pm: device_runtime: Allow to use a dedicated wq

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

This commit adds an option to use dedicated 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 +121,51 @@ 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_DRIVER_NEEDS_DEDICATED_WQ
+	bool
+
+choice PM_DEVICE_RUNTIME_WQ
+	prompt "Work queue to be used by pm device runtime async"
+	default PM_DEVICE_RUNTIME_USE_DEDICATED_WQ if PM_DRIVER_NEEDS_DEDICATED_WQ
+	default PM_DEVICE_RUNTIME_USE_SYSTEM_WQ
+
+config PM_DEVICE_RUNTIME_USE_SYSTEM_WQ
+	bool "Use the system workqueue"
+	help
+	  When this option is enabled the power management subsystem will
+	  use the system worqueue instead of defining its own queue.
+
+config PM_DEVICE_RUNTIME_USE_DEDICATED_WQ
+	bool "Use a dedicated workqueue"
+	help
+	  When this option is enabled the power management subsystem will
+	  use a dedicated worqueue instead of the system work queue.
+
+if PM_DEVICE_RUNTIME_USE_DEDICATED_WQ
+config PM_DEVICE_RUNTIME_DEDICATED_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_DEDICATED_WQ_PRIO
+	int "PM device runtime workqueue priority. Should be pre-emptible."
+	default SYSTEM_WORKQUEUE_PRIORITY if PM_DEVICE_RUNTIME_USE_SYSTEM_WQ
+	default 0
+
+config PM_DEVICE_RUNTIME_DEDICATED_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_USE_DEDICATED_WQ
+endchoice
+
+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 +20,11 @@ LOG_MODULE_DECLARE(pm_device, CONFIG_PM_DEVICE_LOG_LEVEL);
 #define PM_DOMAIN(_pm) NULL
 #endif
 
+#ifdef CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ
+K_THREAD_STACK_DEFINE(pm_device_runtime_stack, CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_STACK_SIZE);
+static struct k_work_q pm_device_runtime_wq;
+#endif /* CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ */
+
 #define EVENT_STATE_ACTIVE	BIT(PM_DEVICE_STATE_ACTIVE)
 #define EVENT_STATE_SUSPENDED	BIT(PM_DEVICE_STATE_SUSPENDED)
 
@@ -79,7 +85,11 @@ static int runtime_suspend(const struct device *dev, bool async,
 	if (async) {
 		/* queue suspend */
 		pm->base.state = PM_DEVICE_STATE_SUSPENDING;
+#ifdef CONFIG_PM_DEVICE_RUNTIME_USE_SYSTEM_WQ
 		(void)k_work_schedule(&pm->work, delay);
+#else
+		(void)k_work_schedule_for_queue(&pm_device_runtime_wq, &pm->work, delay);
+#endif /* CONFIG_PM_DEVICE_RUNTIME_USE_SYSTEM_WQ */
 	} else {
 		/* suspend now */
 		ret = pm->base.action_cb(pm->dev, PM_DEVICE_ACTION_SUSPEND);
@@ -569,3 +579,23 @@ int pm_device_runtime_usage(const struct device *dev)
 
 	return dev->pm_base->usage;
 }
+
+#ifdef CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ
+
+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_DEDICATED_WQ_PRIO, &cfg);
+
+	return 0;
+}
+
+SYS_INIT(pm_device_runtime_wq_init, POST_KERNEL,
+	CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_INIT_PRIO);
+
+#endif /* CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ */

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

@@ -9,6 +9,7 @@
 #include <zephyr/pm/device_runtime.h>
 
 #include "test_driver.h"
+#include "zephyr/sys/util_macro.h"
 
 static const struct device *test_dev;
 static struct k_thread get_runner_td;
@@ -200,8 +201,9 @@ 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,
-				K_NO_WAIT);
+				NULL, NULL, NULL, COND_CODE_1(CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ,
+				(CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_PRIO),
+				(CONFIG_SYSTEM_WORKQUEUE_PRIORITY)), 0, K_NO_WAIT);
 		k_yield();
 
 		/* let driver suspend to finish and wait until get_runner finishes

tests/subsys/pm/device_runtime_api/testcase.yaml

@@ -10,3 +10,8 @@ tests:
     - native_sim
     extra_configs:
     - CONFIG_TEST_PM_DEVICE_ISR_SAFE=y
+  pm.device_runtime.async_dedicated_wq.api:
+    platform_allow:
+    - native_sim
+    extra_configs:
+    - CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ=y