RE: hangs in verify_pmtmr_rate()

[Yu, Fenghua]

> From: Dave Hansen [mailto:dave@xxxxxxxx]
> Sent: Wednesday, June 03, 2015 12:55 PM
> To: LKML; Yu, Fenghua; John Stultz; the arch/x86 maintainers
> 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?

Latest 4.1.0-rc5 defconfig boots fine without "pmtmr=0" on my machine which is same kind as Dave's.

I always give "hpet=disable" on this machine to w/a a known hw issue.

Thanks.

-Fenghua