Add capability to perform initial board initialization on a separate worker thread.

configs/sama5d4-ek/kernel/defconfig

@@ -419,6 +419,9 @@ CONFIG_NAME_MAX=32
 # RTOS hooks
 #
 CONFIG_BOARD_INITIALIZE=y
+CONFIG_BOARD_INITTHREAD=y
+CONFIG_BOARD_INITTHREAD_STACKSIZE=2048
+CONFIG_BOARD_INITTHREAD_PRIORITY=240
 # CONFIG_SCHED_STARTHOOK is not set
 # CONFIG_SCHED_ATEXIT is not set
 # CONFIG_SCHED_ONEXIT is not set

sched/Kconfig

@@ -651,6 +651,40 @@ config BOARD_INITIALIZE
 		phase may be used, for example, to initialize board-specific
 		device drivers.
 
+if BOARD_INITIALIZE
+
+config BOARD_INITTHREAD
+	bool "Board initialization thread"
+	default n
+	---help---
+		Some initialization operations cannot be performed on the start-up,
+		initialization thread.  That is because the initialization thread
+		cannot wait for event.  If waiting is required as part of the board
+		initialization then this option must be selected.  Waiting may be
+		required, for example, to mount a file system or or initialize a
+		device such as an SD card.
+
+if BOARD_INITTHREAD
+
+config BOARD_INITTHREAD_STACKSIZE
+	int "Board initialization thread stack size"
+	default 2048
+	---help---
+		The size of the stack to allocate when starting the board
+		initialization thread.
+
+config BOARD_INITTHREAD_PRIORITY
+	int "Board initialization thread priority"
+	default 240
+	---help---
+		The priority of the board initialization thread.  This priority is
+		not a critical setting.  No other application threads will be
+		started until the board initialization is completed.  Hence, there
+		is very little competition for the CPU.
+
+endif # BOARD_INITTHREAD
+endif # BOARD_INITIALIZE
+
 config SCHED_STARTHOOK
 	bool "Enable startup hook"
 	default n

sched/init/os_bringup.c

@@ -260,10 +260,11 @@ static inline void os_workqueues(void)
 #endif /* CONFIG_SCHED_WORKQUEUE */
 
 /****************************************************************************
- * Name: os_init_thread
+ * Name: os_start_application
  *
  * Description:
- *   Start the application initialization thread.
+ *   Execute the board initialization function (if so configured) and start
+ *   the application initialization thread.
  *
  * Input Parameters:
  *   None
@@ -274,18 +275,26 @@ static inline void os_workqueues(void)
  ****************************************************************************/
 
 #if defined(CONFIG_INIT_ENTRYPOINT)
-static inline void os_init_thread(void)
+static inline void os_do_appstart(void)
 {
   int taskid;
 
-  svdbg("Starting init thread\n");
+#ifdef CONFIG_BOARD_INITIALIZE
+  /* Perform any last-minute, board-specific initialization, if so
+   * configured.
+   */
 
-  /* Start the application initialization ask.  In a flat build, this is
+  board_initialize();
+#endif
+
+  /* Start the application initialization task.  In a flat build, this is
    * entrypoint is given by the definitions, CONFIG_USER_ENTRYPOINT.  In
    * the protected build, however, we must get the address of the
    * entrypoint from the header at the beginning of the user-space blob.
    */
 
+  svdbg("Starting init thread\n");
+
 #ifdef CONFIG_BUILD_PROTECTED
   DEBUGASSERT(USERSPACE->us_entrypoint != NULL);
   taskid = task_create("init", SCHED_PRIORITY_DEFAULT,
@@ -301,10 +310,23 @@ static inline void os_init_thread(void)
 }
 
 #elif defined(CONFIG_INIT_FILEPATH)
-static inline void os_init_thread(void)
+static inline void os_do_appstart(void)
 {
   int ret;
 
+#ifdef CONFIG_BOARD_INITIALIZE
+  /* Perform any last-minute, board-specific initialization, if so
+   * configured.
+   */
+
+  board_initialize();
+#endif
+
+  /* Start the application initialization program from a program in a
+   * mounted file system.  Presumably the file system was mounted as part
+   * of the board_initialize() operation.
+   */
+
   svdbg("Starting init task: %s\n", CONFIG_USER_INITPATH);
 
   ret = exec(CONFIG_USER_INITPATH, NULL, CONFIG_INIT_SYMTAB,
@@ -313,13 +335,78 @@ static inline void os_init_thread(void)
 }
 
 #elif defined(CONFIG_INIT_NONE)
-#  define os_init_thread()
+#  define os_do_appstart()
 
 #else
 #  error "Cannot start initialization thread"
 
 #endif
 
+/****************************************************************************
+ * Name: os_start_task
+ *
+ * Description:
+ *   This is the framework for a short duration worker thread.  It off-loads
+ *   the board initialization and application start-up from the limited
+ *   start-up, initialization thread to a more robust kernel thread.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   None
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_BOARD_INITTHREAD
+static int os_start_task(int argc, FAR char **argv)
+{
+  /* Do the board/application initialization and exit */
+
+  os_do_appstart();
+  return OK;
+}
+#endif
+
+/****************************************************************************
+ * Name: os_start_application
+ *
+ * Description:
+ *   Execute the board initialization function (if so configured) and start
+ *   the application initialization thread.  This will be done either on the
+ *   thread of execution of the caller or on a separate thread of execution
+ *   if so configured.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   None
+ *
+ ****************************************************************************/
+
+static inline void os_start_application(void)
+{
+#ifdef CONFIG_BOARD_INITTHREAD
+  int taskid;
+
+  /* Do the board/application initialization on a separate thread of
+   * execution.
+   */
+
+  taskid = kernel_thread("AppBringUp", CONFIG_BOARD_INITTHREAD_PRIORITY,
+                         CONFIG_BOARD_INITTHREAD_STACKSIZE,
+                         (main_t)os_start_task, (FAR char * const *)NULL);
+  ASSERT(taskid > 0);
+
+#else
+  /* Do the board/application initialization on this thread of execution. */
+
+  os_do_appstart();
+
+#endif
+}
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -384,20 +471,12 @@ int os_bringup(void)
 
   os_workqueues();
 
-  /* Perform any last-minute, board-specific initialization, if so
-   * configured.
-   */
-
-#ifdef CONFIG_BOARD_INITIALIZE
-  board_initialize();
-#endif
-
   /* Once the operating system has been initialized, the system must be
    * started by spawning the user initialization thread of execution.  This
-   * is the first user-mode thread.
+   * will be the first user-mode thread.
    */
 
-  os_init_thread();
+  os_start_application();
 
   /* We an save a few bytes by discarding the IDLE thread's environment. */