linux-kernel - Re: IRQ problem with IO-APIC and plx9056-based data capture board

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Date:	Thu, 12 Jul 2007 23:16:27 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Brett Boren <brett.boren@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: IRQ problem with IO-APIC and plx9056-based data capture board

Brett Boren wrote:
> I have a plx9056-based data capture board that works with the winXP
> drivers (based off of the win32 plx sdk) but does not work with the
> linux driver provided to me. The board constitently gets 0xa (IRQ 10)
> in the INTERRUPT_LINE register but the IO-APIC reports IRQ 49 to the

You should not be looking at PCI_INTERRUPT_LINE at all. That is set by 
the BIOS and applies only for XT-PIC interrupt routing, not for IOAPIC. 
It is not necessarily relevant to the interrupt numbers used by Linux at 
all.

> kernel. To add to the confusion when an interrupt is triggered it
> arrives on IRQ 17 causing an irq disable. When run with `noapic` on
> the kernel bootline a consistent irq 10 is observed and the driver
> behaves correctly. When `irqpoll` is given the driver behaves
> correctly(kernel complains about irq 10 being the registered irq
> handler) though it causes other kernel problems. The following options
> have been tried in isolation with no success: pci=nommconf; pci=conf2
> (noboot); acpi=bigsmp; pci=routeirq (kernel output changes, but no
> change in behavior); pci=noacpi acpi=noirq (seems identical to
> pci=routeirq); acpi=irq_balance; apic=debug.
> 
> I'm running primarily in a Dell precision 370n workstation with 3
> PCI-X slots. The irq reported in by the IO-APIC changes depending on
> which slot I plug it in.
> 
> Slot       INTERRUPT_LINE     IO-APIC        Observed
> 1           10                            49                 17
> 2           10                            53                 17
> 3           9                              26                 18
> 
> The same general behavior has been observed in _every_ linux machine
> I've been able to plug this card into that had an IO-APIC. These were
> mostly Intel chipsets but I 've also had it in a Tyan 8-proc AMD board
> with a Nvidia chipset with the same interrupt issues.
> 
> I see two problems: first, the INTERRUPT_LINE register on the card is
> not consistent with either the APIC reported irq or the actual irq.
> Second, that the IO_APIC, which is supposed to maintain a mapping of
> its pins to a particular irq, is inconsistent in what IRQ is reported
> for a particular pin (different slots result in different irqs
> reported, but still actually use irq 17).
> 
> I'm not a LKML subscriber so please CC to brett.boren_at_gmail_dot_com.

You should only be using the interrupt which is listed in the irq member 
of the struct pci_dev for your device. Likely if you do that your 
problems will go away.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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