int composite_dev_prepare(struct usb_composite_driver *composite,
		struct usb_composite_dev *cdev)
{
	struct usb_gadget *gadget = cdev->gadget;
	int ret = -ENOMEM;

	/* preallocate control response and buffer */
	cdev->req = usb_ep_alloc_request(gadget->ep0, GFP_KERNEL);
	if (!cdev->req)
		return -ENOMEM;

	cdev->req->buf = kzalloc(USB_COMP_EP0_BUFSIZ, GFP_KERNEL);
	if (!cdev->req->buf)
		goto fail;

	ret = device_create_file(&gadget->dev, &dev_attr_suspended);
	if (ret)
		goto fail_dev;

	cdev->req->complete = composite_setup_complete;
	cdev->req->context = cdev;
	gadget->ep0->driver_data = cdev;

	cdev->driver = composite;

	/*
	 * As per USB compliance update, a device that is actively drawing
	 * more than 100mA from USB must report itself as bus-powered in
	 * the GetStatus(DEVICE) call.
	 */
	if (CONFIG_USB_GADGET_VBUS_DRAW <= USB_SELF_POWER_VBUS_MAX_DRAW)
		usb_gadget_set_selfpowered(gadget);

	/* interface and string IDs start at zero via kzalloc.
	 * we force endpoints to start unassigned; few controller
	 * drivers will zero ep->driver_data.
	 */
	usb_ep_autoconfig_reset(gadget);
	return 0;
fail_dev:
	kfree(cdev->req->buf);
fail:
	usb_ep_free_request(gadget->ep0, cdev->req);
	cdev->req = NULL;
	return ret;
}