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Commit cce3e057 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

x86: TSC: define the PIT latch value separate 



Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent d210baf5

arch/x86/kernel/tsc.c

+9 −5
Original line number Diff line number Diff line
@@ -122,6 +122,10 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet) 
	return ULLONG_MAX;

}



#define CAL_MS		50

#define CAL_LATCH	(CLOCK_TICK_RATE / (1000 / CAL_MS))

#define CAL_PIT_LOOPS	5000



/*

 * Try to calibrate the TSC against the Programmable

 * Interrupt Timer and return the frequency of the TSC
@@ -144,8 +148,8 @@ static unsigned long pit_calibrate_tsc(void) 
	 * (LSB then MSB) to begin countdown.

	 */

	outb(0xb0, 0x43);

	outb((CLOCK_TICK_RATE / (1000 / 50)) & 0xff, 0x42);

	outb((CLOCK_TICK_RATE / (1000 / 50)) >> 8, 0x42);

	outb(CAL_LATCH & 0xff, 0x42);

	outb(CAL_LATCH >> 8, 0x42);



	tsc = t1 = t2 = get_cycles();
@@ -166,18 +170,18 @@ static unsigned long pit_calibrate_tsc(void) 
	/*

	 * Sanity checks:

	 *

	 * If we were not able to read the PIT more than 5000

	 * If we were not able to read the PIT more than PIT_MIN_LOOPS

	 * times, then we have been hit by a massive SMI

	 *

	 * If the maximum is 10 times larger than the minimum,

	 * then we got hit by an SMI as well.

	 */

	if (pitcnt < 5000 || tscmax > 10 * tscmin)

	if (pitcnt < CAL_PIT_LOOPS || tscmax > 10 * tscmin)

		return ULONG_MAX;



	/* Calculate the PIT value */

	delta = t2 - t1;

	do_div(delta, 50);

	do_div(delta, CAL_MS);

	return delta;

}