i386: HPET, check if the counter works

Some systems have a HPET which is not incrementing, which leads to a
complete hang.  Detect it during HPET setup.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/hpet.c

@@ -232,7 +232,8 @@ int __init hpet_enable(void)
 {
 	unsigned long id;
 	uint64_t hpet_freq;
-	u64 tmp;
+	u64 tmp, start, now;
+	cycle_t t1;
 
 	if (!is_hpet_capable())
 		return 0;
@@ -279,6 +280,27 @@ int __init hpet_enable(void)
 	/* Start the counter */
 	hpet_start_counter();
 
+	/* Verify whether hpet counter works */
+	t1 = read_hpet();
+	rdtscll(start);
+
+	/*
+	 * We don't know the TSC frequency yet, but waiting for
+	 * 200000 TSC cycles is safe:
+	 * 4 GHz == 50us
+	 * 1 GHz == 200us
+	 */
+	do {
+		rep_nop();
+		rdtscll(now);
+	} while ((now - start) < 200000UL);
+
+	if (t1 == read_hpet()) {
+		printk(KERN_WARNING
+		       "HPET counter not counting. HPET disabled\n");
+		goto out_nohpet;
+	}
+
 	/* Initialize and register HPET clocksource
 	 *
 	 * hpet period is in femto seconds per cycle