ath79: mikrotik: erase firmware on SPI NOR before install

On Mikrotik SPI NOR devices, the firmware partition must be erased when
flashing from stock firmware, otherwise leftover bits (in particular a
kernel signature) can trigger a boot loop.

When booted from initramfs (the only way to install OpenWRT on these
devices), this patch unconditionally erases the firmware partition in
the do_upgrade() stage for all supported SPI NOR devices.

This is forward-ported from ed49d0876 and 20452a8db

Signed-off-by: Thibaut VARÈNE <[email protected]>

target/linux/ath79/mikrotik/base-files/lib/upgrade/platform.sh

@@ -38,6 +38,9 @@ platform_do_upgrade() {
 		platform_do_upgrade_mikrotik_nand "$1"
 		;;
 	*)
+		# NOR devices: erase firmware if booted from initramfs
+		[ -z "$(rootfs_type)" ] && mtd erase firmware
+
 		default_do_upgrade "$1"
 		;;
 	esac