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

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Message-ID: <50194115.2030307@linutronix.de>
Date:	Wed, 01 Aug 2012 16:45:41 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: x86 and I/O APIC IRQ domains

On 08/01/2012 03:58 PM, Thierry Reding wrote:
> 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.

The IOAPIC knows how many sources are available and this number should
be used instead of 32.
This won't solve the problem with get_irq_data() for the second ioapic
which might be available in the system.

The reason why there is no irq_data() available is that this is
allocated by io_apic_setup_irq_pin_once() which is now called too late. 
Usually a PCI device does a pci_enable() call and then we do all this.
So to keep the function happy you should preallocate all interrupts
which are offered. Ah, and you may need a map function which does
nothing because the programming is done at io_apic_setup_irq_pin_once()
time.
Maybe you could live with irq_domain_add_linear() instead. Not sure how
important it is to keep rtc at a fixed irq. I think as far as the
IOAPIC is concerned, it could be programmed to another number but I
kept it in sync. However parts of the ioapic code rely on gsi_number ==
irq number so maybe we should preallocate the irq_data and use a dummy
map() function for the start.

> 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.
Currently it does not

> 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?

There is an option which delays each printk by a few msecs. Maybe this
could help.

>
> Thierry

Sebastian
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