USB host CDC/ACM driver requires CONFIG_SERIAL_REMOVABLE

TODO

@@ -1126,7 +1126,6 @@ o USB (drivers/usbdev, drivers/usbhost)
                 the RX reception logic probably should be moved to its own
                 dedicated thread.
 
-
                Most of these problems are unique to the Olimex LPC1766STK
                DCD; some are probably design problems in the CDC/ACM host
                driver.  The bottom line is that the host CDC/ACM driver is

drivers/usbhost/Kconfig

@@ -90,6 +90,7 @@ config USBHOST_CDCACM
 	default n
 	depends on USBHOST_HAVE_ASYNCH && !USBHOST_BULK_DISABLE && !USBHOST_INT_DISABLE
 	select USBHOST_ASYNCH
+	select SERIAL_REMOVABLE
 	---help---
 		Select this option to build in host support for CDC/ACM serial
 		devices.

drivers/usbhost/usbhost_cdcacm.c

@@ -99,6 +99,10 @@
 #  warning Asynchronous transfer support is required (CONFIG_USBHOST_ASYNCH)
 #endif
 
+#ifndef CONFIG_SERIAL_REMOVABLE
+#  warning Removable serial device support is required (CONFIG_SERIAL_REMOVABLE)
+#endif
+
 #ifdef CONFIG_USBHOST_CDCACM_NTDELAY
 #  define USBHOST_CDCACM_NTDELAY MSEC2TICK(CONFIG_USBHOST_CDCACM_NTDELAY)
 #else
@@ -2102,6 +2106,12 @@ static int usbhost_disconnected(struct usbhost_class_s *usbclass)
   flags              = irqsave();
   priv->disconnected = true;
 
+  /* Let the upper half driver know that serial device is no longer
+   * connected.
+   */
+
+  uart_connected(&priv->uartdev, false);
+
   /* Cancel any ongoing Bulk transfers */
 
   ret = DRVR_CANCEL(hport->drvr, priv->bulkin);