Commit b13e2464 authored Feb 12, 2009 by john stultz Committed by Ingo Molnar Feb 13, 2009

x86, hpet: fix for LS21 + HPET = boot hang



Between 2.6.23 and 2.6.24-rc1 a change was made that broke IBM LS21
systems that had the HPET enabled in the BIOS, resulting in boot hangs
for x86_64.

Specifically commit b8ce3359, which
merges the i386 and x86_64 HPET code.

Prior to this commit, when we setup the HPET timers in x86_64, we did
the following:

	hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
                    HPET_TN_32BIT, HPET_T0_CFG);

However after the i386/x86_64 HPET merge, we do the following:

	cfg = hpet_readl(HPET_Tn_CFG(timer));
	cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
			HPET_TN_SETVAL | HPET_TN_32BIT;
	hpet_writel(cfg, HPET_Tn_CFG(timer));

However on LS21s with HPET enabled in the BIOS, the HPET_T0_CFG register
boots with Level triggered interrupts (HPET_TN_LEVEL) enabled. This
causes the periodic interrupt to be not so periodic, and that results in
the boot time hang I reported earlier in the delay calibration.

My fix: Always disable HPET_TN_LEVEL when setting up periodic mode.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 7ad9de6a

arch/x86/kernel/hpet.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -269,6 +269,8 @@ static void hpet_set_mode(enum clock_event_mode mode,
		now = hpet_readl(HPET_COUNTER);
		cmp = now + (unsigned long) delta;
		cfg = hpet_readl(HPET_Tn_CFG(timer));
		/* Make sure we use edge triggered interrupts */
		cfg &= ~HPET_TN_LEVEL;
		cfg \|= HPET_TN_ENABLE \| HPET_TN_PERIODIC \|
		HPET_TN_SETVAL \| HPET_TN_32BIT;
		hpet_writel(cfg, HPET_Tn_CFG(timer));

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