schedule: config to build LL without task rescheduling

adds a config to instantiate the low-latency scheduler without task
rescheduling, given that the operation is optional.

Signed-off-by: Johny Lin <johnylin@google.com>
(cherry picked from commit 7648066)

src/schedule/Kconfig

@@ -41,3 +41,13 @@ config SCHEDULE_LL_STATS_LOG_WINDOW_SIZE
 	  Size of the statistics window as a power of two. The window size
 	  setting also impacts the rate of reporting. With 1ms scheduler tick,
 	  default of 10 results in 1024msec window size.
+
+config SCHEDULE_LL_NO_RESCHEDULE_TASK
+	bool "Low-latency scheduler skips task rescheduling"
+	default n
+	help
+	  Select this to instantiate the low-latency scheduler without task
+	  rescheduling, given that the operation is optional. Under such cases,
+	  scheduler_ops::reschedule_task will set to NULL instead, tasks with
+	  the attempt to reschedule (e.g. DMA trace works) will be relinguished
+	  directly and return no error.

src/schedule/ll_schedule.c

@@ -684,6 +684,11 @@ static int schedule_ll_task_cancel(void *data, struct task *task)
 	return 0;
 }
 
+#if CONFIG_SCHEDULE_LL_NO_RESCHEDULE_TASK
+/* As a null function pointer */
+#define reschedule_ll_task ((void*)0)
+
+#else
 static int reschedule_ll_task(void *data, struct task *task, uint64_t start)
 {
 	struct ll_schedule_data *sch = data;
@@ -717,6 +722,7 @@ static int reschedule_ll_task(void *data, struct task *task, uint64_t start)
 
 	return 0;
 }
+#endif
 
 static void scheduler_free_ll(void *data, uint32_t flags)
 {