[PATCH 2/4] cpu: expose pm_qos_resume_latency for each cpu

[Alex Shi]

Adding /sys/devices/system/cpu/cpux/power/pm_qos_resume_latency_us for
each of cpus. The pm_qos_resume_latency usage defined in
Documentation/ABI/testing/sysfs-devices-power

The cpu-dma PM QoS constraint impacts all the cpus in the system. There
is no way to let the user to choose a PM QoS constraint per cpu.

The following patch exposes to the userspace a per cpu based sysfs file
in order to let the userspace to change the value of the PM QoS latency
constraint.

This change is inoperative in its form and the cpuidle governors have to
take into account the per cpu latency constraint in addition to the
global cpu-dma latency constraint in order to operate properly.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx>
To: linux-kernel@xxxxxxxxxxxxxxx
To: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
 drivers/base/cpu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c28e1a..2c3b359 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -17,6 +17,7 @@
 #include <linux/of.h>
 #include <linux/cpufeature.h>
 #include <linux/tick.h>
+#include <linux/pm_qos.h>
 
 #include "base.h"
 
@@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
 
 	per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	register_cpu_under_node(num, cpu_to_node(num));
+	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
 
 	return 0;
 }
-- 
2.8.1.101.g72d917a