1 files changed, 49 insertions, 37 deletions

diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
index 51751cc8c9e6..99896fbf18e4 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -14,20 +14,29 @@
 static int dev_update_qos_constraint(struct device *dev, void *data)
 {
 	s64 *constraint_ns_p = data;
-	s64 constraint_ns = -1;
+	s64 constraint_ns;
 
-	if (dev->power.subsys_data && dev->power.subsys_data->domain_data)
+	if (dev->power.subsys_data && dev->power.subsys_data->domain_data) {
+		/*
+		 * Only take suspend-time QoS constraints of devices into
+		 * account, because constraints updated after the device has
+		 * been suspended are not guaranteed to be taken into account
+		 * anyway.  In order for them to take effect, the device has to
+		 * be resumed and suspended again.
+		 */
 		constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
-
-	if (constraint_ns < 0)
+	} else {
+		/*
+		 * The child is not in a domain and there's no info on its
+		 * suspend/resume latencies, so assume them to be negligible and
+		 * take its current PM QoS constraint (that's the only thing
+		 * known at this point anyway).
+		 */
 		constraint_ns = dev_pm_qos_read_value(dev);
+		constraint_ns *= NSEC_PER_USEC;
+	}
 
-	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
-		return 0;
-
-	constraint_ns *= NSEC_PER_USEC;
-
-	if (constraint_ns < *constraint_ns_p || *constraint_ns_p < 0)
+	if (constraint_ns < *constraint_ns_p)
 		*constraint_ns_p = constraint_ns;
 
 	return 0;
@@ -55,7 +64,7 @@ static bool default_suspend_ok(struct device *dev)
 	}
 	td->constraint_changed = false;
 	td->cached_suspend_ok = false;
-	td->effective_constraint_ns = -1;
+	td->effective_constraint_ns = 0;
 	constraint_ns = __dev_pm_qos_read_value(dev);
 
 	spin_unlock_irqrestore(&dev->power.lock, flags);
@@ -63,11 +72,7 @@ static bool default_suspend_ok(struct device *dev)
 	if (constraint_ns == 0)
 		return false;
 
-	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
-		constraint_ns = -1;
-	else
-		constraint_ns *= NSEC_PER_USEC;
-
+	constraint_ns *= NSEC_PER_USEC;
 	/*
 	 * We can walk the children without any additional locking, because
 	 * they all have been suspended at this point and their
@@ -77,18 +82,31 @@ static bool default_suspend_ok(struct device *dev)
 		device_for_each_child(dev, &constraint_ns,
 				      dev_update_qos_constraint);
 
-	if (constraint_ns < 0) {
-		/* The children have no constraints. */
-		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS) {
+		/* "No restriction", so the device is allowed to suspend. */
+		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
 		td->cached_suspend_ok = true;
+	} else if (constraint_ns == 0) {
+		/*
+		 * This triggers if one of the children that don't belong to a
+		 * domain has a zero PM QoS constraint and it's better not to
+		 * suspend then.  effective_constraint_ns is zero already and
+		 * cached_suspend_ok is false, so bail out.
+		 */
+		return false;
 	} else {
-		constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
-		if (constraint_ns > 0) {
-			td->effective_constraint_ns = constraint_ns;
-			td->cached_suspend_ok = true;
-		} else {
-			td->effective_constraint_ns = 0;
-		}
+		constraint_ns -= td->suspend_latency_ns +
+				td->resume_latency_ns;
+		/*
+		 * effective_constraint_ns is zero already and cached_suspend_ok
+		 * is false, so if the computed value is not positive, return
+		 * right away.
+		 */
+		if (constraint_ns <= 0)
+			return false;
+
+		td->effective_constraint_ns = constraint_ns;
+		td->cached_suspend_ok = true;
 	}
 
 	/*
@@ -150,19 +168,13 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
 		 */
 		td = &to_gpd_data(pdd)->td;
 		constraint_ns = td->effective_constraint_ns;
-		/* default_suspend_ok() need not be called before us. */
-		if (constraint_ns < 0)
-			constraint_ns = dev_pm_qos_read_value(pdd->dev);
-
-		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
-			continue;
-
-		constraint_ns *= NSEC_PER_USEC;
-
 		/*
-		 * constraint_ns cannot be negative here, because the device has
-		 * been suspended.
+		 * Zero means "no suspend at all" and this runs only when all
+		 * devices in the domain are suspended, so it must be positive.
 		 */
+		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)
+			continue;
+
 		if (constraint_ns <= off_on_time_ns)
 			return false;