usb: gadget: composite: add usb_remove_function()

This will be used to remove a single function from a given config. Right
now "ignore" that an error at ->bind() time and cleanup later during
composite_unbind() / remove_config().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/composite.c

@@ -215,6 +215,18 @@ done:
 }
 EXPORT_SYMBOL_GPL(usb_add_function);
 
+void usb_remove_function(struct usb_configuration *c, struct usb_function *f)
+{
+	if (f->disable)
+		f->disable(f);
+
+	bitmap_zero(f->endpoints, 32);
+	list_del(&f->list);
+	if (f->unbind)
+		f->unbind(c, f);
+}
+EXPORT_SYMBOL_GPL(usb_remove_function);
+
 /**
  * usb_function_deactivate - prevent function and gadget enumeration
  * @function: the function that isn't yet ready to respond

include/linux/usb/composite.h

@@ -461,6 +461,7 @@ struct usb_configuration *usb_get_config(struct usb_composite_dev *cdev,
 		int val);
 int usb_add_config_only(struct usb_composite_dev *cdev,
 		struct usb_configuration *config);
+void usb_remove_function(struct usb_configuration *c, struct usb_function *f);
 
 #define DECLARE_USB_FUNCTION(_name, _inst_alloc, _func_alloc)		\
 	static struct usb_function_driver _name ## usb_func = {		\