linux-kernel - Re: Bugfixes: PCI devices get assigned redundant IRQs

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Date:	Fri, 26 Jan 2007 13:54:43 +0100
From:	"Andreas Block" <andreas.block@...-electronics.com>
To:	"Xavier Bestel" <xavier.bestel@...e.fr>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Bugfixes: PCI devices get assigned redundant IRQs

On Fri, 26 Jan 2007 12:00:55 +0100, Xavier Bestel <xavier.bestel@...e.fr>  
wrote:
> On Fri, 2007-01-26 at 11:50 +0100, Andreas Block wrote:
>
>>   	u8 pin, slot;
>> -	int irq;
>> +	int irq = 0;
>
> Aren't there platforms for which irq = 0 is a valid irq ?

As far as I understand the PCI spec, the answer to your question seems to  
be: no
(or I'm missing something).

Don't get me wrong. I'm not talking about system IRQs, but about the value  
of the Interrupt Pin Register in PCI configuration space.

The PCI Local Bus Specification in Revision 3.0 from 3rd February 2004  
says on page 223 about the content of Interrupt Pin register:

Value 0x00: _No_ interrupt
Values 0x01 to 0x04: Interrupt lines A to D
And values 5 to 0xFF are reserved.

So I'd say, the "correction" of greater values than four to a value of one  
seems discussable, too. Because it will break any future changes of the  
PCI spec.

Andreas

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                             _/_/_/_/   Andreas Block
                            _/_/_/_/   Dipl.-Ing.
                           _/_/_/_/   andreas.block@...-electronics.com

       _/_/_/   _/_/_/_/_/_/_/      esd electronic system design gmbh
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                               http://www.esd-electronics.com

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