x86/hpet: Use the FSEC_PER_SEC constant for femto-second periods

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 <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Acked-by: Ingo Molnar <[e-mail]>
Acked-by: H. Peter Anvin <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/x86/kernel/hpet.c

···
 	 * 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);
···
 	 * 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

···
 #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)