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Subject[PATCH 2/2] x86/hpet: Use the FSEC_PER_SEC constant for femto-second periods
Date
From: Chris Wilson <chris@chris-wilson.co.uk>

The current computation, introduced with f12a15be63, of FSEC_PER_SEC using
the multiplication of (FSEC_PER_NSEC * NSEC_PER_SEC) is performed only
with 32bit integers on small machines, resulting in an overflow and a
*very* short intervals being programmed. An interrupt storm follows.

Note that we also have to specify FSEC_PER_SEC as being long long to
overcome the same limitations.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/hpet.c | 4 ++--
include/linux/time.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 33dbcc4..351f9c0 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -582,7 +582,7 @@ static void init_one_hpet_msi_clockevent(struct hpet_dev *hdev, int cpu)
* scaled math multiplication factor for nanosecond to hpet tick
* conversion.
*/
- hpet_freq = 1000000000000000ULL;
+ hpet_freq = FSEC_PER_SEC;
do_div(hpet_freq, hpet_period);
evt->mult = div_sc((unsigned long) hpet_freq,
NSEC_PER_SEC, evt->shift);
@@ -837,7 +837,7 @@ static int hpet_clocksource_register(void)
* cyc/sec = FSEC_PER_SEC/hpet_period(fsec/cyc)
* cyc/sec = (FSEC_PER_NSEC * NSEC_PER_SEC)/hpet_period
*/
- hpet_freq = FSEC_PER_NSEC * NSEC_PER_SEC;
+ hpet_freq = FSEC_PER_SEC;
do_div(hpet_freq, hpet_period);
clocksource_register_hz(&clocksource_hpet, (u32)hpet_freq);

diff --git a/include/linux/time.h b/include/linux/time.h
index cb34e35..1261270 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -38,7 +38,7 @@ extern struct timezone sys_tz;
#define NSEC_PER_MSEC 1000000L
#define USEC_PER_SEC 1000000L
#define NSEC_PER_SEC 1000000000L
-#define FSEC_PER_SEC 1000000000000000L
+#define FSEC_PER_SEC 1000000000000000LL

#define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)

--
1.6.0.4


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