I sucessfully upgraded a RedmiAX6S from 23.05.2 to the new snapshot using the following method:
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
After this, and to double-check if a future upgrade would work fine, I've also flashed the new sysupgrade.itb image via LuCI, and again everything worked fine.
Once again thank you @981213 for the patch!!! 
Awesome! Glad to see that the Snapshots for Xiaomi AX3200 are available again.
Thank you for testing this!
It's also good to know that it will be compatible with future versions of OpenWrt.
Should we update somewhere for existing users that are already on 23.05.2 that they have to update using the factory.bin and this method instead of using the usual sysupgrade?
They'll trigger a warning if they attempt to use the sysupgrade image and it won't proceed. "SPI-NAND flash layout changes require bootloader update"
So it shouldn't be a problem unless they're running around clicking the force checkbox from the start. (In which case they'll get a non-bootable system until they follow the vendor recovery or reflash from serial input)
Thank you for the reply.
It's good that there is a safety check.
Perhaps we can also add the info on the Table of Hardware page when the official update releases:
https://openwrt.org/toh/xiaomi/ax3200
Including the guide on how to upgrade for existing installations only.
Question: is it possible to revert from the new layout (vendor u-boot chainloading mainline u-boot) to old layout (23.05.x with fixed-size kernel partition)?
I mean, I know I could revert back to factory firmware and install 23.05.x over the factory firmware, but I am wondering if there would be a simpler way to install 23.05.x over the new chained u-boots layout.
Using facinstall you can easily return to stock firmware. And using XMiR-Patcher you can install any OpenWRT on the stock firmware.
I can, of course, add support for the OpenWRT factory images to facinstall, but Iām too lazy (although such support may already be in my code, I need to check).
Thank you! Your work with facinstall and XMiR-Patcher is really great, thank you so much for your contributions!
In fact this makes it a lot easier to go back to factory and re-install 23.05.x.
Anyway I was wondering what would happen if I apply a 23.05.x sysupgrade.bin via sysupgrade command (or via LuCI). Since the new image has the kernel+rootfs in UBI format (sysupgrade.ubi), and the previous image has kernel in a fixed size partition and only rootfs in UBI (sysupgrade.bin), I am trying to discover if it would work or not (I know it can softbrick my device, that's I'm trying to confirm here).
I am asking this question both from my personal interest, but also to have a future official recommendation for users that would ask about downgrading from 24.xx to 23.05.xxx...
It seems like the image in the newly populated stable 23.05.3 download section still has the 5.15 kernel ("ARM64 OpenWrt Linux-5.15.15").
As expected. OpenWrt usually does not switch kernel versions within a stable release (23.05.2 -> 23.05.3 for example). Only kernel patches are applied on newer releases of a given stable version. A newer LTS kernel version (6.1) is already available in the snapshot releases for the AX6S as discussed above in this topic and it will be included in the next major stable release (24.x).
Ok, thanks for clearing things up.
Iāve got 3 AX6S setup as dumb APs. The in-place upgrade instructions worked on 2 of the APs.
I did not flash the 3rd one because itās tough to access, and the update process seems to wipe the config.
I tried updating the kernel using MTD write followed immediately by flashing an upgrade image with āforce keep configā and it still reset the config.
In the case of the two APs, I disconnected the APs from the network, attached to a laptop, SSHād in, installed and imported the old config and it got it back up and running.
Wondering if thereās another way to keep the config? If not, my 3rd Iāll have to wait until I can access it.
A main issue is that as a dumb AP, resetting the config introduces a second DHCP server on the network (and also my networkās IP range is not 192.168.1.X).
Great work on getting this done btw. Other than above, it was seamless.
Thank you all for the good info.
Just wanted to clarify, if we're currently on 23.05.2, we can upgrade to the upcoming 23.05.3 using sysupgrade as usual?
We don't need to use the mount and flash workaround for changing the partitions (as needed for the new snapshot)?
Correct. You can upgrade from 23.05.2 to 23.05.3 (when it gets released) without any special procedure, using sysugrade process as usual.
The instructions on this topic are applicable only to upgrade from 23.05.x to a snapshot build.
Awesome! Thank you so much for the confirmation
When I upgraded from 23.05.2 to snaphot via dd method, the configurations were kept, but when the device came up the configurations were all wrong (for example, it was showing 3 wifi radios instead of the expected 2 radios, and none was working).
I just reset the configurations and manually configured it from scratch. One thing I have not tried was to restore the configurarion from a previous backup to see if it would work.
Yah before the reboot the config was showing as correct. On the first AP, I saw it was correct and did a reboot (no sysupgrade). IP address etc reset when it was back up.
On the second AP I did a sysupgrade after the mtd method, checking ākeep configā on the upgrade on the second AP.
In both cases the reboot the IP changed to default so I assumed it was fully resetā¦. The config reload from backup definitely worked (which makes sense. Nothing /etc/config related would be impacted by this commit set).
Just wanted to confirm that I did a sysupgrade from 23.05.2 to the new 23.05.3 via the GUI Luci > System > Backup / Flash Firmware option and it upgraded successfully on Xiaomi AX3200 (EU).
No additional modifications were needed for this minor version and I've used the standard sysupgrade image from https://mirror-03.infra.openwrt.org/releases/23.05.3/targets/mediatek/mt7622/openwrt-23.05.3-mediatek-mt7622-xiaomi_redmi-router-ax6s-squashfs-sysupgrade.bin
I've chosen not to keep the previous configuration and setup everything from begining.
Please note that there seems to be an updated Luci > Network > DHCP and DNS menu in 23.05.3 that allows for multiple configurations:
I installed the latest snapshot (r25848-1ea6ddacc2) on my AX3200 (running 23.05.3 before).
The only unexpected bit was that I had to install luci via ssh before I could restore the config
Everything seems to be working fine, thanks all!
I assume this was not via sysupgrade method, right?
I used the same method as @remittor described: [mt7622] Re-enable Redmi AX6S/Xiaomi AX3200 snapshot builds - #4 by remittor
