usb: add option to initialize USB device support at boot

Possibility to initialize USB device support is useful when
only CDC ACM class is enabled and CDC ACM UART is used as
backend for console, shell, or logging.

Signed-off-by: Johann Fischer <[email protected]>

Author: jfischer-no

subsys/usb/Kconfig

@@ -152,6 +152,12 @@ config USB_WORKQUEUE_PRIORITY
 	  priority. This means that any work handler, once started, won't
 	  be preempted by any other thread until finished.
 
+config USB_DEVICE_INITIALIZE_AT_BOOT
+	bool "Initialize USB device support at boot"
+	depends on USB_CDC_ACM
+	help
+	  Use CDC ACM UART as backend for console, shell, or logging.
+
 source "subsys/usb/class/Kconfig"
 
 endif # USB_DEVICE_STACK

subsys/usb/usb_device.c

@@ -1529,7 +1529,8 @@ int usb_enable(usb_dc_status_callback status_cb)
 	k_mutex_lock(&usb_enable_lock, K_FOREVER);
 
 	if (usb_dev.enabled == true) {
-		ret = 0;
+		LOG_WRN("USB device support already enabled");
+		ret = -EALREADY;
 		goto out;
 	}
 
@@ -1616,7 +1617,7 @@ static int usb_device_init(const struct device *dev)
 	uint8_t *device_descriptor;
 
 	if (usb_dev.enabled == true) {
-		return 0;
+		return -EALREADY;
 	}
 
 	/* register device descriptor */
@@ -1628,7 +1629,11 @@ static int usb_device_init(const struct device *dev)
 
 	usb_set_config(device_descriptor);
 
+	if (IS_ENABLED(CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT)) {
+		return usb_enable(NULL);
+	}
+
 	return 0;
 }
 
-SYS_INIT(usb_device_init, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEVICE);
+SYS_INIT(usb_device_init, POST_KERNEL, CONFIG_APPLICATION_INIT_PRIORITY);