linux-kernel - [PATCH v2 3/3] pmdommain: add support system-wide resume latency constraints

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Message-Id: <20260205-topic-lpm-pmdomain-device-constraints-v2-3-61f7be7d35ac@baylibre.com>
Date: Thu, 05 Feb 2026 16:29:57 -0800
From: "Kevin Hilman (TI)" <khilman@...libre.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, 
 Ulf Hansson <ulf.hansson@...aro.org>, linux-pm@...r.kernel.org
Cc: Dhruva Gole <d-gole@...com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] pmdommain: add support system-wide resume latency
 constraints

In addition to checking for CPU latency constraints when checking if
OK to power down a domain, also check for QoS latency constraints in
all devices of a domain and use that in determining the final latency
constraint to use for the domain.

Since cpu_system_power_down_ok() is used for system-wide suspend, the
per-device constratints are only relevant if the LATENCY_SYS QoS flag
is set.

Signed-off-by: Kevin Hilman (TI) <khilman@...libre.com>
---
 drivers/pmdomain/governor.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
index 96737abbb496..bbf59b93c8b6 100644
--- a/drivers/pmdomain/governor.c
+++ b/drivers/pmdomain/governor.c
@@ -13,6 +13,8 @@
 #include <linux/cpumask.h>
 #include <linux/ktime.h>
 
+#include "core.h"
+
 static int dev_update_qos_constraint(struct device *dev, void *data)
 {
 	s64 *constraint_ns_p = data;
@@ -425,17 +427,60 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	return true;
 }
 
+/**
+ * check_device_qos_latency - Callback to check device QoS latency constraints
+ * @dev: Device to check
+ * @data: Pointer to s32 variable holding minimum latency found so far
+ *
+ * This callback checks if the device has a system-wide resume latency QoS
+ * constraint and updates the minimum latency if this device has a stricter
+ * constraint.
+ *
+ * Returns: 0 to continue iteration.
+ */
+static int check_device_qos_latency(struct device *dev, void *data)
+{
+	s32 *min_dev_latency = data;
+	enum pm_qos_flags_status flag_status;
+	s32 dev_latency;
+
+	dev_latency = dev_pm_qos_read_value(dev, DEV_PM_QOS_RESUME_LATENCY);
+	flag_status = dev_pm_qos_flags(dev, PM_QOS_FLAG_LATENCY_SYS);
+	if ((dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) &&
+	    (flag_status == PM_QOS_FLAGS_ALL)) {
+		dev_dbg(dev,
+			"has QoS system-wide resume latency=%d\n",
+			dev_latency);
+		if (dev_latency < *min_dev_latency)
+			*min_dev_latency = dev_latency;
+	}
+
+	return 0;
+}
+
 static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
 {
 	s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
 	int state_idx = genpd->state_count - 1;
+	s32 min_dev_latency = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+	s64 min_dev_latency_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
 
 	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
 		genpd->state_idx = state_idx;
 		return true;
 	}
 
+	genpd_for_each_child(genpd, check_device_qos_latency,
+			     &min_dev_latency);
+
+	/* If device latency < CPU wakeup latency, use it instead */
+	if (min_dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
+		min_dev_latency_ns = min_dev_latency * NSEC_PER_USEC;
+		if (min_dev_latency_ns < constraint_ns)
+			constraint_ns = min_dev_latency_ns;
+	}
+
 	/* Find the deepest state for the latency constraint. */
 	while (state_idx >= 0) {
 		s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +

-- 
2.51.0