aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/kernel/tsc.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c234
1 files changed, 185 insertions, 49 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 8e786b0d665..8f98e9de1b8 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -122,80 +122,216 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet)
return ULLONG_MAX;
}
-/**
- * native_calibrate_tsc - calibrate the tsc on boot
+/*
+ * 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.
*/
-unsigned long native_calibrate_tsc(void)
+static unsigned long pit_calibrate_tsc(void)
{
- unsigned long flags;
- u64 tsc1, tsc2, tr1, tr2, delta, pm1, pm2, hpet1, hpet2;
- int hpet = is_hpet_enabled();
- unsigned int tsc_khz_val = 0;
-
- local_irq_save(flags);
-
- tsc1 = tsc_read_refs(&pm1, hpet ? &hpet1 : NULL);
+ 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);
- tr1 = get_cycles();
- while ((inb(0x61) & 0x20) == 0);
- tr2 = get_cycles();
- tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);
+ tsc = t1 = t2 = get_cycles();
- local_irq_restore(flags);
+ 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++;
+ }
/*
- * Preset the result with the raw and inaccurate PIT
- * calibration value
+ * 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.
*/
- delta = (tr2 - tr1);
+ if (pitcnt < 5000 || tscmax > 10 * tscmin)
+ return ULONG_MAX;
+
+ /* Calculate the PIT value */
+ delta = t2 - t1;
do_div(delta, 50);
- tsc_khz_val = delta;
+ return delta;
+}
+
+
+/**
+ * native_calibrate_tsc - calibrate the tsc on boot
+ */
+unsigned long native_calibrate_tsc(void)
+{
+ u64 tsc1, tsc2, delta, pm1, pm2, hpet1, hpet2;
+ unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;
+ unsigned long flags;
+ int hpet = is_hpet_enabled(), i;
- /* hpet or pmtimer available ? */
+ /*
+ * Run 5 calibration loops to get the lowest frequency value
+ * (the best estimate). We use two different calibration modes
+ * here:
+ *
+ * 1) PIT loop. We set the PIT Channel 2 to oneshot mode and
+ * load a timeout of 50ms. We read the time right after we
+ * started the timer and wait until the PIT count down reaches
+ * zero. In each wait loop iteration we read the TSC and check
+ * the delta to the previous read. We keep track of the min
+ * and max values of that delta. The delta is mostly defined
+ * by the IO time of the PIT access, so we can detect when a
+ * SMI/SMM disturbance happend between the two reads. If the
+ * maximum time is significantly larger than the minimum time,
+ * then we discard the result and have another try.
+ *
+ * 2) Reference counter. If available we use the HPET or the
+ * PMTIMER as a reference to check the sanity of that value.
+ * We use separate TSC readouts and check inside of the
+ * reference read for a SMI/SMM disturbance. We dicard
+ * disturbed values here as well. We do that around the PIT
+ * calibration delay loop as we have to wait for a certain
+ * amount of time anyway.
+ */
+ for (i = 0; i < 5; i++) {
+ unsigned long tsc_pit_khz;
+
+ /*
+ * Read the start value and the reference count of
+ * 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);
+ tsc_pit_khz = pit_calibrate_tsc();
+ tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);
+ local_irq_restore(flags);
+
+ /* 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)
+ continue;
+
+ /* Check, whether the sampling was disturbed by an SMI */
+ if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX)
+ continue;
+
+ tsc2 = (tsc2 - tsc1) * 1000000LL;
+
+ if (hpet) {
+ if (hpet2 < hpet1)
+ hpet2 += 0x100000000ULL;
+ hpet2 -= hpet1;
+ tsc1 = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
+ do_div(tsc1, 1000000);
+ } else {
+ if (pm2 < pm1)
+ pm2 += (u64)ACPI_PM_OVRRUN;
+ pm2 -= pm1;
+ tsc1 = pm2 * 1000000000LL;
+ do_div(tsc1, PMTMR_TICKS_PER_SEC);
+ }
+
+ do_div(tsc2, tsc1);
+ tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2);
+ }
+
+ /*
+ * Now check the results.
