From: Thomas Gleixner Date: Fri, 27 Nov 2009 14:24:44 +0000 (+0100) Subject: x86: hpet: Make WARN_ON understandable X-Git-Tag: firefly_0821_release~10186^2~1826 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0584aa8dea3dab7f49ce949f61d7ec92b6b29e3e;p=firefly-linux-kernel-4.4.55.git x86: hpet: Make WARN_ON understandable commit 18ed61da985c57eea3fe8038b13fa2837c9b3c3f upstream. 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 Signed-off-by: Thomas Gleixner Cc: Venki Pallipadi Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 58778736496a..4dda49c68a35 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -385,11 +385,22 @@ 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((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt); + WARN_ONCE((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt, + KERN_WARNING "hpet: compare register read back failed.\n"); return (s32)((u32)hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; }