bcm27xx: base-files: diag: improve LEDs behaviour

As reported in https://github.com/openwrt/openwrt/issues/15834 using the PWR
LED for indicating diag status is confusing since this is usually used for
power supply failures on RPi devices.
This commit uses ACT LED for diag status and restores it to mmc activity.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/bcm27xx/base-files/etc/diag.sh

@@ -5,11 +5,23 @@
 . /lib/functions.sh
 . /lib/functions/leds.sh
 
+status_led_restore_trigger() {
+	local led_lc=$(echo "$status_led" | awk '{print tolower($0)}')
+	local led_path="/proc/device-tree/leds/led-$led_lc"
+	local led_trigger
+
+	[ -d "$led_path" ] && \
+		led_trigger=$(cat "$led_path/linux,default-trigger" 2>/dev/null)
+
+	[ -n "$led_trigger" ] && \
+		led_set_attr $status_led "trigger" "$led_trigger"
+}
+
 set_state() {
-	if [ -d "/sys/class/leds/PWR" ]; then
-		status_led="PWR"
-	else
+	if [ -d "/sys/class/leds/ACT" ]; then
 		status_led="ACT"
+	else
+		return
 	fi
 
 	case "$1" in
@@ -22,11 +34,11 @@ set_state() {
 	preinit_regular)
 		status_led_blink_preinit_regular
 		;;
-        upgrade)
-                status_led_blink_preinit_regular
-                ;;
+	upgrade)
+		status_led_blink_preinit_regular
+		;;
 	done)
-		status_led_on
+		status_led_restore_trigger
 		;;
 	esac
 }