+ */
+ if (tsc_pit_min == ULONG_MAX) {
+ /* PIT gave no useful value */
+ printk(KERN_WARNING "TSC: Unable to calibrate against PIT\n");
+
+ /* We don't have an alternative source, disable TSC */
+ if (!hpet && !pm1 && !pm2) {
+ printk("TSC: No reference (HPET/PMTIMER) available\n");
+ return 0;
+ }
+
+ /* The alternative source failed as well, disable TSC */
+ if (tsc_ref_min == ULONG_MAX) {
+ printk(KERN_WARNING "TSC: HPET/PMTIMER calibration "
+ "failed due to SMI disturbance.\n");
+ return 0;
+ }
+
+ /* Use the alternative source */
+ printk(KERN_INFO "TSC: using %s reference calibration\n",
+ hpet ? "HPET" : "PMTIMER");
+
+ return tsc_ref_min;
+ }
+
+ /* We don't have an alternative source, use the PIT calibration value */
if (!hpet && !pm1 && !pm2) {
- printk(KERN_INFO "TSC calibrated against PIT\n");
- goto out;
+ printk(KERN_INFO "TSC: Using PIT calibration value\n");
+ return tsc_pit_min;
}
- /* Check, whether the sampling was disturbed by an SMI */
- if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX) {
- printk(KERN_WARNING "TSC calibration disturbed by SMI, "
- "using PIT calibration result\n");
- goto out;
+ /* The alternative source failed, use the PIT calibration value */
+ if (tsc_ref_min == ULONG_MAX) {
+ printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed due "
+ "to SMI disturbance. Using PIT calibration\n");
+ return tsc_pit_min;
}
- tsc2 = (tsc2 - tsc1) * 1000000LL;
-
- if (hpet) {
- printk(KERN_INFO "TSC calibrated against HPET\n");
- if (hpet2 < hpet1)
- hpet2 += 0x100000000ULL;
- hpet2 -= hpet1;
- tsc1 = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
- do_div(tsc1, 1000000);
- } else {
- printk(KERN_INFO "TSC calibrated against PM_TIMER\n");
- if (pm2 < pm1)
- pm2 += (u64)ACPI_PM_OVRRUN;
- pm2 -= pm1;
- tsc1 = pm2 * 1000000000LL;
- do_div(tsc1, PMTMR_TICKS_PER_SEC);
+ /* Check the reference deviation */
+ delta = ((u64) tsc_pit_min) * 100;
+ do_div(delta, tsc_ref_min);
+
+ /*
+ * If both calibration results are inside a 5% window, the we
+ * use the lower frequency of those as it is probably the
+ * closest estimate.
+ */
+ if (delta >= 95 && delta <= 105) {
+ printk(KERN_INFO "TSC: PIT calibration confirmed by %s.\n",
+ hpet ? "HPET" : "PMTIMER");
+ printk(KERN_INFO "TSC: using %s calibration value\n",
+ tsc_pit_min <= tsc_ref_min ? "PIT" :
+ hpet ? "HPET" : "PMTIMER");
+ return tsc_pit_min <= tsc_ref_min ? tsc_pit_min : tsc_ref_min;
}
- do_div(tsc2, tsc1);
- tsc_khz_val = tsc2;
+ printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n",
+ hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
-out:
- return tsc_khz_val;
+ /*
+ * The calibration values differ too much. In doubt, we use
+ * the PIT value as we know that there are PMTIMERs around
+ * running at double speed.
+ */
+ printk(KERN_INFO "TSC: Using PIT calibration value\n");
+ return tsc_pit_min;
}
-
#ifdef CONFIG_X86_32
/* Only called from the Powernow K7 cpu freq driver */
int recalibrate_cpu_khz(void)
generated by cgit v1.2.3 (git 2.25.1) at 2024-05-21 17:44:20 +0000