| Date | Thu, 22 Apr 2010 12:09:01 -0700 | From | Greg KH <> | Subject | [090/197] x86: hpet: Make WARN_ON understandable |
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2.6.32-stable review patch. If anyone has any objections, please let us know.
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From: Thomas Gleixner <tglx@linutronix.de>
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 <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- arch/x86/kernel/hpet.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
--- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -385,11 +385,22 @@ static int hpet_next_event(unsigned long 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; }
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