wimax/i2400m: make i2400m->bus_dev_{stop,start}() optional

In coming commits, the i2400m SDIO driver will not use
i2400m->bus_dev_stop().

Thus changed to check before calling, as an empty stub has more
overhead than a call to check if the function pointer is non-NULL.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>

drivers/net/wimax/i2400m/driver.c

@@ -384,9 +384,11 @@ int __i2400m_dev_start(struct i2400m *i2400m, enum i2400m_bri flags)
 		dev_err(dev, "cannot create workqueue\n");
 		goto error_create_workqueue;
 	}
-	result = i2400m->bus_dev_start(i2400m);
-	if (result < 0)
-		goto error_bus_dev_start;
+	if (i2400m->bus_dev_start) {
+		result = i2400m->bus_dev_start(i2400m);
+		if (result < 0)
+			goto error_bus_dev_start;
+	}
 	i2400m->ready = 1;
 	wmb();		/* see i2400m->ready's documentation  */
 	/* process pending reports from the device */
@@ -413,7 +415,8 @@ int __i2400m_dev_start(struct i2400m *i2400m, enum i2400m_bri flags)
 	wmb();		/* see i2400m->ready's documentation  */
 	flush_workqueue(i2400m->work_queue);
 error_fw_check:
-	i2400m->bus_dev_stop(i2400m);
+	if (i2400m->bus_dev_stop)
+		i2400m->bus_dev_stop(i2400m);
 error_bus_dev_start:
 	destroy_workqueue(i2400m->work_queue);
 error_create_workqueue:
@@ -480,7 +483,8 @@ void __i2400m_dev_stop(struct i2400m *i2400m)
 	wmb();		/* see i2400m->ready's documentation  */
 	flush_workqueue(i2400m->work_queue);
 
-	i2400m->bus_dev_stop(i2400m);
+	if (i2400m->bus_dev_stop)
+		i2400m->bus_dev_stop(i2400m);
 	destroy_workqueue(i2400m->work_queue);
 	i2400m_rx_release(i2400m);
 	i2400m_tx_release(i2400m);

drivers/net/wimax/i2400m/i2400m.h

@@ -245,19 +245,19 @@ struct i2400m_barker_db;
  *     all the host resources created to  handle communication with
  *     the device.
  *
- * @bus_dev_start: [fill] Function called by the bus-generic code
- *     [i2400m_dev_start()] to setup the bus-specific communications
- *     to the the device. See LIFE CYCLE above.
+ * @bus_dev_start: [optional fill] Function called by the bus-generic
+ *     code [i2400m_dev_start()] to do things needed to start the
+ *     device. See LIFE CYCLE above.
  *
  *     NOTE: Doesn't need to upload the firmware, as that is taken
  *     care of by the bus-generic code.
  *
- * @bus_dev_stop: [fill] Function called by the bus-generic code
- *     [i2400m_dev_stop()] to shutdown the bus-specific communications
- *     to the the device. See LIFE CYCLE above.
+ * @bus_dev_stop: [optional fill] Function called by the bus-generic
+ *     code [i2400m_dev_stop()] to do things needed for stopping the
+ *     device. See LIFE CYCLE above.
  *
  *     This function does not need to reset the device, just tear down
- *     all the host resources created to  handle communication with
+ *     all the host resources created to handle communication with
  *     the device.
  *
  * @bus_tx_kick: [fill] Function called by the bus-generic code to let