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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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