linux-kernel - Re: [PATCH] ACPI/hpet: prevent boot hang when hpet=force used on ICH-4M

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Date:	Fri, 24 Apr 2009 08:37:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Len Brown <lenb@...nel.org>
Cc:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] ACPI/hpet: prevent boot hang when hpet=force used on
	ICH-4M


* Len Brown <lenb@...nel.org> wrote:

> From: Len Brown <len.brown@...el.com>
> 
> Linux tells ICH4 users that they can (manually) invoke
> "hpet=force" to enable the undocumented ICH-4M HPET.
> The HPET becomes available for both clocksource and clockevents.
> 
> But as of ff69f2bba67bd45514923aaedbf40fe351787c59
> (acpi: fix of pmtimer overflow that make Cx states time incorrect)
> the HPET may be used via clocksource for idle accounting, and
> hpet=force on an ICH4 box hangs boot.
> 
> It turns out that touching the MMIO HPET withing
> the ARB_DIS part of C3 will hang the hardware.
> 
> The fix is to simply move the timer access outside
> the ARB_DIS region.  This is a no-op on modern hardware
> because ARB_DIS is no longer used.
> 
> http://bugzilla.kernel.org/show_bug.cgi?id=13087

Nice fix! This moots the other half-quirk patch you wrote for hpet, 
right?

	Ingo
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