x86: hpet: fix periodic mode programming on AMD 81xx

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(See http://bugzilla.kernel.org/show_bug.cgi?id=12961)

It partially reverts commit c23e253e67
(x86: hpet: stop HPET_COUNTER when programming periodic mode)

HPET on AMD 81xx chipset needs a second write (with HPET_TN_SETVAL
cleared) to T0_CMP register to set the period in periodic mode.

With this patch HPET_COUNTER is still stopped but not reset when HPET
is programmed in periodic mode. This should help to avoid races when
HPET is programmed in periodic mode and fixes a boot time hang that
I've observed on a machine when using 1000HZ.

[ Impact: fix boot time hang on machines with AMD 81xx chipset ]

Reported-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Tested-by: Jeff Mahoney <jeffm@suse.com>
LKML-Reference: <20090421180037.GA2763@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

...

This commit is contained in:

Andreas Herrmann 2009-04-21 20:00:37 +02:00 • committed by Ingo Molnar

parent 3568b71d46

commit 7a6f9cbb37

1 changed files with 17 additions and 1 deletions

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arch/x86/kernel/hpet.c

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