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Commit 4ab6a219 authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Ingo Molnar
Browse files

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: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent dfdf748a

drivers/clocksource/acpi_pm.c

+29 −17
Original line number Diff line number Diff line
@@ -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: */

	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)

			goto pm_good;

				good++;

				break;

			if ((value2 < value1) && ((value2) < 0xFFF))

			goto pm_good;

				good++;

				break;

			printk(KERN_INFO "PM-Timer had inconsistent results:"

			" 0x%#llx, 0x%#llx - aborting.\n", value1, value2);

			       " 0x%#llx, 0x%#llx - aborting.\n",

			       value1, value2);

			return -EINVAL;

		}

	printk(KERN_INFO "PM-Timer had no reasonable result:"

			" 0x%#llx - aborting.\n", value1);

		udelay(300 * i);

	}



	if (good != ACPI_PM_MONOTONICITY_CHECKS) {

		printk(KERN_INFO "PM-Timer failed consistency check "

		       " (0x%#llx) - aborting.\n", value1);

		return -ENODEV;

	}



pm_good:

	if (verify_pmtmr_rate() != 0)

		return -ENODEV;