Re: PROBLEM: do_IRQ: [number] No irq handler for vector (irq -1)

[Anthony DeRobertis <aderobertis-VnMYzjHJ8tfR7s880joybQ@public.gmane.org>]

I was looking through those files a bit, and notice there is a 
iommu_disable_irq_remapping. I added some printk's to it, and it isn't 
being called when the BIOS workaround is hit.

 From the code, I gather that it should be disabled at boot, and the 
disable_irq_remap flag works by just pretending its not supported, so it 
never gets enabled.

However, I see in the enable path (intel_enable_irq_remapping) there is 
this:

		/*
		 * Disable intr remapping and queued invalidation, if already
		 * enabled prior to OS handover.
		 */
		iommu_disable_irq_remapping(iommu);

It sounds like someone found a BIOS before that hands off to Linux with 
it already enabled.

So, I added a call to disable_irq_remapping, but it turns out that this 
BIOS doesn't do that. So doesn't help here.

Also, I notice that iommu_disable_irq_remapping looks suspicious as its 
weird that GSTS is being read with both readl and dmar_readq. I think 
readl is correct, as I think the Intel spec says its a 32-bit field.