linux-kernel - Re: [PATCH 3/3] x86: hpet: stop HPET_COUNTER when programming periodic mode

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Message-ID: <20090224062541.GO6298@alberich.amd.com>
Date:	Tue, 24 Feb 2009 07:25:41 +0100
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org, Mark Hounschell <markh@...pro.net>,
	Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 3/3] x86: hpet: stop HPET_COUNTER when programming
	periodic mode

On Sat, Feb 21, 2009 at 12:16:35AM +0100, Andreas Herrmann wrote:
> 
> Impact: fix system hang on some systems operating with HZ_1000
> 
> On a system that stalled with HZ_1000, the first value written to
> T0_CMP (when the main counter was not stopped) did not trigger an
> interrupt. Instead after the main counter wrapped around (after
> several minutes) an interrupt was triggered and afterwards the
> periodic interrupt took effect.
> 
> This can be fixed by implementing HPET spec recommendation for
> programming the periodic mode (i.e. stopping the main counter).

Hi Ingo,

Please don't push this commit to Linus' tree.
Currently it's in tip:timers/hpet.

The patch didn't fix the problem that Mark Hounshell was reporting.

But first of all the patch might have side-effects as all hpet timers
that are affect when the main counter is stopped and reset. And
furthermore I have learned that there might have been hpet
implementations that require the second write (w/o HPET_TN_SETVAL bit)
to happen.

I am looking for a different solution.


Thanks,

Andreas


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