linux-kernel - x86 and I/O APIC IRQ domains

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Message-ID: <20120801135839.GA19957@avionic-0098.adnet.avionic-design.de>
Date:	Wed, 1 Aug 2012 15:58:39 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: x86 and I/O APIC IRQ domains

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.

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?

Thierry

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