PM: domains: use device's next wakeup to determine domain idle state

Currently, a PM domain's idle state is determined based on whether the
QoS requirements are met. However, even entering an idle state may waste
power if the minimum residency requirements aren't fulfilled.

CPU PM domains use the next timer wakeup for the CPUs in the domain to
determine the sleep duration of the domain. This is compared with the
idle state residencies to determine the optimal idle state. For other PM
domains, determining the sleep length is not that straight forward. But
if the device's next_event is available, we can use that to determine
the sleep duration of the PM domain.

Let's update the domain governor logic to check for idle state residency
based on the next wakeup of devices as well as QoS constraints. But
since, not all domains may contain devices capable of specifying the
next wakeup, let's enable this additional check only if specified by the
domain's flags when initializing the domain.

Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 93 insertions, 9 deletions

diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
index 490ed7deb99a..c6c218758f0b 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -117,6 +117,55 @@ static bool default_suspend_ok(struct device *dev)
 	return td->cached_suspend_ok;
 }
 
+static void update_domain_next_wakeup(struct generic_pm_domain *genpd, ktime_t now)
+{
+	ktime_t domain_wakeup = KTIME_MAX;
+	ktime_t next_wakeup;
+	struct pm_domain_data *pdd;
+	struct gpd_link *link;
+
+	if (!(genpd->flags & GENPD_FLAG_MIN_RESIDENCY))
+		return;
+
+	/*
+	 * Devices that have a predictable wakeup pattern, may specify
+	 * their next wakeup. Let's find the next wakeup from all the
+	 * devices attached to this domain and from all the sub-domains.
+	 * It is possible that component's a next wakeup may have become
+	 * stale when we read that here. We will ignore to ensure the domain
+	 * is able to enter its optimal idle state.
+	 */
+	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
+		next_wakeup = to_gpd_data(pdd)->next_wakeup;
+		if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
+			if (ktime_before(next_wakeup, domain_wakeup))
+				domain_wakeup = next_wakeup;
+	}
+
+	list_for_each_entry(link, &genpd->parent_links, parent_node) {
+		next_wakeup = link->child->next_wakeup;
+		if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
+			if (ktime_before(next_wakeup, domain_wakeup))
+				domain_wakeup = next_wakeup;
+	}
+
+	genpd->next_wakeup = domain_wakeup;
+}
+
+static bool next_wakeup_allows_state(struct generic_pm_domain *genpd,
+				     unsigned int state, ktime_t now)
+{
+	ktime_t domain_wakeup = genpd->next_wakeup;
+	s64 idle_time_ns, min_sleep_ns;
+
+	min_sleep_ns = genpd->states[state].power_off_latency_ns +
+		       genpd->states[state].residency_ns;
+
+	idle_time_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
+
+	return idle_time_ns >= min_sleep_ns;
+}
+
 static bool __default_power_down_ok(struct dev_pm_domain *pd,
 				     unsigned int state)
 {
@@ -201,16 +250,41 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
 }
 
 /**
- * default_power_down_ok - Default generic PM domain power off governor routine.
+ * _default_power_down_ok - Default generic PM domain power off governor routine.
  * @pd: PM domain to check.
  *
  * This routine must be executed under the PM domain's lock.
  */
-static bool default_power_down_ok(struct dev_pm_domain *pd)
+static bool _default_power_down_ok(struct dev_pm_domain *pd, ktime_t now)
 {
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
+	int state_idx = genpd->state_count - 1;
 	struct gpd_link *link;
 
+	/*
+	 * Find the next wakeup from devices that can determine their own wakeup
+	 * to find when the domain would wakeup and do it for every device down
+	 * the hierarchy. It is not worth while to sleep if the state's residency
+	 * cannot be met.
+	 */
+	update_domain_next_wakeup(genpd, now);
+	if ((genpd->flags & GENPD_FLAG_MIN_RESIDENCY) && (genpd->next_wakeup != KTIME_MAX)) {
+		/* Let's find out the deepest domain idle state, the devices prefer */
+		while (state_idx >= 0) {
+			if (next_wakeup_allows_state(genpd, state_idx, now)) {
+				genpd->max_off_time_changed = true;
+				break;
+			}
+			state_idx--;
+		}
+
+		if (state_idx < 0) {
+			state_idx = 0;
+			genpd->cached_power_down_ok = false;
+			goto done;
+		}
+	}
+
 	if (!genpd->max_off_time_changed) {
 		genpd->state_idx = genpd->cached_power_down_state_idx;
 		return genpd->cached_power_down_ok;
@@ -228,21 +302,30 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
 	genpd->max_off_time_ns = -1;
 	genpd->max_off_time_changed = false;
 	genpd->cached_power_down_ok = true;
-	genpd->state_idx = genpd->state_count - 1;
 
-	/* Find a state to power down to, starting from the deepest. */
-	while (!__default_power_down_ok(pd, genpd->state_idx)) {
-		if (genpd->state_idx == 0) {
+	/*
+	 * Find a state to power down to, starting from the state
+	 * determined by the next wakeup.
+	 */
+	while (!__default_power_down_ok(pd, state_idx)) {
+		if (state_idx == 0) {
 			genpd->cached_power_down_ok = false;
 			break;
 		}
-		genpd->state_idx--;
+		state_idx--;
 	}
 
+done:
+	genpd->state_idx = state_idx;
 	genpd->cached_power_down_state_idx = genpd->state_idx;
 	return genpd->cached_power_down_ok;
 }
 
+static bool default_power_down_ok(struct dev_pm_domain *pd)
+{
+	return _default_power_down_ok(pd, ktime_get());
+}
+
 static bool always_on_power_down_ok(struct dev_pm_domain *domain)
 {
 	return false;
@@ -254,11 +337,12 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
 	struct cpuidle_device *dev;
 	ktime_t domain_wakeup, next_hrtimer;
+	ktime_t now = ktime_get();
 	s64 idle_duration_ns;
 	int cpu, i;
 
 	/* Validate dev PM QoS constraints. */
-	if (!default_power_down_ok(pd))
+	if (!_default_power_down_ok(pd, now))
 		return false;
 
 	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN))
@@ -280,7 +364,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	}
 
 	/* The minimum idle duration is from now - until the next wakeup. */
-	idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, ktime_get()));
+	idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
 	if (idle_duration_ns <= 0)
 		return false;