clocksource, acpi_pm.c: check for monotonicity

The current check for monotonicity is way too weak: Andreas Mohr reports (
http://lkml.org/lkml/2008/8/10/77 ) that on one of his test systems the
current check only triggers in 50% of all cases, leading to catastrophic
timer behaviour.  To fix this issue, expand the check for monotonicity by
doing ten consecutive tests instead of one.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 860d033..4eee533 100644 (file)
--- a/drivers/clocksource/acpi_pm.c
+++ b/drivers/clocksource/acpi_pm.c
@@ -21,6 +21,7 @@
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/pci.h>
+#include <linux/delay.h>
 #include <asm/io.h>
 
 /*
@@ -175,10 +176,13 @@ static int verify_pmtmr_rate(void)
 #define verify_pmtmr_rate() (0)
 #endif
 
+/* Number of monotonicity checks to perform during initialization */
+#define ACPI_PM_MONOTONICITY_CHECKS 10
+
 static int __init init_acpi_pm_clocksource(void)
 {
        cycle_t value1, value2;
-       unsigned int i;
+       unsigned int i, j, good = 0;
 
        if (!pmtmr_ioport)
                return -ENODEV;
@@ -187,24 +191,32 @@ static int __init init_acpi_pm_clocksource(void)
                                                clocksource_acpi_pm.shift);
 
        /* "verify" this timing source: */
-       value1 = clocksource_acpi_pm.read();
-       for (i = 0; i < 10000; i++) {
-               value2 = clocksource_acpi_pm.read();
-               if (value2 == value1)
-                       continue;
-               if (value2 > value1)
-                       goto pm_good;
-               if ((value2 < value1) && ((value2) < 0xFFF))
-                       goto pm_good;
-               printk(KERN_INFO "PM-Timer had inconsistent results:"
-                       " 0x%#llx, 0x%#llx - aborting.\n", value1, value2);
-               return -EINVAL;
+       for (j = 0; j < ACPI_PM_MONOTONICITY_CHECKS; j++) {
+               value1 = clocksource_acpi_pm.read();
+               for (i = 0; i < 10000; i++) {
+                       value2 = clocksource_acpi_pm.read();
+                       if (value2 == value1)
+                               continue;
+                       if (value2 > value1)
+                               good++;
+                               break;
+                       if ((value2 < value1) && ((value2) < 0xFFF))
+                               good++;
+                               break;
+                       printk(KERN_INFO "PM-Timer had inconsistent results:"
+                              " 0x%#llx, 0x%#llx - aborting.\n",
+                              value1, value2);
+                       return -EINVAL;
+               }
+               udelay(300 * i);
+       }
+
+       if (good != ACPI_PM_MONOTONICITY_CHECKS) {
+               printk(KERN_INFO "PM-Timer failed consistency check "
+                      " (0x%#llx) - aborting.\n", value1);
+               return -ENODEV;
        }
-       printk(KERN_INFO "PM-Timer had no reasonable result:"
-                       " 0x%#llx - aborting.\n", value1);
-       return -ENODEV;
 
-pm_good:
        if (verify_pmtmr_rate() != 0)
                return -ENODEV;