mediatek: mt7622: add a second u-boot for redmi-ax6s

The vendor u-boot knows nothing about UBI, and we used to have a
fixed-size kernel partition for vendor u-boot and UBI for rootfs.
However, that fixed partition becomes too small eventually, and
expanding it requires complicated procedure.

This commit changed the flash layout and added a second u-boot
where the kernel supposed to be.
Now the vendor u-boot chainloads our mainline u-boot, and our
u-boot reads kernel+rootfs from UBI, verifies it, and boot
into OpenWrt.

There are two possible ways to convert from the old fw:
Flash the factory image using mtd (provided by @rany2):

mount -o remount,ro /
mount -o remount,ro /overlay
cd /tmp
dd if=factory.bin bs=1M count=4 | mtd write - kernel
dd if=factory.bin bs=1M skip=4 | mtd -r write - ubi

Or, flash the 2nd u-boot via mtd and upload the firmware
to the 2nd u-boot using tftp:

1. prepare a tftp server at 192.168.1.254 to serve the
   sysupgrade image:
   openwrt-mediatek-mt7622-xiaomi_redmi-router-ax6s-squashfs-sysupgrade.itb
2. upload the ubi-loader.itb to OpenWrt /tmp, and flash it to
   the old kernel partition:
   mtd -r write openwrt-mediatek-mt7622-xiaomi_redmi-router-ax6s-ubi-loader.itb
3. The router should reboot and flash the sysupgrade image via TFTP.

Procedure for flashing from vendor firmware shouldn't change.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

2 files changed, 6 insertions, 6 deletions

diff --git a/target/linux/mediatek/mt7622/base-files/etc/uci-defaults/05_fix-compat-version b/target/linux/mediatek/mt7622/base-files/etc/uci-defaults/05_fix-compat-version
index 6309728e4b..dd224f3d8c 100644
--- a/target/linux/mediatek/mt7622/base-files/etc/uci-defaults/05_fix-compat-version
+++ b/target/linux/mediatek/mt7622/base-files/etc/uci-defaults/05_fix-compat-version
@@ -9,7 +9,8 @@ case "$(board_name)" in
 	uci set system.@system[0].compat_version="1.1"
 	uci commit system
 	;;
-	linksys,e8450-ubi)
+	linksys,e8450-ubi|\
+	xiaomi,redmi-router-ax6s)
 	uci set system.@system[0].compat_version="2.0"
 	uci commit system
 	;;
diff --git a/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh b/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
index 236e8fdfb0..59375ccd9b 100755
--- a/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
+++ b/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
@@ -10,7 +10,8 @@ platform_do_upgrade() {
 	linksys,e8450-ubi|\
 	ubnt,unifi-6-lr-v1-ubootmod|\
 	ubnt,unifi-6-lr-v2-ubootmod|\
-	ubnt,unifi-6-lr-v3-ubootmod)
+	ubnt,unifi-6-lr-v3-ubootmod|\
+	xiaomi,redmi-router-ax6s)
 		[ -e /dev/fit0 ] && fitblk /dev/fit0
 		[ -e /dev/fitrw ] && fitblk /dev/fitrw
 		bootdev="$(fitblk_get_bootdev)"
@@ -48,8 +49,7 @@ platform_do_upgrade() {
 	elecom,wrc-x3200gst3|\
 	mediatek,mt7622-rfb1-ubi|\
 	netgear,wax206|\
-	totolink,a8000ru|\
-	xiaomi,redmi-router-ax6s)
+	totolink,a8000ru)
 		nand_do_upgrade "$1"
 		;;
 	linksys,e8450)
@@ -84,8 +84,7 @@ platform_check_image() {
 	elecom,wrc-x3200gst3|\
 	mediatek,mt7622-rfb1-ubi|\
 	netgear,wax206|\
-	totolink,a8000ru|\
-	xiaomi,redmi-router-ax6s)
+	totolink,a8000ru)
 		nand_do_platform_check "$board" "$1"
 		return $?
 		;;