1 files changed, 94 insertions, 0 deletions

diff --git a/init/calibrate.c b/init/calibrate.c
index c698e04a3dbe..d206c7548fe6 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -8,6 +8,8 @@
 #include <linux/delay.h>
 #include <linux/init.h>
 
+#include <asm/timex.h>
+
 static unsigned long preset_lpj;
 static int __init lpj_setup(char *str)
 {
@@ -17,6 +19,92 @@ static int __init lpj_setup(char *str)
 
 __setup("lpj=", lpj_setup);
 
+#ifdef ARCH_HAS_READ_CURRENT_TIMER
+
+/* This routine uses the read_current_timer() routine and gets the
+ * loops per jiffy directly, instead of guessing it using delay().
+ * Also, this code tries to handle non-maskable asynchronous events
+ * (like SMIs)
+ */
+#define DELAY_CALIBRATION_TICKS                 ((HZ < 100) ? 1 : (HZ/100))
+#define MAX_DIRECT_CALIBRATION_RETRIES          5
+
+static unsigned long __devinit calibrate_delay_direct(void)
+{
+        unsigned long pre_start, start, post_start;
+        unsigned long pre_end, end, post_end;
+        unsigned long start_jiffies;
+        unsigned long tsc_rate_min, tsc_rate_max;
+        unsigned long good_tsc_sum = 0;
+        unsigned long good_tsc_count = 0;
+        int i;
+
+        if (read_current_timer(&pre_start) < 0 )
+                return 0;
+
+        /*
+         * A simple loop like
+         *      while ( jiffies < start_jiffies+1)
+         *              start = read_current_timer();
+         * will not do. As we don't really know whether jiffy switch
+         * happened first or timer_value was read first. And some asynchronous
+         * event can happen between these two events introducing errors in lpj.
+         *
+         * So, we do
+         * 1. pre_start <- When we are sure that jiffy switch hasn't happened
+         * 2. check jiffy switch
+         * 3. start <- timer value before or after jiffy switch
+         * 4. post_start <- When we are sure that jiffy switch has happened
+         *
+         * Note, we don't know anything about order of 2 and 3.
+         * Now, by looking at post_start and pre_start difference, we can
+         * check whether any asynchronous event happened or not
+         */
+
+        for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
+                pre_start = 0;
+                read_current_timer(&start);
+                start_jiffies = jiffies;
+                while (jiffies <= (start_jiffies + 1)) {
+                        pre_start = start;
+                        read_current_timer(&start);
+                }
+                read_current_timer(&post_start);
+
+                pre_end = 0;
+                end = post_start;
+                while (jiffies <=
+                       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
+                        pre_end = end;
+                        read_current_timer(&end);
+                }
+                read_current_timer(&post_end);
+
+                tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
+                tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
+
+                /*
+                 * If the upper limit and lower limit of the tsc_rate is
+                 * >= 12.5% apart, redo calibration.
+                 */
+                if (pre_start != 0 && pre_end != 0 &&
+                    (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
+                        good_tsc_count++;
+                        good_tsc_sum += tsc_rate_max;
+                }
+        }
+
+        if (good_tsc_count)
+                return (good_tsc_sum/good_tsc_count);
+
+        printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
+               "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
+        return 0;
+}
+#else
+static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
+#endif
+
 /*
  * This is the number of bits of precision for the loops_per_jiffy.  Each
  * bit takes on average 1.5/HZ seconds.  This (like the original) is a little
@@ -35,6 +123,12 @@ void __devinit calibrate_delay(void)
                         "%lu.%02lu BogoMIPS preset\n",
                         loops_per_jiffy/(500000/HZ),
                         (loops_per_jiffy/(5000/HZ)) % 100);
+        } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
+                printk("Calibrating delay using timer specific routine.. ");
+                printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
+                        loops_per_jiffy/(500000/HZ),
+                        (loops_per_jiffy/(5000/HZ)) % 100,
+                        loops_per_jiffy);
         } else {
                 loops_per_jiffy = (1<<12);