnessed and a
> pci irq that came in pin < 16 that was not an ISA irq.  The truly rare
> and exotic case would be for the ISA irqs to be outside the first 16
> ioapic pins but the es7000 did exactly that.

nvidia chipset if acpi is enabled, external pci device will use ioapic from 16 to 23.

if mptable is used, external pci device will not use pin from 16 to 23..., and lot of devices will share same pin.

Yinghai