staging: comedi: Add helper macro for comedi usb driver boilerplate

Introduce the module_comedi_usb_driver macro, and the
associated register/unregister functions, which is a
convenience macro for comedi usb driver modules similar
to module_platform_driver. It is intended to be used by
drivers where the init/exit section does nothing but
register/unregister the comedi driver and associated usb
driver. By using this macro it is possible to eliminate
a few lines of boilerplate code per comedi usb driver.

Also, when registering the usb driver check for failure
and unregister the comedi driver.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedidev.h

@@ -329,6 +329,25 @@ void comedi_pci_driver_unregister(struct comedi_driver *, struct pci_driver *);
 	module_driver(__comedi_driver, comedi_pci_driver_register, \
 			comedi_pci_driver_unregister, &(__pci_driver))
 
+struct usb_driver;
+
+int comedi_usb_driver_register(struct comedi_driver *, struct usb_driver *);
+void comedi_usb_driver_unregister(struct comedi_driver *, struct usb_driver *);
+
+/**
+ * module_comedi_usb_driver() - Helper macro for registering a comedi USB driver
+ * @__comedi_driver: comedi_driver struct
+ * @__usb_driver: usb_driver struct
+ *
+ * Helper macro for comedi USB drivers which do not do anything special
+ * in module init/exit. This eliminates a lot of boilerplate. Each
+ * module may only use this macro once, and calling it replaces
+ * module_init() and module_exit()
+ */
+#define module_comedi_usb_driver(__comedi_driver, __usb_driver) \
+	module_driver(__comedi_driver, comedi_usb_driver_register, \
+			comedi_usb_driver_unregister, &(__usb_driver))
+
 void init_polling(void);
 void cleanup_polling(void);
 void start_polling(struct comedi_device *);

drivers/staging/comedi/drivers.c

@@ -1016,3 +1016,30 @@ void comedi_usb_auto_unconfig(struct usb_interface *intf)
 	comedi_auto_unconfig(&intf->dev);
 }
 EXPORT_SYMBOL_GPL(comedi_usb_auto_unconfig);
+
+int comedi_usb_driver_register(struct comedi_driver *comedi_driver,
+		struct usb_driver *usb_driver)
+{
+	int ret;
+
+	ret = comedi_driver_register(comedi_driver);
+	if (ret < 0)
+		return ret;
+
+	ret = usb_register(usb_driver);
+	if (ret < 0) {
+		comedi_driver_unregister(comedi_driver);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_usb_driver_register);
+
+void comedi_usb_driver_unregister(struct comedi_driver *comedi_driver,
+		struct usb_driver *usb_driver)
+{
+	usb_deregister(usb_driver);
+	comedi_driver_unregister(comedi_driver);
+}
+EXPORT_SYMBOL_GPL(comedi_usb_driver_unregister);