+ 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;
+
+ /*
+ * 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;
+ }