net: moxa: MAC address reading, generating, validity checking

This device does not remember its MAC address, so add a possibility
to get it from the platform. If it fails, generate a random address.
This will provide a MAC address early during boot without user space
being involved.

Also remove extra calls to is_valid_ether_addr().

Made after suggestions by Andrew Lunn:
1) Use eth_hw_addr_random() to assign a random MAC address during probe.
2) Remove is_valid_ether_addr() from moxart_mac_open()
3) Add a call to platform_get_ethdev_address() during probe
4) Remove is_valid_ether_addr() from moxart_set_mac_address(). The core does this

v1 -> v2:
Handle EPROBE_DEFER returned from platform_get_ethdev_address().
Move MAC reading code to the beginning of the probe function.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Suggested-by: Andrew Lunn <andrew@lunn.ch>
CC: Yang Yingliang <yangyingliang@huawei.com>
CC: Pavel Skripkin <paskripkin@gmail.com>
CC: Guobin Huang <huangguobin4@huawei.com>
CC: Yang Wei <yang.wei9@zte.com.cn>
CC: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20220818092317.529557-1-saproj@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/moxa/moxart_ether.c

@@ -62,9 +62,6 @@ static int moxart_set_mac_address(struct net_device *ndev, void *addr)
 {
 	struct sockaddr *address = addr;
 
-	if (!is_valid_ether_addr(address->sa_data))
-		return -EADDRNOTAVAIL;
-
 	eth_hw_addr_set(ndev, address->sa_data);
 	moxart_update_mac_address(ndev);
 
@@ -172,9 +169,6 @@ static int moxart_mac_open(struct net_device *ndev)
 {
 	struct moxart_mac_priv_t *priv = netdev_priv(ndev);
 
-	if (!is_valid_ether_addr(ndev->dev_addr))
-		return -EADDRNOTAVAIL;
-
 	napi_enable(&priv->napi);
 
 	moxart_mac_reset(ndev);
@@ -488,6 +482,13 @@ static int moxart_mac_probe(struct platform_device *pdev)
 	}
 	ndev->base_addr = res->start;
 
+	ret = platform_get_ethdev_address(p_dev, ndev);
+	if (ret == -EPROBE_DEFER)
+		goto init_fail;
+	if (ret)
+		eth_hw_addr_random(ndev);
+	moxart_update_mac_address(ndev);
+
 	spin_lock_init(&priv->txlock);
 
 	priv->tx_buf_size = TX_BUF_SIZE;