Remove the spinlock in pm_qos_requirement by making target_value an atomic type.
This is necessary for real-time since pm_qos_requirement is called by idle and
cannot be allowed to sleep.
Signed-off-by: John Kacur <jkacur at gmail dot com>

Index: linux-2.6.26.3-rt3/kernel/pm_qos_params.c
===================================================================
--- linux-2.6.26.3-rt3.orig/kernel/pm_qos_params.c
+++ linux-2.6.26.3-rt3/kernel/pm_qos_params.c
@@ -42,7 +42,7 @@
 #include <linux/uaccess.h>
 
 /*
- * locking rule: all changes to target_value or requirements or notifiers lists
+ * locking rule: all changes to requirements or notifiers lists
  * or pm_qos_object list and pm_qos_objects need to happen with pm_qos_lock
  * held, taken with _irqsave.  One lock to rule them all
  */
@@ -65,7 +65,7 @@ struct pm_qos_object {
 	struct miscdevice pm_qos_power_miscdev;
 	char *name;
 	s32 default_value;
-	s32 target_value;
+	atomic_t target_value;
 	s32 (*comparitor)(s32, s32);
 };
 
@@ -76,7 +76,7 @@ static struct pm_qos_object cpu_dma_pm_q
 	.notifiers = &cpu_dma_lat_notifier,
 	.name = "cpu_dma_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = 2000 * USEC_PER_SEC,
+	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
 	.comparitor = min_compare
 };
 
@@ -86,7 +86,7 @@ static struct pm_qos_object network_lat_
 	.notifiers = &network_lat_notifier,
 	.name = "network_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = 2000 * USEC_PER_SEC,
+	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
 	.comparitor = min_compare
 };
 
@@ -98,7 +98,7 @@ static struct pm_qos_object network_thro
 	.notifiers = &network_throughput_notifier,
 	.name = "network_throughput",
 	.default_value = 0,
-	.target_value = 0,
+	.target_value = ATOMIC_INIT(0),
 	.comparitor = max_compare
 };
 
@@ -149,13 +149,14 @@ static void update_target(int target)
 		extreme_value = pm_qos_array[target]->comparitor(
 				extreme_value, node->value);
 	}
-	if (pm_qos_array[target]->target_value != extreme_value) {
+	spin_unlock_irqrestore(&pm_qos_lock, flags);
+
+	if (atomic_read(&pm_qos_array[target]->target_value) != extreme_value) {
 		call_notifier = 1;
-		pm_qos_array[target]->target_value = extreme_value;
+		atomic_set(&pm_qos_array[target]->target_value, extreme_value);
 		pr_debug(KERN_ERR "new target for qos %d is %d\n", target,
-			pm_qos_array[target]->target_value);
+			atomic_read(&pm_qos_array[target]->target_value));
 	}
-	spin_unlock_irqrestore(&pm_qos_lock, flags);
 
 	if (call_notifier)
 		blocking_notifier_call_chain(pm_qos_array[target]->notifiers,
@@ -193,11 +194,8 @@ static int find_pm_qos_object_by_minor(i
 int pm_qos_requirement(int pm_qos_class)
 {
 	int ret_val;
-	unsigned long flags;
 
-	spin_lock_irqsave(&pm_qos_lock, flags);
-	ret_val = pm_qos_array[pm_qos_class]->target_value;
-	spin_unlock_irqrestore(&pm_qos_lock, flags);
+	ret_val = atomic_read(&pm_qos_array[pm_qos_class]->target_value);
 
 	return ret_val;
 }