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Split up PIT part of TSC calibration from native_calibrate_tsc

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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: Larry Finger <Larry.Finger@lwfinger.net>
Signed-of-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2008-09-03 07:30:13 -07:00
parent d26acd92fa
commit ec0c15afb4
1 changed files with 71 additions and 61 deletions
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132
arch/x86/kernel/tsc.c
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@ -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)