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    SubjectRE: int. assignment on SMP + ServerWorks chipset


    On Mon, 15 Jan 2001, Dunlap, Randy wrote:
    >
    > Thanks for looking into this. I'll be out of touch for
    > the rest of this week, but Petr (pem@informatics.muni.cz)
    > should be able to test patches that Ingo comes up with.
    >
    > > Ok. That means that the problem is that we _should_ look at
    > > the pirq table even if we use the IO-APIC.
    >
    > How do we know when to do this?

    It's kind of nasty. The IO-APIC detection will disable the pirq table
    stuff, see pci-irq.c:

    /* If we're using the I/O APIC, avoid using the PCI IRQ routing table */
    if (io_apic_assign_pci_irqs)
    pirq_table = NULL;

    now, you could just remove that logic, but I suspect that you'd get
    problems simply because the interrupt will then get routing information,
    but either the IO-APIC re-naming logic has already moved the irq and it
    will be routed to the wrong entry.

    So what I _think_ is the correct change is to do roughly this in
    arch/i386/kernel/pci-irq.c:

    - in pcibios_fixup_irqs(), remove the

    #idef CONFIG_X86_IO_APIC
    ...
    #endif

    section entirely.

    - in pcibios_enable_irq(), at the _end_ (after having enabled the irq
    with "pcibios_lookup_irq(dev, 1)", do something like

    irq = IO_APIC_get_PCI_irq_vector(dev->bus->number, PCI_SLOT(dev->devfn), pin);
    if (irq > 0)
    dev->irq = irq;

    and add a LOT of debug printk's, and enable DEBUG in pci-i386.h.

    It probably won't work on the first try (even if I explained the above
    well enough), so send me and Ingo dmesg output, and maybe we'll figure out
    something.

    And if anybody else understands pirq routing, speak up. It's a black art.

    Linus

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