From 18ed61da985c57eea3fe8038b13fa2837c9b3c3f Mon Sep 17 00:00:00 2001 From: Thomas Gleixner <tglx@linutronix.de> Date: Fri, 27 Nov 2009 15:24:44 +0100 Subject: [PATCH] x86: hpet: Make WARN_ON understandable Andrew complained rightly that the WARN_ON in hpet_next_event() is confusing and the code comment not really helpful. Change it to WARN_ONCE and print the reason in clear text. Change the comment to explain what kind of hardware wreckage we deal with. Pointed-out-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com> --- arch/x86/kernel/hpet.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 7f024ff47d1d..ba6e65884603 100644 --- a/arch/x86/kernel/hpet.c +++ b/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; } -- GitLab