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Subject[PATCH v2 2/2] acpi_pm.c: check for monotonicity


From: Dominik Brodowski <linux@dominikbrodowski.net>
Date: Fri, 22 Aug 2008 23:51:23 +0200
Subject: [PATCH 2/2] 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.

CC: John Stultz <johnstul@us.ibm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
drivers/clocksource/acpi_pm.c | 46 +++++++++++++++++++++++++---------------
1 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 860d033..4eee533 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;

--
1.5.2.5


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