+static unsigned long __cpuinit calibrate_delay_converge(void)
+{
+ /* First stage - slowly accelerate to find initial bounds */
+ unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
+ int trials = 0, band = 0, trial_in_band = 0;
+
+ lpj = (1<<12);
+
+ /* wait for "start of" clock tick */
+ ticks = jiffies;
+ while (ticks == jiffies)
+ ; /* nothing */
+ /* Go .. */
+ ticks = jiffies;
+ do {
+ if (++trial_in_band == (1<<band)) {
+ ++band;
+ trial_in_band = 0;
+ }
+ __delay(lpj * band);
+ trials += band;
+ } while (ticks == jiffies);
+ /*
+ * We overshot, so retreat to a clear underestimate. Then estimate
+ * the largest likely undershoot. This defines our chop bounds.
+ */
+ trials -= band;
+ loopadd_base = lpj * band;
+ lpj_base = lpj * trials;
+
+recalibrate:
+ lpj = lpj_base;
+ loopadd = loopadd_base;
+
+ /*
+ * Do a binary approximation to get lpj set to
+ * equal one clock (up to LPS_PREC bits)
+ */
+ chop_limit = lpj >> LPS_PREC;
+ while (loopadd > chop_limit) {
+ lpj += loopadd;
+ ticks = jiffies;
+ while (ticks == jiffies)
+ ; /* nothing */
+ ticks = jiffies;
+ __delay(lpj);
+ if (jiffies != ticks) /* longer than 1 tick */
+ lpj -= loopadd;
+ loopadd >>= 1;
+ }
+ /*
+ * If we incremented every single time possible, presume we've
+ * massively underestimated initially, and retry with a higher
+ * start, and larger range. (Only seen on x86_64, due to SMIs)
+ */
+ if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
+ lpj_base = lpj;
+ loopadd_base <<= 2;
+ goto recalibrate;
+ }
+
+ return lpj;
+}
+