[patch 100/114] x86, hpet: fix for LS21 + HPET = boot hang

[Greg KH]

2.6.28-stable review patch.  If anyone has any objections, please let us know.

------------------

From: john stultz <johnstul@xxxxxxxxxx>

commit b13e24644c138d0ddbc451403c30a96b09bfd556 upstream.

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 b8ce33590687888ebb900d09557b8807c4539022, 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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/x86/kernel/hpet.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -267,6 +267,8 @@ static void hpet_set_mode(enum clock_eve
 		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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