Split up PIT part of TSC calibration from native_calibrate_tsc

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>

1 files changed, 71 insertions, 61 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index ac79bd143da8..346cae5ac423 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)