pm: device_runtime: Use its own queue

Device runtime is using the system workqueue to do operations
that are mostly blockers (suspend a device). This should not happen.

This commit defines a queue for the device runtime async operations.

The test for this API was assuming that the system workqueue
priority (which is cooperative) so we need to change the test priority
to be lower than the device runtime workqueue priority.

Signed-off-by: Flavio Ceolin <[email protected]>

Author: ceolin

subsys/pm/Kconfig

@@ -121,6 +121,25 @@ config PM_DEVICE_RUNTIME
 	  enabled, devices can be suspended or resumed based on the device
 	  usage even while the CPU or system is running.
 
+if PM_DEVICE_RUNTIME
+config PM_DEVICE_RUNTIME_WQ_STACK_SIZE
+	int "Stack size for pm runtime async workqueue"
+	default 1024
+	help
+	  Defines the size of the stack on the workqueue used for
+	  async operations.
+
+config PM_DEVICE_RUNTIME_WQ_PRIO
+	int "PM device runtime workqueue priority. Should be pre-emptible."
+	default 0
+
+config PM_DEVICE_RUNTIME_WQ_INIT_PRIO
+	int "PM device runtime workqueue init priority"
+	default 50
+	help
+	  Init priority level to setup the device runtime workqueue.
+endif # PM_DEVICE_RUNTIME
+
 config PM_DEVICE_SHELL
 	bool "Device Power Management shell"
 	depends on SHELL

subsys/pm/device_runtime.c

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2018 Intel Corporation.
  * Copyright (c) 2021 Nordic Semiconductor ASA.
+ * Copyright (c) 2025 HubbleNetwork.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -19,6 +20,9 @@ LOG_MODULE_DECLARE(pm_device, CONFIG_PM_DEVICE_LOG_LEVEL);
 #define PM_DOMAIN(_pm) NULL
 #endif
 
+K_THREAD_STACK_DEFINE(pm_device_runtime_stack, CONFIG_PM_DEVICE_RUNTIME_WQ_STACK_SIZE);
+static struct k_work_q pm_device_runtime_wq;
+
 #define EVENT_STATE_ACTIVE	BIT(PM_DEVICE_STATE_ACTIVE)
 #define EVENT_STATE_SUSPENDED	BIT(PM_DEVICE_STATE_SUSPENDED)
 
@@ -79,7 +83,7 @@ static int runtime_suspend(const struct device *dev, bool async,
 	if (async) {
 		/* queue suspend */
 		pm->base.state = PM_DEVICE_STATE_SUSPENDING;
-		(void)k_work_schedule(&pm->work, delay);
+		(void)k_work_schedule_for_queue(&pm_device_runtime_wq, &pm->work, delay);
 	} else {
 		/* suspend now */
 		ret = pm->base.action_cb(pm->dev, PM_DEVICE_ACTION_SUSPEND);
@@ -569,3 +573,18 @@ int pm_device_runtime_usage(const struct device *dev)
 
 	return dev->pm_base->usage;
 }
+
+static int pm_device_runtime_wq_init(void)
+{
+	const struct k_work_queue_config cfg = {.name = "PM DEVICE RUNTIME WQ"};
+
+	k_work_queue_init(&pm_device_runtime_wq);
+
+	k_work_queue_start(&pm_device_runtime_wq, pm_device_runtime_stack,
+			   K_THREAD_STACK_SIZEOF(pm_device_runtime_stack),
+			   CONFIG_PM_DEVICE_RUNTIME_WQ_PRIO, &cfg);
+
+	return 0;
+}
+
+SYS_INIT(pm_device_runtime_wq_init, POST_KERNEL, CONFIG_PM_DEVICE_RUNTIME_WQ_INIT_PRIO);

tests/subsys/pm/device_runtime_api/prj.conf

@@ -3,3 +3,4 @@ CONFIG_PM=y
 CONFIG_PM_DEVICE=y
 CONFIG_PM_DEVICE_RUNTIME=y
 CONFIG_MP_MAX_NUM_CPUS=1
+CONFIG_ZTEST_THREAD_PRIORITY=3

tests/subsys/pm/device_runtime_api/src/main.c

@@ -200,7 +200,7 @@ ZTEST(device_runtime_api, test_api)
 		 */
 		k_thread_create(&get_runner_td, get_runner_stack,
 				K_THREAD_STACK_SIZEOF(get_runner_stack), get_runner,
-				NULL, NULL, NULL, CONFIG_SYSTEM_WORKQUEUE_PRIORITY, 0,
+				NULL, NULL, NULL, CONFIG_PM_DEVICE_RUNTIME_WQ_PRIO, 0,
 				K_NO_WAIT);
 		k_yield();