[PATCH -mm] Fix faulty HPET clocksource usage (fix for bug #7062)

[john stultz <johnstul@us.ibm.com>]

Apparently some systems export valid HPET addresses, but hpet_enable()
fails. Then when the HPET clocksource starts up, it only checks for a
valid HPET address, and the result is a system where time does not
advance.

See http://bugme.osdl.org/show_bug.cgi?id=7062 for details.

This patch just makes sure we better check that the HPET is functional
before registering the HPET clocksource.

Signed-off-by: John Stultz <johnstul@us.ibm.com>

diff --git a/arch/i386/kernel/hpet.c b/arch/i386/kernel/hpet.c
index c6737c3..17647a5 100644
--- a/arch/i386/kernel/hpet.c
+++ b/arch/i386/kernel/hpet.c
@@ -35,7 +35,7 @@ static int __init init_hpet_clocksource(
 	void __iomem* hpet_base;
 	u64 tmp;
 
-	if (!hpet_address)
+	if (!is_hpet_enabled())
 		return -ENODEV;
 
 	/* calculate the hpet address: */