[PATCH] cpuidle/menu: skip lock in per cpu resume latency reading

[Alex Shi]

dev_pm_qos_read_value using a lock to proctect the concurrent device
latency reading, that is useful for multiple cpu access a global device.
But it's not necessary for a per cpu data reading here. And furthermore,
RT kernel using mutex to replace spinlock causes fake panic here.

So, skip the lock using is nice for this per cpu value reading.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx>
---
 drivers/cpuidle/governors/menu.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 8d6d25c..b852d99 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -273,6 +273,14 @@ static unsigned int get_typical_interval(struct menu_device *data)
 	goto again;
 }
 
+int read_per_cpu_resume_latency(int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+
+	return IS_ERR_OR_NULL(dev->power.qos) ?
+		0 : pm_qos_read_value(&dev->power.qos->resume_latency);
+}
+
 /**
  * menu_select - selects the next idle state to enter
  * @drv: cpuidle driver containing state data
@@ -281,13 +289,12 @@ static unsigned int get_typical_interval(struct menu_device *data)
 static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = this_cpu_ptr(&menu_devices);
-	struct device *device = get_cpu_device(dev->cpu);
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 	unsigned int interactivity_req;
 	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
-	int resume_latency = dev_pm_qos_read_value(device);
+	int resume_latency = read_per_cpu_resume_latency(dev->cpu);
 
 	if (data->needs_update) {
 		menu_update(drv, dev);
-- 
2.8.1.101.g72d917a