Commit-ID: 04abd607d3fa65b7f3952e728c9b2f35d17e94a1 Gitweb: http://git.kernel.org/tip/04abd607d3fa65b7f3952e728c9b2f35d17e94a1 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Fri, 27 Nov 2009 15:24:44 +0100 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitDate: Fri, 27 Nov 2009 15:24:44 +0100 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@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Venki Pallipadi <venkatesh.pallipadi@xxxxxxxxx> --- arch/x86/kernel/hpet.c | 19 +++++++++++++++---- 1 files changed, 15 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index dedc2bd..991d57d 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -383,11 +383,22 @@ 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; } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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