Devfreq framework supports suspend of its devices.
Call the the devfreq interface and allow devfreq devices preserve/restore
their states during suspend/resume.

The patch draws on Tobias Jakobi's work posted ~2 years ago, who tried to
solve issue with devfreq device's frequency during suspend/resume.
During the discussion on LKML some corner cases and comments appeared
related to the design. This patch address them keeping in mind suggestions
from Chanwoo Choi.

Suggested-by: Tobias Jakobi <redacted>
Signed-off-by: Lukasz Luba <redacted>
---
 drivers/base/power/main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index a690fd4..0992e67 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c

@@ -32,6 +32,7 @@
 #include <trace/events/power.h>
 #include <linux/cpufreq.h>
 #include <linux/cpuidle.h>
+#include <linux/devfreq.h>
 #include <linux/timer.h>
 
 #include "../base.h"

@@ -1078,6 +1079,7 @@ void dpm_resume(pm_message_t state)
 	dpm_show_time(starttime, state, 0, NULL);
 
 	cpufreq_resume();
+	devfreq_resume();
 	trace_suspend_resume(TPS("dpm_resume"), state.event, false);
 }
 

@@ -1852,6 +1854,7 @@ int dpm_suspend(pm_message_t state)
 	trace_suspend_resume(TPS("dpm_suspend"), state.event, true);
 	might_sleep();
 
+	devfreq_suspend();
 	cpufreq_suspend();
 
 	mutex_lock(&dpm_list_mtx);

-- 
2.7.4