linux-kernel - Re: IRQ remapping problem on Macbook Air 5,1

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Message-ID: <20120807201030.GJ1917@8bytes.org>
Date:	Tue, 7 Aug 2012 22:10:30 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Seth Forshee <seth.forshee@...onical.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Len Brown <lenb@...nel.org>,
	Joerg Roedel <joerg.roedel@....com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: IRQ remapping problem on Macbook Air 5,1

Hi Seth,

On Tue, Aug 07, 2012 at 02:48:37PM -0500, Seth Forshee wrote:
> This machine has a bug in its ACPI tables that's causing it to fail to
> boot unless intremap=off is passed to the kernel. The MADT defines a
> single IOAPIC with id 2, but the remapping unit defined in DMAR matches
> id 0. Thus interrupt remapping fails, and the kernel panics with the
> message "timer doesn't work through Interrupt-remapped IO-APIC." If I
> force the use of the non-matching ir hardware for the IOAPIC everything
> seems to works fine. dmesg for the working boot is below.

There are AMD systems with similar problems. For example I had a system
with 2 IO-APICs but only one was described in the IOMMU ACPI table.

> I'm looking at how to make this machine able to boot by default. OS X
> obviously boots, and Windows presumably boots as well since Apple
> officially supports running Windows on its hardware.

These operating systems probably don't support interrupt remapping, or
the IOMMU at all.

> I've got a patch to leave IRQ remapping disabled whenever any IOAPIC
> does not have a matching ir hardware unit. This gets it to boot, but I
> thought I'd check and see whether anyone had any better ideas for how to
> fix this.

This is exactly how I fixed this issue on the AMD side too. Mind to
submit the patch?


Thanks,

	Joerg


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