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>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index ac79bd1..346cae5 100644 (file)
--- 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)