[RFC 2/4] PM / devfreq: suspend subsystem on system suspend/hibernate

[Tobias Jakobi <tjakobi@math.uni-bielefeld.de>]

On the Exynos4412 SoC the DevFreq subsystem adjusts frequency
of the various internal busses and corresponding voltages.

E.g. the clock of the DMC (dynamic memory controller) bus
together with the voltage of the MIF regulator are controlled
by this.

If DMC activity is low and DevFreq has set a lower OPP, the
following can happen.

If the system is restarted or goes into a suspend/resume-cycle,
the first-stage (BL0) bootloader takes over, which also
initializes clocks to default values. Since the PMIC is an
external component and not part of the SoC, the BL0 doesn't
set any default voltages. Upon setting the default clocks
for the DMC bus, the BL0 hangs because the corresponding
voltage is too low.

To fix this, we make sure to only go into suspend with a 'safe'
DevFreq configuration.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
---
 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 5a94dfa..9cd7e06 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"
@@ -943,6 +944,7 @@ void dpm_resume(pm_message_t state)
 	dpm_show_time(starttime, state, NULL);
 
 	cpufreq_resume();
+	devfreq_resume();
 	trace_suspend_resume(TPS("dpm_resume"), state.event, false);
 }
 
@@ -1582,6 +1584,7 @@ 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);
-- 
2.7.3