From a4b65d3b23141228521430e23fba283a161bf2fa Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 27 Nov 2009 15:24:44 +0100 Subject: [PATCH] --- yaml --- r: 173127 b: refs/heads/master c: 18ed61da985c57eea3fe8038b13fa2837c9b3c3f h: refs/heads/master i: 173125: d9380cd4015a8e17016d172bea184f4e05f644ae 173123: fc0d468551b501187277ba1bd95c1e548e964e10 173119: ec6fb4df3bc08e11b7f4285500b0886d14f644b7 v: v3 --- [refs] | 2 +- trunk/arch/x86/kernel/hpet.c | 19 +++++++++++++++---- 2 files changed, 16 insertions(+), 5 deletions(-) diff --git a/[refs] b/[refs] index ab7e6700ae1d..39b0a4210c97 100644 --- a/[refs] +++ b/[refs] @@ -1,2 +1,2 @@ --- -refs/heads/master: c8bc6f3c806f1fcbfdbf0b1ff6c52dba59192d3b +refs/heads/master: 18ed61da985c57eea3fe8038b13fa2837c9b3c3f diff --git a/trunk/arch/x86/kernel/hpet.c b/trunk/arch/x86/kernel/hpet.c index 7f024ff47d1d..ba6e65884603 100644 --- a/trunk/arch/x86/kernel/hpet.c +++ b/trunk/arch/x86/kernel/hpet.c @@ -384,11 +384,22 @@ static int hpet_next_event(unsigned long delta, hpet_writel(cnt, HPET_Tn_CMP(timer)); /* - * We need to read back the CMP register to make sure that - * what we wrote hit the chip before we compare it to the - * counter. + * We need to read back the CMP register on certain HPET + * implementations (ATI chipsets) which seem to delay the + * transfer of the compare register into the internal compare + * logic. With small deltas this might actually be too late as + * the counter could already be higher than the compare value + * at that point and we would wait for the next hpet interrupt + * forever. We found out that reading the CMP register back + * forces the transfer so we can rely on the comparison with + * the counter register below. If the read back from the + * compare register does not match the value we programmed + * then we might have a real hardware problem. We can not do + * much about it here, but at least alert the user/admin with + * a prominent warning. */ - WARN_ON_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt); + WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt, + KERN_WARNING "hpet: compare register read back failed.\n"); return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; }