diff options
Diffstat (limited to 'arch/x86/kernel/tsc.c')
| -rw-r--r-- | arch/x86/kernel/tsc.c | 135 |
1 files changed, 72 insertions, 63 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index ac79bd143da..8f98e9de1b8 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -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) @@ -257,8 +267,7 @@ unsigned long native_calibrate_tsc(void) */ if (tsc_pit_min == ULONG_MAX) { /* PIT gave no useful value */ - printk(KERN_WARNING "TSC: PIT calibration failed due to " - "SMI disturbance.\n"); + printk(KERN_WARNING "TSC: Unable to calibrate against PIT\n"); /* We don't have an alternative source, disable TSC */ if (!hpet && !pm1 && !pm2) { |