1 files changed, 186 insertions, 49 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 8e786b0d665a..346cae5ac423 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -122,80 +122,217 @@ 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: PIT calibration failed due to "
+                       "SMI disturbance.\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)