wimax: document why wimax_msg_*() operations can be used in any state

Funcion documentation for wimax_msg_alloc() and wimax_msg_send() needs
to clarify that they can be used in the very early stages of a
wimax_dev lifecycle.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>

net/wimax/op-msg.c

@@ -108,6 +108,12 @@
  * Don't use skb_push()/skb_pull()/skb_reserve() on the skb, as
  * wimax_msg_send() depends on skb->data being placed at the
  * beginning of the user message.
+ *
+ * Unlike other WiMAX stack calls, this call can be used way early,
+ * even before wimax_dev_add() is called, as long as the
+ * wimax_dev->net_dev pointer is set to point to a proper
+ * net_dev. This is so that drivers can use it early in case they need
+ * to send stuff around or communicate with user space.
  */
 struct sk_buff *wimax_msg_alloc(struct wimax_dev *wimax_dev,
 				const char *pipe_name,
@@ -115,7 +121,7 @@ struct sk_buff *wimax_msg_alloc(struct wimax_dev *wimax_dev,
 				gfp_t gfp_flags)
 {
 	int result;
-	struct device *dev = wimax_dev->net_dev->dev.parent;
+	struct device *dev = wimax_dev_to_dev(wimax_dev);
 	size_t msg_size;
 	void *genl_msg;
 	struct sk_buff *skb;
@@ -161,7 +167,6 @@ error_genlmsg_put:
 error_new:
 	nlmsg_free(skb);
 	return ERR_PTR(result);
-
 }
 EXPORT_SYMBOL_GPL(wimax_msg_alloc);
 
@@ -256,10 +261,16 @@ EXPORT_SYMBOL_GPL(wimax_msg_len);
  * Don't use skb_push()/skb_pull()/skb_reserve() on the skb, as
  * wimax_msg_send() depends on skb->data being placed at the
  * beginning of the user message.
+ *
+ * Unlike other WiMAX stack calls, this call can be used way early,
+ * even before wimax_dev_add() is called, as long as the
+ * wimax_dev->net_dev pointer is set to point to a proper
+ * net_dev. This is so that drivers can use it early in case they need
+ * to send stuff around or communicate with user space.
  */
 int wimax_msg_send(struct wimax_dev *wimax_dev, struct sk_buff *skb)
 {
-	struct device *dev = wimax_dev->net_dev->dev.parent;
+	struct device *dev = wimax_dev_to_dev(wimax_dev);
 	void *msg = skb->data;
 	size_t size = skb->len;
 	might_sleep();