esp32: Make 'restart' function independent of Wi-Fi

Restart being a lower-layer system-level function, needn't depend on
the higher level Wi-Fi libraries.

This also enables us to get rid of one more WIFI_ENABLED ifdef check

components/esp32/event_default_handlers.c

@@ -23,6 +23,7 @@
 #include "esp_event_loop.h"
 #include "esp_task.h"
 #include "esp_eth.h"
+#include "esp_system.h"
 
 #include "rom/ets_sys.h"
 
@@ -413,5 +414,6 @@ esp_err_t esp_wifi_init(wifi_init_config_t *config)
      default_event_handlers[SYSTEM_EVENT_AP_START]         = system_event_ap_start_handle_default;
      default_event_handlers[SYSTEM_EVENT_AP_STOP]          = system_event_ap_stop_handle_default;
 
+     esp_register_shutdown_handler((shutdown_handler_t)esp_wifi_stop);
      return esp_wifi_init_internal(config);
 }

components/esp32/include/esp_system.h

@@ -49,6 +49,15 @@ void system_init(void) __attribute__ ((deprecated));
   */
 void system_restore(void) __attribute__ ((deprecated));
 
+typedef void (*shutdown_handler_t)(void);
+/**
+  * @brief  Register shutdown handler
+  *
+  * This function allows you to register a handler that gets invoked before a
+  * systematic shutdown of the chip.
+  */
+esp_err_t esp_register_shutdown_handler(shutdown_handler_t handle);
+
 /**
   * @brief  Restart PRO and APP CPUs.
   *

components/esp32/system_api.c

@@ -39,6 +39,9 @@ static const char* TAG = "system_api";
 
 static uint8_t base_mac_addr[6] = { 0 };
 
+#define SHUTDOWN_HANDLERS_NO 2
+static shutdown_handler_t shutdown_handlers[SHUTDOWN_HANDLERS_NO];
+
 void system_init()
 {
 }
@@ -227,23 +230,28 @@ esp_err_t esp_read_mac(uint8_t* mac, esp_mac_type_t type)
     return ESP_OK;
 }
 
-void esp_restart_noos() __attribute__ ((noreturn));
+esp_err_t esp_register_shutdown_handler(shutdown_handler_t handler)
-
-/* Dummy function to be used instead of esp_wifi_stop if WiFi stack is not
- * linked in (even though CONFIG_WIFI_ENABLED is set).
- */
-esp_err_t wifi_stop_noop()
 {
+     int i;
+     for (i = 0; i < SHUTDOWN_HANDLERS_NO; i++) {
+	  if (shutdown_handlers[i] == NULL) {
+	       shutdown_handlers[i] = handler;
 	       return ESP_OK;
 	  }
+     }
+     return ESP_FAIL;
+}
 
-esp_err_t esp_wifi_stop(void) __attribute((weak, alias("wifi_stop_noop")));
+void esp_restart_noos() __attribute__ ((noreturn));
 
 void IRAM_ATTR esp_restart(void)
 {
-#ifdef CONFIG_WIFI_ENABLED
+     int i;
-    esp_wifi_stop();
+     for (i = 0; i < SHUTDOWN_HANDLERS_NO; i++) {
-#endif
+	  if (shutdown_handlers[i]) {
+	       shutdown_handlers[i]();
+	  }
+     }
 
     // Disable scheduler on this core.
     vTaskSuspendAll();