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Commit 4936a3b9 authored by Chris Wilson's avatar Chris Wilson Committed by Linus Torvalds
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x86/hpet: Use the FSEC_PER_SEC constant for femto-second periods 



The current computation, introduced with f12a15be, 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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Acked-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent deda2e81

arch/x86/kernel/hpet.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

include/linux/time.h

+1 −1
Original line number Diff line number Diff line
@@ -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)