core: introduce a system work queue, use it for EDF

Currently the EDF scheduler under Zephyr defines a delayed work queue
to be run on the primary core. However such a work queue will be
useful to multiple subsystems. Extract it from the EDF scheduler and
make it globally available.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

Author: lyakh

zephyr/CMakeLists.txt

@@ -528,6 +528,7 @@ zephyr_library_sources(
 	lib/alloc.c
 	lib/cpu.c
 	lib/pm_runtime.c
+	lib/primary.c
 
 	# Common library functions - Will be moved to Zephyr over time
 	lib.c

zephyr/Kconfig

@@ -89,4 +89,10 @@ config VIRTUAL_HEAP
 	help
 	  Enabling this option will use the virtual memory heap allocator to allocate buffers.
 	  It is based on a set of buffers whose size is predetermined.
+
+config SOF_PRIMARY_WQ_STACK_SZ
+	int "Primary work queue stack size"
+	default 8192
+	help
+	  Stack size for the primary core system work queue.
 endif

zephyr/edf_schedule.c

@@ -13,9 +13,6 @@
 #include <zephyr/kernel.h>
 #include <zephyr/sys_clock.h>
 
-static struct k_work_q edf_workq;
-static K_THREAD_STACK_DEFINE(edf_workq_stack, 8192);
-
 /*
  * since only IPC is using the EDF scheduler - we schedule the work in the
  * next timer_domain time slice
@@ -39,9 +36,7 @@ static void edf_work_handler(struct k_work *work)
 		if (deadline > now)
 			timeout = K_TICKS(deadline - now);
 
-		k_work_reschedule_for_queue(&edf_workq,
-					    &task->z_delayed_work,
-					    timeout);
+		sof_primary_wq_reschedule(&task->z_delayed_work, timeout);
 		task->state = SOF_TASK_STATE_QUEUED;
 	} else {
 		task_complete(task);
@@ -56,9 +51,7 @@ static int schedule_edf_task(void *data, struct task *task, uint64_t start,
 	/* start time is microseconds from now */
 	k_timeout_t start_time = K_USEC(start + EDF_SCHEDULE_DELAY);
 
-	k_work_reschedule_for_queue(&edf_workq,
-				    &task->z_delayed_work,
-				    start_time);
+	sof_primary_wq_reschedule(&task->z_delayed_work, start_time);
 
 	task->state = SOF_TASK_STATE_QUEUED;
 	return 0;
@@ -100,22 +93,9 @@ static struct scheduler_ops schedule_edf_ops = {
 
 int scheduler_init_edf(void)
 {
-	struct k_thread *thread = &edf_workq.thread;
-
 	scheduler_init(SOF_SCHEDULE_EDF, &schedule_edf_ops, NULL);
 
-	k_work_queue_start(&edf_workq,
-		       edf_workq_stack,
-		       K_THREAD_STACK_SIZEOF(edf_workq_stack),
-		       EDF_ZEPHYR_PRIORITY, NULL);
-
-	k_thread_suspend(thread);
-
-	k_thread_cpu_mask_clear(thread);
-	k_thread_cpu_mask_enable(thread, PLATFORM_PRIMARY_CORE_ID);
-	k_thread_name_set(thread, "edf_workq");
-
-	k_thread_resume(thread);
+	sof_primary_wq_init();
 
 	return 0;
 }

zephyr/include/sof/lib/cpu.h

@@ -93,6 +93,11 @@ static inline int cpu_secondary_cores_prepare_d0ix(void) { return 0; };
 
 #endif /* CONFIG_MULTICORE && CONFIG_SMP */
 
+#include <rtos/kernel.h>
+struct k_work_delayable;
+void sof_primary_wq_init(void);
+void sof_primary_wq_reschedule(struct k_work_delayable *dwork, k_timeout_t delay);
+
 #endif
 
 #endif /* __SOF_LIB_CPU_H__ */

zephyr/lib/primary.c

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Copyright(c) 2025 Intel Corporation.
+ */
+
+#include <zephyr/arch/cpu.h>
+#include <zephyr/kernel.h>
+
+#include <sof/lib/cpu.h>
+
+static struct k_work_q sof_prime_wq;
+static K_THREAD_STACK_DEFINE(sof_prime_wq_stack, CONFIG_SOF_PRIMARY_WQ_STACK_SZ);
+static atomic_val_t sof_prime_wq_init;
+
+void sof_primary_wq_reschedule(struct k_work_delayable *dwork, k_timeout_t delay)
+{
+	k_work_schedule_for_queue(&sof_prime_wq, dwork, delay);
+}
+
+void sof_primary_wq_init(void)
+{
+	if (atomic_set(&sof_prime_wq_init, 1))
+		return;
+
+	struct k_thread *thread = &sof_prime_wq.thread;
+
+	k_work_queue_start(&sof_prime_wq, sof_prime_wq_stack,
+			   K_THREAD_STACK_SIZEOF(sof_prime_wq_stack), 1, NULL);
+
+	k_thread_suspend(thread);
+
+	k_thread_cpu_pin(thread, PLATFORM_PRIMARY_CORE_ID);
+	k_thread_name_set(thread, "sof_prime_wq");
+
+	k_thread_resume(thread);
+}