PM / QoS: Fix device resume latency framework

The special value of 0 for device resume latency PM QoS means
"no restriction", but there are two problems with that.

First, device resume latency PM QoS requests with 0 as the
value are always put in front of requests with positive
values in the priority lists used internally by the PM QoS
framework, causing 0 to be chosen as an effective constraint
value.  However, that 0 is then interpreted as "no restriction"
effectively overriding the other requests with specific
restrictions which is incorrect.

Second, the users of device resume latency PM QoS have no
way to specify that *any* resume latency at all should be
avoided, which is an artificial limitation in general.

To address these issues, modify device resume latency PM QoS to
use S32_MAX as the "no constraint" value and 0 as the "no
latency at all" one and rework its users (the cpuidle menu
governor, the genpd QoS governor and the runtime PM framework)
to follow these changes.

Also add a special "n/a" value to the corresponding user space I/F
to allow user space to indicate that it cannot accept any resume
latencies at all for the given device.

Fixes: 85dc0b8a4019 (PM / QoS: Make it possible to expose PM QoS latency constraints)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323
Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Ramesh Thomas <ramesh.thomas@intel.com>

1 files changed, 16 insertions, 24 deletions

diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
index e4cca8adab32..99896fbf18e4 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -33,15 +33,10 @@ static int dev_update_qos_constraint(struct device *dev, void *data)
 		 * known at this point anyway).
 		 */
 		constraint_ns = dev_pm_qos_read_value(dev);
-		if (constraint_ns > 0)
-			constraint_ns *= NSEC_PER_USEC;
+		constraint_ns *= NSEC_PER_USEC;
 	}
 
-	/* 0 means "no constraint" */
-	if (constraint_ns == 0)
-		return 0;
-
-	if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
+	if (constraint_ns < *constraint_ns_p)
 		*constraint_ns_p = constraint_ns;
 
 	return 0;
@@ -69,12 +64,12 @@ 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);
 
-	if (constraint_ns < 0)
+	if (constraint_ns == 0)
 		return false;
 
 	constraint_ns *= NSEC_PER_USEC;
@@ -87,25 +82,25 @@ static bool default_suspend_ok(struct device *dev)
 		device_for_each_child(dev, &constraint_ns,
 				      dev_update_qos_constraint);
 
-	if (constraint_ns == 0) {
+	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS) {
 		/* "No restriction", so the device is allowed to suspend. */
-		td->effective_constraint_ns = 0;
+		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
 		td->cached_suspend_ok = true;
-	} else if (constraint_ns < 0) {
+	} else if (constraint_ns == 0) {
 		/*
 		 * This triggers if one of the children that don't belong to a
-		 * domain has a negative PM QoS constraint and it's better not
-		 * to suspend then.  effective_constraint_ns is negative already
-		 * and cached_suspend_ok is false, so bail out.
+		 * 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;
 		/*
-		 * effective_constraint_ns is negative already and
-		 * cached_suspend_ok is false, so if the computed value is not
-		 * positive, return right away.
+		 * 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;
@@ -174,13 +169,10 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
 		td = &to_gpd_data(pdd)->td;
 		constraint_ns = td->effective_constraint_ns;
 		/*
-		 * Negative values mean "no suspend at all" and this runs only
-		 * when all devices in the domain are suspended, so it must be
-		 * 0 at least.
-		 *
-		 * 0 means "no constraint"
+		 * 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 == 0)
+		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)
 			continue;
 
 		if (constraint_ns <= off_on_time_ns)