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x86: hpet: Make WARN_ON understandable

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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>
This commit is contained in:
Thomas Gleixner 2009-11-27 15:24:44 +01:00
parent c8bc6f3c80
commit 18ed61da98
1 changed files with 15 additions and 4 deletions
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19
arch/x86/kernel/hpet.c
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@ -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;
}