linux-kernel - [PATCH 2/2] acpi_pm.c: check for monotonicity

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Date:	Mon, 18 Aug 2008 22:11:15 +0200
From:	Dominik Brodowski <linux@...inikbrodowski.net>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Mohr <andi@...as.de>, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, johnstul@...ibm.com,
	hirofumi@...l.parknet.co.jp, alan@...rguk.ukuu.org.uk,
	arjan@...radead.org
Subject: [PATCH 2/2] acpi_pm.c: check for monotonicity

>From 13cc8b6ff0d8198102f60691c38c07151a693c7b Mon Sep 17 00:00:00 2001
From: Dominik Brodowski <linux@...inikbrodowski.net>
Date: Sun, 10 Aug 2008 21:34:54 +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@...ibm.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
---
 drivers/clocksource/acpi_pm.c |   42 ++++++++++++++++++++++++----------------
 1 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 2c00edd..f05c4fb 100644
--- a/drivers/clocksource/acpi_pm.c
+++ b/drivers/clocksource/acpi_pm.c
@@ -178,7 +178,7 @@ static int verify_pmtmr_rate(void)
 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 +187,32 @@ 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 < 10; 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 != 10) {
+		printk(KERN_INFO "PM-Timer had no reasonable result:"
+		       " 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;
 
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