net: Expose some errors generated in net_init

net_init does not always succeed, and there is no existing mechanism to
discover errors. This patch allows callers of net_init (such as net_init)
to handle errors. The root issue is that eth_get_dev can fail, but
net_init_loop doesn't expose that. The ideal way to fix eth_get_dev would
be to return an error with ERR_PTR, but there are a lot of callers, and all
of them just check if it's NULL. Another approach would be to change the
signature to something like

int eth_get_dev(struct udevice **pdev)

but that would require rewriting all of the many callers.
Signed-off-by: NSean Anderson <seanga2@gmail.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

include/net.h

@@ -593,7 +593,7 @@ extern int net_ntp_time_offset;			/* offset time from UTC */
 #endif
 
 /* Initialize the network adapter */
-void net_init(void);
+int net_init(void);
 int net_loop(enum proto_t);
 
 /* Load failed.	 Start again. */

net/eth-uclass.c

@@ -75,6 +75,9 @@ struct udevice *eth_get_dev(void)
 	struct eth_uclass_priv *uc_priv;
 
 	uc_priv = eth_get_uclass_priv();
+	if (!uc_priv)
+		return NULL;
+
 	if (!uc_priv->current)
 		eth_errno = uclass_first_device(UCLASS_ETH,
 				    &uc_priv->current);

net/net.c

@@ -338,12 +338,19 @@ void net_auto_load(void)
 	tftp_start(TFTPGET);
 }
 
-static void net_init_loop(void)
+static int net_init_loop(void)
 {
 	if (eth_get_dev())
 		memcpy(net_ethaddr, eth_get_ethaddr(), 6);
+	else
+		/*
+		 * Not ideal, but there's no way to get the actual error, and I
+		 * don't feel like fixing all the users of eth_get_dev to deal
+		 * with errors.
+		 */
+		return -ENONET;
 
-	return;
+	return 0;
 }
 
 static void net_clear_handlers(void)
@@ -358,7 +365,7 @@ static void net_cleanup_loop(void)
 	net_clear_handlers();
 }
 
-void net_init(void)
+int net_init(void)
 {
 	static int first_call = 1;
 
@@ -381,7 +388,7 @@ void net_init(void)
 		first_call = 0;
 	}
 
-	net_init_loop();
+	return net_init_loop();
 }
 
 /**********************************************************************/