[PATCH 2/3] PM: domains: Drop/restore performance state votes for devices at runtime PM

[Ulf Hansson]

A subsystem/driver that need to manage OPPs for its device, should
typically drop its vote for the OPP when the device becomes runtime
suspended. In this way, the corresponding aggregation of the performance
state votes that is managed in genpd for the attached PM domain, may find
that the aggregated vote can be decreased. Hence, it may allow genpd to set
the lower performance state for the PM domain, thus avoiding to waste
energy.

To accomplish this, typically a subsystem/driver would need to call
dev_pm_opp_set_rate|opp() for its device from its ->runtime_suspend()
callback, to drop the vote for the OPP. Accordingly, it needs another call
to dev_pm_opp_set_rate|opp() to restore the vote for the OPP from its
->runtime_resume() callback.

To avoid boilerplate code in subsystems/driver to deal with these things,
let's instead manage this internally in genpd.

Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
---
 drivers/base/power/domain.c | 21 +++++++++++++++++++--
 include/linux/pm_domain.h   |  1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index a3b6e751f366..81b9d4652b90 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -397,6 +397,18 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
 	return ret;
 }
 
+static int genpd_drop_performance_state(struct device *dev)
+{
+	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
+	unsigned int prev_state;
+
+	prev_state = gpd_data->performance_state;
+	if (prev_state && !genpd_set_performance_state(dev, 0))
+		return prev_state;
+
+	return 0;
+}
+
 /**
  * dev_pm_genpd_set_performance_state- Set performance state of device's power
  * domain.
@@ -839,7 +851,8 @@ static int genpd_runtime_suspend(struct device *dev)
 {
 	struct generic_pm_domain *genpd;
 	bool (*suspend_ok)(struct device *__dev);
-	struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
+	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
+	struct gpd_timing_data *td = &gpd_data->td;
 	bool runtime_pm = pm_runtime_enabled(dev);
 	ktime_t time_start;
 	s64 elapsed_ns;
@@ -896,6 +909,7 @@ static int genpd_runtime_suspend(struct device *dev)
 		return 0;
 
 	genpd_lock(genpd);
+	gpd_data->rpm_saved_pstate = genpd_drop_performance_state(dev);
 	genpd_power_off(genpd, true, 0);
 	genpd_unlock(genpd);
 
@@ -913,7 +927,8 @@ static int genpd_runtime_suspend(struct device *dev)
 static int genpd_runtime_resume(struct device *dev)
 {
 	struct generic_pm_domain *genpd;
-	struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
+	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
+	struct gpd_timing_data *td = &gpd_data->td;
 	bool runtime_pm = pm_runtime_enabled(dev);
 	ktime_t time_start;
 	s64 elapsed_ns;
@@ -937,6 +952,8 @@ static int genpd_runtime_resume(struct device *dev)
 
 	genpd_lock(genpd);
 	ret = genpd_power_on(genpd, 0);
+	if (!ret && gpd_data->rpm_saved_pstate)
+		genpd_set_performance_state(dev, gpd_data->rpm_saved_pstate);
 	genpd_unlock(genpd);
 
 	if (ret)
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index dfcfbcecc34b..c3d6c15788a3 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -198,6 +198,7 @@ struct generic_pm_domain_data {
 	struct notifier_block *power_nb;
 	int cpu;
 	unsigned int performance_state;
+	unsigned int rpm_saved_pstate;
 	ktime_t	next_wakeup;
 	void *data;
 };
-- 
2.25.1