linux-kernel - Re: [tip:x86/irq] x86, acpi/irq: Handle isa irqs that are not identity mapped to gsi's.

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Date:	Tue, 08 Jun 2010 15:20:02 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	Feng Tang <feng.tang@...el.com>,
	Len Brown <len.brown@...el.com>,
	Jacob Pan <jacob.jun.pan@...el.com>
Subject: Re: [tip:x86/irq] x86, acpi/irq: Handle isa irqs that are not identity
 mapped to gsi's.

On 06/07/2010 02:05 PM, H. Peter Anvin wrote:
> On 05/05/2010 02:32 AM, Eric W. Biederman wrote:
>>>
>>> can you use legacy_irq->nr_legacy_irqs instead of NR_IRQS_LEGACY ?
>>
>> No. legacy_irq->nr_legacy_irqs is just for dealing with hardware that
>> does not have i8259 pics.
>>
> 
> I don't know if it is "just" for this purpose.  Quite on the contrary.
> In fact, the fact that NR_IRQS_LEGACY is showing up at all looks like a
> real problem.
> 
>> Here I am reserving 16 irqs above the gsi range in case we get a
>> weird gsi to isa irq mapping.
> 
> But that 16 is exactly because those are the (platform-specific) legacy
> IRQs.
> 
>> Currently the sfi spec doesn't mention anything explicitly.  I
>> took a quick read through it and sfi and I presume Moorestown
>> is talking about non pci irqs.  So I would not be surprised
>> if we didn't have isa device drivers running on platforms
>> without i8259s.
> 
> I'm confused about the above.  Where do you see any mention to fixed
> (ISA) IRQs in SFI or Moorestown?  Jacob tells me they don't exist.
> 
>> Currently the code had a small bug dealing with multiple ioapics and
>> the spec really is incomplete about how you map irqs from pci devices
>> to interrupts.  So it looks like SFI and Moorestown are more a lab
>> experiment than real hardware at the moment.  So I expect when
>> it gets completely fleshed out we will have to jump through a
>> similar set of hoops as we do with acpi to ensure the first 16
>> irqs are not used for anything except isa irqs.
> 
> Moorestown hardware certainly exists, although not all the support is
> upstream yet.
> 
> Either which way, anything which perpetuates NR_IRQS_LEGACY as a
> compile-time constant is begging for people to get things wrong, and it
> really needs to go away.

yes, it should be replaced legacy_irq->nr_legacy_irs to make Moorestown to have sane irq index.

otherwise gsi_to_irq will mapping all [0, 15] to start from nr_irqs_gsi.

Thanks

Yinghai
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