ARM: localtimer: clean up local timer on hot unplug

When a CPU is hot unplugged, the generic tick code cleans up the
clock event device, but fails to call down to the device's set_mode
function to actually shut the device down.

To work around this, we've historically had a local_timer_stop()
callback out of the hotplug code.  However, this adds needless
complexity when we have the clock event device itself available.

Explicitly call the clock event device's set_mode function with
CLOCK_EVT_MODE_UNUSED, so that the hardware can be cleanly shutdown
without any special external callbacks.  When/if the generic code
is fixed, percpu_timer_stop() can be killed off.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/smp.c

@@ -189,6 +189,8 @@ int __cpuinit __cpu_up(unsigned int cpu)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
+static void percpu_timer_stop(void);
+
 /*
  * __cpu_disable runs on the processor to be shutdown.
  */
@@ -216,7 +218,7 @@ int __cpu_disable(void)
 	/*
 	 * Stop the local timer for this CPU.
 	 */
-	local_timer_stop();
+	percpu_timer_stop();
 
 	/*
 	 * Flush user cache and TLB mappings, and then remove this CPU
@@ -539,6 +541,21 @@ void __cpuinit percpu_timer_setup(void)
 	local_timer_setup(evt);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * The generic clock events code purposely does not stop the local timer
+ * on CPU_DEAD/CPU_DEAD_FROZEN hotplug events, so we have to do it
+ * manually here.
+ */
+static void percpu_timer_stop(void)
+{
+	unsigned int cpu = smp_processor_id();
+	struct clock_event_device *evt = &per_cpu(percpu_clockevent, cpu);
+
+	evt->set_mode(CLOCK_EVT_MODE_UNUSED, evt);
+}
+#endif
+
 static DEFINE_SPINLOCK(stop_lock);
 
 /*