usb: gadget: introduce 'enabled' flag in struct usb_ep

This patch introduces 'enabled' flag in struct usb_ep, and modifies
usb_ep_enable() and usb_ep_disable() functions to encapsulate endpoint
enabled/disabled state. It helps to avoid enabling endpoints which are
already enabled, and disabling endpoints which are already disables.

From now USB functions don't have to remember current endpoint
enable/disable state, as this state is now handled automatically which
makes this API less bug-prone.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

include/linux/usb/gadget.h

@@ -215,6 +215,7 @@ struct usb_ep {
 	struct list_head	ep_list;
 	struct usb_ep_caps	caps;
 	bool			claimed;
+	bool			enabled;
 	unsigned		maxpacket:16;
 	unsigned		maxpacket_limit:16;
 	unsigned		max_streams:16;
@@ -264,7 +265,18 @@ static inline void usb_ep_set_maxpacket_limit(struct usb_ep *ep,
  */
 static inline int usb_ep_enable(struct usb_ep *ep)
 {
-	return ep->ops->enable(ep, ep->desc);
+	int ret;
+
+	if (ep->enabled)
+		return 0;
+
+	ret = ep->ops->enable(ep, ep->desc);
+	if (ret)
+		return ret;
+
+	ep->enabled = true;
+
+	return 0;
 }
 
 /**
@@ -281,7 +293,18 @@ static inline int usb_ep_enable(struct usb_ep *ep)
  */
 static inline int usb_ep_disable(struct usb_ep *ep)
 {
-	return ep->ops->disable(ep);
+	int ret;
+
+	if (!ep->enabled)
+		return 0;
+
+	ret = ep->ops->disable(ep);
+	if (ret)
+		return ret;
+
+	ep->enabled = false;
+
+	return 0;
 }
 
 /**