Initial import of modified Linux 2.6.28 tree

Original upstream URL:
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git | branch linux-2.6.28.y

1 files changed, 176 insertions, 0 deletions

diff --git a/init/calibrate.c b/init/calibrate.c
new file mode 100644
index 0000000..a379c90
--- /dev/null
+++ b/init/calibrate.c
@@ -0,0 +1,176 @@
+/* calibrate.c: default delay calibration
+ *
+ * Excised from init/main.c
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ */
+
+#include <linux/jiffies.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/timex.h>
+#include <linux/smp.h>
+
+unsigned long lpj_fine;
+unsigned long preset_lpj;
+static int __init lpj_setup(char *str)
+{
+	preset_lpj = simple_strtoul(str,NULL,0);
+	return 1;
+}
+
+__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 __cpuinit calibrate_delay_direct(void)
+{
+	unsigned long pre_start, start, post_start;
+	unsigned long pre_end, end, post_end;
+	unsigned long start_jiffies;
+	unsigned long timer_rate_min, timer_rate_max;
+	unsigned long good_timer_sum = 0;
+	unsigned long good_timer_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);
+
+		timer_rate_max = (post_end - pre_start) /
+					DELAY_CALIBRATION_TICKS;
+		timer_rate_min = (pre_end - post_start) /
+					DELAY_CALIBRATION_TICKS;
+
+		/*
+		 * If the upper limit and lower limit of the timer_rate is
+		 * >= 12.5% apart, redo calibration.
+		 */
+		if (pre_start != 0 && pre_end != 0 &&
+		    (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
+			good_timer_count++;
+			good_timer_sum += timer_rate_max;
+		}
+	}
+
+	if (good_timer_count)
+		return (good_timer_sum/good_timer_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 __cpuinit 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
+ * better than 1%
+ * For the boot cpu we can skip the delay calibration and assign it a value
+ * calculated based on the timer frequency.
+ * For the rest of the CPUs we cannot assume that the timer frequency is same as
+ * the cpu frequency, hence do the calibration for those.
+ */
+#define LPS_PREC 8
+
+void __cpuinit calibrate_delay(void)
+{
+	unsigned long ticks, loopbit;
+	int lps_precision = LPS_PREC;
+
+	if (preset_lpj) {
+		loops_per_jiffy = preset_lpj;
+		printk(KERN_INFO
+			"Calibrating delay loop (skipped) preset value.. ");
+	} else if ((smp_processor_id() == 0) && lpj_fine) {
+		loops_per_jiffy = lpj_fine;
+		printk(KERN_INFO
+			"Calibrating delay loop (skipped), "
+			"value calculated using timer frequency.. ");
+	} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
+		printk(KERN_INFO
+			"Calibrating delay using timer specific routine.. ");
+	} else {
+		loops_per_jiffy = (1<<12);
+
+		printk(KERN_INFO "Calibrating delay loop... ");
+		while ((loops_per_jiffy <<= 1) != 0) {
+			/* wait for "start of" clock tick */
+			ticks = jiffies;
+			while (ticks == jiffies)
+				/* nothing */;
+			/* Go .. */
+			ticks = jiffies;
+			__delay(loops_per_jiffy);
+			ticks = jiffies - ticks;
+			if (ticks)
+				break;
+		}
+
+		/*
+		 * Do a binary approximation to get loops_per_jiffy set to
+		 * equal one clock (up to lps_precision bits)
+		 */
+		loops_per_jiffy >>= 1;
+		loopbit = loops_per_jiffy;
+		while (lps_precision-- && (loopbit >>= 1)) {
+			loops_per_jiffy |= loopbit;
+			ticks = jiffies;
+			while (ticks == jiffies)
+				/* nothing */;
+			ticks = jiffies;
+			__delay(loops_per_jiffy);
+			if (jiffies != ticks)	/* longer than 1 tick */
+				loops_per_jiffy &= ~loopbit;
+		}
+	}
+	printk(KERN_CONT "%lu.%02lu BogoMIPS (lpj=%lu)\n",
+			loops_per_jiffy/(500000/HZ),
+			(loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
+}