}
 
 static int dio_callback(struct comedi_device *dev,
-                       int dir, int port, int data, unsigned long arg)
+                       int dir, int port, int data, unsigned long iobase)
 {
-       void __iomem *iobase = (void __iomem *)arg;
-
        if (dir) {
-               writeb(data, iobase + port);
+               writeb(data, dev->mmio + iobase + port);
                return 0;
        }
-       return readb(iobase + port);
+       return readb(dev->mmio + iobase + port);
 }
 
 static int dio_callback_4020(struct comedi_device *dev,
                        ret = subdev_8255_init(dev, s, dio_callback_4020,
                                               (unsigned long)dio_8255_iobase);
                } else {
-                       dio_8255_iobase = dev->mmio + DIO_8255_OFFSET;
                        ret = subdev_8255_init(dev, s, dio_callback,
-                                              (unsigned long)dio_8255_iobase);
+                                              DIO_8255_OFFSET);
                }
                if (ret)
                        return ret;