From b13e24644c138d0ddbc451403c30a96b09bfd556 Mon Sep 17 00:00:00 2001 From: john stultz Date: Thu, 12 Feb 2009 18:48:53 -0800 Subject: [PATCH] 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 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 Signed-off-by: Ingo Molnar --- arch/x86/kernel/hpet.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 64d5ad0b8add..5c8da2c2c185 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -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)); -- 2.30.2