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Commit ec0c15af authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Split up PIT part of TSC calibration from native_calibrate_tsc 



The TSC calibration function is still very complicated, but this makes
it at least a little bit less so by moving the PIT part out into a
helper function of its own.

Tested-by: default avatarLarry Finger <Larry.Finger@lwfinger.net>
Signed-of-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d26acd92

arch/x86/kernel/tsc.c

+71 −61
Original line number Diff line number Diff line
@@ -122,15 +122,75 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet) 
	return ULLONG_MAX;

}



/*

 * Try to calibrate the TSC against the Programmable

 * Interrupt Timer and return the frequency of the TSC

 * in kHz.

 *

 * Return ULONG_MAX on failure to calibrate.

 */

static unsigned long pit_calibrate_tsc(void)

{

	u64 tsc, t1, t2, delta;

	unsigned long tscmin, tscmax;

	int pitcnt;



	/* Set the Gate high, disable speaker */

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);



	/*

	 * Setup CTC channel 2* for mode 0, (interrupt on terminal

	 * count mode), binary count. Set the latch register to 50ms

	 * (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);



	tsc = t1 = t2 = get_cycles();



	pitcnt = 0;

	tscmax = 0;

	tscmin = ULONG_MAX;

	while ((inb(0x61) & 0x20) == 0) {

		t2 = get_cycles();

		delta = t2 - tsc;

		tsc = t2;

		if ((unsigned long) delta < tscmin)

			tscmin = (unsigned int) delta;

		if ((unsigned long) delta > tscmax)

			tscmax = (unsigned int) delta;

		pitcnt++;

	}



	/*

	 * Sanity checks:

	 *

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

	 * 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)

		return ULONG_MAX;



	/* Calculate the PIT value */

	delta = t2 - t1;

	do_div(delta, 50);

	return delta;

}





/**

 * native_calibrate_tsc - calibrate the tsc on boot

 */

unsigned long native_calibrate_tsc(void)

{

	u64 tsc1, tsc2, tr1, tr2, tsc, delta, pm1, pm2, hpet1, hpet2;

	u64 tsc1, tsc2, delta, pm1, pm2, hpet1, hpet2;

	unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;

	unsigned long flags, tscmin, tscmax;

	int hpet = is_hpet_enabled(), pitcnt, i;

	unsigned long flags;

	int hpet = is_hpet_enabled(), i;



	/*

	 * Run 5 calibration loops to get the lowest frequency value
@@ -157,72 +217,22 @@ unsigned long native_calibrate_tsc(void) 
	 * amount of time anyway.

	 */

	for (i = 0; i < 5; i++) {



		tscmin = ULONG_MAX;

		tscmax = 0;

		pitcnt = 0;



		local_irq_save(flags);

		unsigned long tsc_pit_khz;



		/*

		 * Read the start value and the reference count of

		 * hpet/pmtimer when available:

		 * hpet/pmtimer when available. Then do the PIT

		 * calibration, which will take at least 50ms, and

		 * read the end value.

		 */

		local_irq_save(flags);

		tsc1 = tsc_read_refs(&pm1, hpet ? &hpet1 : NULL);



		/* Set the Gate high, disable speaker */

		outb((inb(0x61) & ~0x02) | 0x01, 0x61);



		/*

		 * Setup CTC channel 2* for mode 0, (interrupt on terminal

		 * count mode), binary count. Set the latch register to 50ms

		 * (LSB then MSB) to begin countdown.

		 *

		 * Some devices need a delay here.

		 */

		outb(0xb0, 0x43);

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

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



		tsc = tr1 = tr2 = get_cycles();



		while ((inb(0x61) & 0x20) == 0) {

			tr2 = get_cycles();

			delta = tr2 - tsc;

			tsc = tr2;

			if ((unsigned int) delta < tscmin)

				tscmin = (unsigned int) delta;

			if ((unsigned int) delta > tscmax)

				tscmax = (unsigned int) delta;

			pitcnt++;

		}



		/*

		 * We waited at least 50ms above. Now read

		 * pmtimer/hpet reference again

		 */

		tsc_pit_khz = pit_calibrate_tsc();

		tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);



		local_irq_restore(flags);



		/*

		 * Sanity checks:

		 *

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

		 * 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) {



			/* Calculate the PIT value */

			delta = tr2 - tr1;

			do_div(delta, 50);



			/* We take the smallest value into account */

			tsc_pit_min = min(tsc_pit_min, (unsigned long) delta);

		}

		/* Pick the lowest PIT TSC calibration so far */

		tsc_pit_min = min(tsc_pit_min, tsc_pit_khz);



		/* hpet or pmtimer available ? */

		if (!hpet && !pm1 && !pm2)