USB: musb: do not work if no gadget driver is loaded

On OTG and gadget-only configurations, we need a gadget driver
in order to work properly, so avoid changing operation modes
when there's no gadget driver loaded.
Signed-off-by: NFelipe Balbi <felipe.balbi@nokia.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: NAnand Gadiyar <gadiyar@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/musb/musb_core.c

@@ -1521,6 +1521,14 @@ irqreturn_t musb_interrupt(struct musb *musb)
 		(devctl & MUSB_DEVCTL_HM) ? "host" : "peripheral",
 		musb->int_usb, musb->int_tx, musb->int_rx);
 
+#ifdef CONFIG_USB_GADGET_MUSB_HDRC
+	if (is_otg_enabled(musb) || is_peripheral_enabled(musb))
+		if (!musb->gadget_driver) {
+			DBG(5, "No gadget driver loaded\n");
+			return IRQ_HANDLED;
+		}
+#endif
+
 	/* the core can interrupt us for multiple reasons; docs have
 	 * a generic interrupt flowchart to follow
 	 */