unsigned long flags;
        int result;
        int i;
+       int buf_len;
        char *buf_ptr = port->write_urb->transfer_buffer;
        dbg("%s - enter", __func__);
 
+       spin_lock_irqsave(&priv->lock, flags);
        *buf_ptr++ = IUU_UART_ESC;
        *buf_ptr++ = IUU_UART_TX;
        *buf_ptr++ = priv->writelen;
 
-       memcpy(buf_ptr, priv->writebuf,
-              priv->writelen);
+       memcpy(buf_ptr, priv->writebuf, priv->writelen);
+       buf_len = priv->writelen;
+       priv->writelen = 0;
+       spin_unlock_irqrestore(&priv->lock, flags);
        if (debug == 1) {
-               for (i = 0; i < priv->writelen; i++)
+               for (i = 0; i < buf_len; i++)
                        sprintf(priv->dbgbuf + i*2 ,
                                "%02X", priv->writebuf[i]);
-               priv->dbgbuf[priv->writelen+i*2] = 0;
+               priv->dbgbuf[buf_len+i*2] = 0;
                dbg("%s - writing %i chars : %s", __func__,
-                   priv->writelen, priv->dbgbuf);
+                   buf_len, priv->dbgbuf);
        }
        usb_fill_bulk_urb(port->write_urb, port->serial->dev,
                          usb_sndbulkpipe(port->serial->dev,
                                          port->bulk_out_endpointAddress),
-                         port->write_urb->transfer_buffer, priv->writelen + 3,
+                         port->write_urb->transfer_buffer, buf_len + 3,
                          iuu_rxcmd, port);
        result = usb_submit_urb(port->write_urb, GFP_ATOMIC);
-       spin_lock_irqsave(&priv->lock, flags);
-       priv->writelen = 0;
-       spin_unlock_irqrestore(&priv->lock, flags);
        usb_serial_port_softint(port);
        return result;
 }
                return -ENOMEM;
 
        spin_lock_irqsave(&priv->lock, flags);
-       if (priv->writelen > 0) {
-               /* buffer already filled but not commited */
-               spin_unlock_irqrestore(&priv->lock, flags);
-               return 0;
-       }
+
        /* fill the buffer */
-       memcpy(priv->writebuf, buf, count);
-       priv->writelen = count;
+       memcpy(priv->writebuf + priv->writelen, buf, count);
+       priv->writelen += count;
        spin_unlock_irqrestore(&priv->lock, flags);
 
        return count;