linux-kernel - Re: oops in ioapic_write

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Date:	Tue, 03 Aug 2010 02:15:07 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Dave Airlie <airlied@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: oops in ioapic_write_entry

Yinghai Lu <yinghai@...nel.org> writes:

> On 08/03/2010 01:56 AM, Eric W. Biederman wrote:
>> Yinghai Lu <yinghai@...nel.org> writes:
>> 
>>> On 08/03/2010 01:00 AM, Eric W. Biederman wrote:
>>>> Yinghai Lu <yinghai@...nel.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.
>> 
>> Exactly.  Pins < 16 are not necessarily ISA irqs, and can be possibly
>> shared level triggered PCI irqs.  Unfortunately there are strange
>> boards like the es7000 where pins > 16 are ISA irqs.
>> 
>> The other thing that is gained by having pin_2_irq always remap pins <
>> 16 is we can get away with the numerous hard codes in the arch/x86 and elsewhere
>> that assume irq < 16 is an ISA irq.
>
> how about this one ?

You can't share an edge triggered ISA irq, it isn't really physically
possible.  So I don't see how this extra complexity will change anything.

Eric


> ---
>  arch/x86/kernel/apic/io_apic.c |   31 ++++++++++++++++++++++++++++---
>  1 file changed, 28 insertions(+), 3 deletions(-)
>
> 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
> @@ -1013,6 +1013,28 @@ static inline int irq_trigger(int idx)
>  	return MPBIOS_trigger(idx);
>  }
>  
> +static int shared_with_legacy(int apic, int pin)
> +{
> +	int i;
> +
> +	for (i = 0; i < mp_irq_entries; i++) {
> +		int bus = mp_irqs[i].srcbus;
> +
> +		if (!test_bit(bus, mp_bus_not_pci))
> +			continue;
> +
> +		if (mp_ioapics[apic].apicid != mp_irqs[i].dstapic)
> +			continue;
> +
> +		if (mp_irqs[i].dstirq != pin)
> +			continue;
> +
> +		return mp_irqs[i].srcbusirq;
> +	}
> +
> +	return -1;
> +}
> +
>  static int pin_2_irq(int idx, int apic, int pin)
>  {
>  	int irq;
> @@ -1029,10 +1051,13 @@ static int pin_2_irq(int idx, int apic,
>  	} else {
>  		u32 gsi = mp_gsi_routing[apic].gsi_base + pin;
>  
> -		if (gsi >= NR_IRQS_LEGACY)
> +		if (gsi >= NR_IRQS_LEGACY) {
>  			irq = gsi;
> -		else
> -			irq = gsi_top + gsi;
> +		} else {
> +			irq = shared_with_legacy(apic, pin);
> +			if (irq < 0)
> +				irq = gsi_top + gsi;
> +		}
>  	}
>  
>  #ifdef CONFIG_X86_32
--
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