x86: GEODE: make sure the right MFGPT timer fired the timer tick

Each AMD Geode MFGPT timer interrupt output is paired with another
timer; esentially the interrupt goes if either timer fires.  This
is okay, but the handlers need to be aware of this.  Make sure in
the timer tick handler that our timer really did expire.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/mfgpt_32.c

@@ -293,10 +293,14 @@ static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
 	return 0;
 }
 
-/* Assume (foolishly?), that this interrupt was due to our tick */
-
 static irqreturn_t mfgpt_tick(int irq, void *dev_id)
 {
+	u16 val = geode_mfgpt_read(mfgpt_event_clock, MFGPT_REG_SETUP);
+
+	/* See if the interrupt was for us */
+	if (!(val & (MFGPT_SETUP_SETUP  | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
+		return IRQ_NONE;
+
 	/* Turn off the clock (and clear the event) */
 	mfgpt_disable_timer(mfgpt_event_clock);