board: amlogic: vim3: configure serial# from ethaddr

The Khadas VIM3 and VIM3L boards, which are supported in Android via
Yukawa [1] need a serial number for usb/fastboot enumeration.

Whenever the environment does not provide a serial#, use the eth mac
address as serial#.

[1] https://source.android.com/setup/build/devices#vim3_and_vim3l_boards

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220119142400.127342-1-mkorpershoek@baylibre.com

board/amlogic/vim3/vim3.c

@@ -153,6 +153,7 @@ int misc_init_r(void)
 {
 	u8 mac_addr[MAC_ADDR_LEN];
 	char efuse_mac_addr[EFUSE_MAC_SIZE], tmp[3];
+	char serial_string[EFUSE_MAC_SIZE + 1];
 	ssize_t len;
 
 	if (!eth_env_get_enetaddr("ethaddr", mac_addr)) {
@@ -177,5 +178,13 @@ int misc_init_r(void)
 		eth_env_get_enetaddr("ethaddr", mac_addr);
 	}
 
+	if (!env_get("serial#")) {
+		eth_env_get_enetaddr("ethaddr", mac_addr);
+		sprintf(serial_string, "%02X%02X%02X%02X%02X%02X",
+			mac_addr[0], mac_addr[1], mac_addr[2],
+			mac_addr[3], mac_addr[4], mac_addr[5]);
+		env_set("serial#", serial_string);
+	}
+
 	return 0;
 }