[PATCH] time: re-add verify_pmtmr_rate

This patch re-adds the verify_pmtmr_rate functionality from 2.6.17 that
I dropped 2.6.18.

This resolves problems seen on older K6 ASUS boards where the ACPI PM
timer runs too fast.

See:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=211902
http://bugme.osdl.org/show_bug.cgi?id=2375

Thanks to Ian Campbell for re-reporting this and testing the fix!
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Ian Campbell <ijc@hellion.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/clocksource/acpi_pm.c

@@ -142,6 +142,39 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_SERVERWORKS, PCI_DEVICE_ID_SERVERWORKS_LE,
 			acpi_pm_check_graylist);
 #endif
 
+#ifndef CONFIG_X86_64
+#include "mach_timer.h"
+#define PMTMR_EXPECTED_RATE \
+  ((CALIBRATE_LATCH * (PMTMR_TICKS_PER_SEC >> 10)) / (CLOCK_TICK_RATE>>10))
+/*
+ * Some boards have the PMTMR running way too fast. We check
+ * the PMTMR rate against PIT channel 2 to catch these cases.
+ */
+static int verify_pmtmr_rate(void)
+{
+	u32 value1, value2;
+	unsigned long count, delta;
+
+	mach_prepare_counter();
+	value1 = read_pmtmr();
+	mach_countup(&count);
+	value2 = read_pmtmr();
+	delta = (value2 - value1) & ACPI_PM_MASK;
+
+	/* Check that the PMTMR delta is within 5% of what we expect */
+	if (delta < (PMTMR_EXPECTED_RATE * 19) / 20 ||
+	    delta > (PMTMR_EXPECTED_RATE * 21) / 20) {
+		printk(KERN_INFO "PM-Timer running at invalid rate: %lu%% "
+			"of normal - aborting.\n",
+			100UL * delta / PMTMR_EXPECTED_RATE);
+		return -1;
+	}
+
+	return 0;
+}
+#else
+#define verify_pmtmr_rate() (0)
+#endif
 
 static int __init init_acpi_pm_clocksource(void)
 {
@@ -173,6 +206,9 @@ static int __init init_acpi_pm_clocksource(void)
 	return -ENODEV;
 
 pm_good:
+	if (verify_pmtmr_rate() != 0)
+		return -ENODEV;
+
 	return clocksource_register(&clocksource_acpi_pm);
 }