dm: eth: Add support for ethprime env var

The ethprime env var is used to indicate the starting device if none is
specified in ethact. Also support aliases specified in the ethprime var.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/net/eth.c b/net/eth.c
index a2e6f34..b6c2af3 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -360,6 +360,18 @@
 		printf("No ethernet found.\n");
 		bootstage_error(BOOTSTAGE_ID_NET_ETH_START);
 	} else {
+		char *ethprime = getenv("ethprime");
+		struct udevice *prime_dev = NULL;
+
+		if (ethprime)
+			prime_dev = eth_get_dev_by_name(ethprime);
+		if (prime_dev) {
+			eth_set_dev(prime_dev);
+			eth_current_changed();
+		} else {
+			eth_set_dev(NULL);
+		}
+
 		bootstage_mark(BOOTSTAGE_ID_NET_ETH_INIT);
 		do {
 			if (num_devices)
@@ -367,6 +379,9 @@
 
 			printf("eth%d: %s", dev->seq, dev->name);
 
+			if (ethprime && dev == prime_dev)
+				printf(" [PRIME]");
+
 			eth_write_hwaddr(dev);
 
 			uclass_next_device(&dev);
@@ -915,8 +930,20 @@
 		act = getenv("ethact");
 		env_changed_id = env_id;
 	}
-	if (act != NULL)
+
+	if (act == NULL) {
+		char *ethprime = getenv("ethprime");
+		void *dev = NULL;
+
+		if (ethprime)
+			dev = eth_get_dev_by_name(ethprime);
+		if (dev)
+			eth_set_dev(dev);
+		else
+			eth_set_dev(NULL);
+	} else {
 		eth_set_dev(eth_get_dev_by_name(act));
+	}
 
 	eth_current_changed();
 }