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>

1 files changed, 29 insertions, 17 deletions

diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 860d033bc74f..4eee533f3f4a 100644
--- 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;