linux-kernel - hangs in verify_pmtmr

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Date:	Wed, 03 Jun 2015 12:55:27 -0700
From:	Dave Hansen <dave@...1.net>
To:	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	John Stultz <john.stultz@...aro.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: hangs in verify_pmtmr_rate()

I'm seeing boot hangs when trying to boot a 32-bit 4.1.0-rc5 kernel on
some 64-bit CPUs (I'm not sure if it is a regression).  The NMI watchdog
shows init_acpi_pm_clocksource() as the last thing in the backtrace,
specifically verify_pmtmr_rate()'s I/O instructions.  It appears to be
mach_countup()'s while loop that gets stuck.

Booting with "pmtmr=0" works around this for me, as would unsetting
CONFIG_X86_PM_TIMER I'd imagine.

The hardware I'm doing this on is a bit wonky and I think the hpet is
broken on it.

Does this look like *really* broken hardware, or something that we
should be detecting and able to recover from?
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