usb: udc: store usb_udc pointer in struct usb_gadget

Instead of iterate to find usb_udc according to usb_gadget, this
way is easier.

Alan Stern suggests this way too:
http://marc.info/?l=linux-usb&m=142168496528894&w=2

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/udc-core.c

@@ -128,21 +128,11 @@ EXPORT_SYMBOL_GPL(usb_gadget_giveback_request);
 
 static void usb_gadget_state_work(struct work_struct *work)
 {
-	struct usb_gadget	*gadget = work_to_gadget(work);
-	struct usb_udc		*udc = NULL;
-
-	mutex_lock(&udc_lock);
-	list_for_each_entry(udc, &udc_list, list)
-		if (udc->gadget == gadget)
-			goto found;
-	mutex_unlock(&udc_lock);
+	struct usb_gadget *gadget = work_to_gadget(work);
+	struct usb_udc *udc = gadget->udc;
 
-	return;
-
-found:
-	mutex_unlock(&udc_lock);
-
-	sysfs_notify(&udc->dev.kobj, NULL, "state");
+	if (udc)
+		sysfs_notify(&udc->dev.kobj, NULL, "state");
 }
 
 void usb_gadget_set_state(struct usb_gadget *gadget,
@@ -278,6 +268,7 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 		goto err3;
 
 	udc->gadget = gadget;
+	gadget->udc = udc;
 
 	mutex_lock(&udc_lock);
 	list_add_tail(&udc->list, &udc_list);
@@ -348,21 +339,14 @@ static void usb_gadget_remove_driver(struct usb_udc *udc)
  */
 void usb_del_gadget_udc(struct usb_gadget *gadget)
 {
-	struct usb_udc		*udc = NULL;
+	struct usb_udc *udc = gadget->udc;
 
-	mutex_lock(&udc_lock);
-	list_for_each_entry(udc, &udc_list, list)
-		if (udc->gadget == gadget)
-			goto found;
-
-	dev_err(gadget->dev.parent, "gadget not registered.\n");
-	mutex_unlock(&udc_lock);
-
-	return;
+	if (!udc)
+		return;
 
-found:
 	dev_vdbg(gadget->dev.parent, "unregistering gadget\n");
 
+	mutex_lock(&udc_lock);
 	list_del(&udc->list);
 	mutex_unlock(&udc_lock);
 

include/linux/usb/gadget.h

@@ -474,6 +474,7 @@ struct usb_dcd_config_params {
 
 struct usb_gadget;
 struct usb_gadget_driver;
+struct usb_udc;
 
 /* the rest of the api to the controller hardware: device operations,
  * which don't involve endpoints (or i/o).
@@ -496,6 +497,7 @@ struct usb_gadget_ops {
 /**
  * struct usb_gadget - represents a usb slave device
  * @work: (internal use) Workqueue to be used for sysfs_notify()
+ * @udc: struct usb_udc pointer for this gadget
  * @ops: Function pointers used to access hardware-specific operations.
  * @ep0: Endpoint zero, used when reading or writing responses to
  *	driver setup() requests
@@ -545,6 +547,7 @@ struct usb_gadget_ops {
  */
 struct usb_gadget {
 	struct work_struct		work;
+	struct usb_udc			*udc;
 	/* readonly to gadget driver */
 	const struct usb_gadget_ops	*ops;
 	struct usb_ep			*ep0;