usb: gadget: udc-core: introduce usb_add_gadget_udc_release()

not all UDC drivers need a proper release function,
for those which don't need it, we udc-core will provide
a no-op release method so we can remove "redefinition"
of such methods in almost every UDC driver.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc-core.c

@@ -166,15 +166,23 @@ static void usb_udc_release(struct device *dev)
 }
 
 static const struct attribute_group *usb_udc_attr_groups[];
+
+static void usb_udc_nop_release(struct device *dev)
+{
+	dev_vdbg(dev, "%s\n", __func__);
+}
+
 /**
- * usb_add_gadget_udc - adds a new gadget to the udc class driver list
- * @parent: the parent device to this udc. Usually the controller
- * driver's device.
- * @gadget: the gadget to be added to the list
+ * usb_add_gadget_udc_release - adds a new gadget to the udc class driver list
+ * @parent: the parent device to this udc. Usually the controller driver's
+ * device.
+ * @gadget: the gadget to be added to the list.
+ * @release: a gadget release function.
  *
  * Returns zero on success, negative errno otherwise.
  */
-int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget)
+int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
+		void (*release)(struct device *dev))
 {
 	struct usb_udc		*udc;
 	int			ret = -ENOMEM;
@@ -190,6 +198,13 @@ int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget)
 	gadget->dev.dma_parms = parent->dma_parms;
 	gadget->dev.dma_mask = parent->dma_mask;
 
+	if (release) {
+		gadget->dev.release = release;
+	} else {
+		if (!gadget->dev.release)
+			gadget->dev.release = usb_udc_nop_release;
+	}
+
 	ret = device_register(&gadget->dev);
 	if (ret)
 		goto err2;
@@ -231,6 +246,20 @@ int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget)
 err1:
 	return ret;
 }
+EXPORT_SYMBOL_GPL(usb_add_gadget_udc_release);
+
+/**
+ * usb_add_gadget_udc - adds a new gadget to the udc class driver list
+ * @parent: the parent device to this udc. Usually the controller
+ * driver's device.
+ * @gadget: the gadget to be added to the list
+ *
+ * Returns zero on success, negative errno otherwise.
+ */
+int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget)
+{
+	return usb_add_gadget_udc_release(parent, gadget, NULL);
+}
 EXPORT_SYMBOL_GPL(usb_add_gadget_udc);
 
 static void usb_gadget_remove_driver(struct usb_udc *udc)

include/linux/usb/gadget.h

@@ -874,6 +874,8 @@ int usb_gadget_probe_driver(struct usb_gadget_driver *driver);
  */
 int usb_gadget_unregister_driver(struct usb_gadget_driver *driver);
 
+extern int usb_add_gadget_udc_release(struct device *parent,
+		struct usb_gadget *gadget, void (*release)(struct device *dev));
 extern int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget);
 extern void usb_del_gadget_udc(struct usb_gadget *gadget);
 extern int udc_attach_driver(const char *name,