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    SubjectRe: x86 and I/O APIC IRQ domains
    On Wed, Aug 01, 2012 at 03:58:39PM +0200, Thierry Reding wrote:
    > Hi,
    > I've been working on an x86 platform and want to use DT. However I've
    > hit a snag when trying to instantiate the I/O APIC. I've been trying to
    > follow what the CE4100 does and most things seem to work fine but when
    > I add the DT node for the I/O APIC things start to fail. I've been able
    > to trace the issue to x86_add_irq_domains(), which in turn calls
    > ioapic_add_ofnode() from which irq_domain_add_legacy() is called.
    > The platform that I use hits the WARN_ON(!irq_data || irq_data->domain).
    > Looking further this seems to be caused by all irq_get_irq_data(irq)
    > returning NULL for irq >= 16. That in turn I think is due to
    > init_ISA_irqs() setting up only the first NR_IRQS_LEGACY interrupts.
    > However the call to irq_domain_add_legacy() wants 32 interrupts.

    So it turns out that this is not due to init_ISA_irqs(). However,
    increasing NR_IRQS_LEGACY to 32 allows the code to get past that.

    > This was introduced by commit b4e5185 "irq_domain/x86: Convert x86
    > (embedded) to use common irq_domain)". I wonder what I'm doing wrong. I
    > don't get how this is made to work on CE4100.
    > Later the code crashes, but I can't exactly pinpoint the location
    > because the oops doesn't fit on the screen. I don't have a serial port
    > that I can use instead, so is there anything else I can do to obtain a
    > complete backtrace?

    This crash is in irq_domain_add_legacy() which tries to call the IRQ
    domain's .map() function, which isn't implemented for the I/O APIC.
    Adding an empty function allows the system to boot without any
    noticeable errors.

    I need to read up on the whole I/O APIC stuff because this is not really
    a fix and I don't know any better. Also, the CE4100 should exhibit the
    same issue after the above-mentioned commit. Can somebody more
    knowledgeable shed some light on this?

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