ramips: allow to set switchdev by board in ramips_set_preinit_iface

This adds the option to determine switchdev by board when setting
preinit iface for failsafe. The patch reorganizes the code to use
functions for setting correct switchdev based on SOC and board,
which is supposed to improve readability and maintainability.

In this patch, the ramips_switchdev_from_board function is added
without specifying an actual device using it. This is meant to
make the life of device supporters waiting for merge easier, as
there is less to rebase and keep track of.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/base-files/lib/preinit/07_set_preinit_iface_ramips

@@ -3,27 +3,54 @@
 # Copyright (C) 2013 OpenWrt.org
 #
 
-ramips_set_preinit_iface() {
-	RT3X5X=$(grep -E "(RT3.5|RT5350|MT7628|MT7688|MT7620|MT7621)" /proc/cpuinfo)
+. /lib/functions.sh
 
-	if [ -n "${RT3X5X}" ]; then
-		# The ethernet switch driver enables VLAN by default, but
-		# failsafe uses eth0, making the device unreachable:
-		# https://dev.openwrt.org/ticket/18768
-		case "${RT3X5X}" in
-		*MT7620*)
-			ralink_switchdev=mt7620
-			;;
-		*MT7621*)
-			ralink_switchdev=mt7530
-			;;
-		*)
-			ralink_switchdev=rt305x
-			;;
-		esac
-		swconfig dev $ralink_switchdev set reset 1
-		swconfig dev $ralink_switchdev set enable_vlan 0
-		swconfig dev $ralink_switchdev set apply 1
+ramips_switchdev_from_soc() {
+	# The ethernet switch driver enables VLAN by default, but
+	# failsafe uses eth0, making the device unreachable:
+	# https://dev.openwrt.org/ticket/18768
+
+	local switchdev
+	local RT3X5X=$(grep -E "(RT3.5|RT5350|MT7628|MT7688|MT7620|MT7621)" /proc/cpuinfo)
+
+	[ -n "$RT3X5X" ] || return 1
+
+	case "$RT3X5X" in
+	*MT7620*)
+		switchdev=mt7620
+		;;
+	*MT7621*)
+		switchdev=mt7530
+		;;
+	*)
+		switchdev=rt305x
+		;;
+	esac
+
+	echo "$switchdev"
+}
+
+ramips_switchdev_from_board() {
+	# For these devices, external ethernet switch should be used
+	# instead of the SoC internal switch.
+
+	local switchdev
+	local board=$(board_name)
+
+	case "$board" in
+	esac
+
+	echo "$switchdev"
+}
+
+ramips_set_preinit_iface() {
+	local switchdev=$(ramips_switchdev_from_board)
+	[ -n "$switchdev" ] || switchdev=$(ramips_switchdev_from_soc)
+
+	if [ -n "$switchdev" ]; then
+		swconfig dev $switchdev set reset 1
+		swconfig dev $switchdev set enable_vlan 0
+		swconfig dev $switchdev set apply 1
 	fi
 
 	ifname=eth0