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Subject[090/197] x86: hpet: Make WARN_ON understandable
2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

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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