ZBT-Z8103AX bricked after sysupgrade - UBI recovery required

Installing and Using OpenWrt
1

:sos_button: HELP: ZBT-Z8103AX Won't Boot After Sysupgrade - Recovery Needed

  • Device: ZBT-Z8103AX (MT7981)

  • Issue: Sysupgrade between custom OpenWrt 24.10.2 builds → won't boot

  • Status: NOT bricked (U-Boot works, InitRAMFS boots fine)

  • Need: How to recover persistent boot capability

What's Happening


ubi0 error: vtbl_check: too large reserved_pebs 751, good PEBs 512

UBI error: cannot attach mtd4

Kernel panic - not syncing: VFS: Unable to mount root fs

Root cause: U-Boot creates UBI volumes expecting 916 PEBs, but Linux only sees 512 PEBs available.

What Works :white_check_mark:

  • U-Boot console access

  • InitRAMFS boots perfectly (all hardware functional)

  • TFTP/Ymodem file transfers

  • Original device with different build works fine

What I Need :sos_button:

Any working solution to get persistent firmware booting again.

Specific Questions:

  1. Boot parameters: How to force Linux to see full UBI partition size?

  2. UBI rebuild: Commands to recreate volumes within 512 PEB limit?

  3. Compatible firmware: Anyone have working custom ZBT-Z8103AX build?

  4. Recovery method: Alternative approach that bypasses this issue?

Failed Attempts :cross_mark:

  • Various ubi.mtd= boot parameters

  • Complete MTD erase and recreation

  • Factory firmware → same issue

  • U-Boot environment changes

Quick Details


U-Boot partition: mtd6, 114 MiB, 916 PEBs ← Works

Linux partition: mtd4, 64 MiB, 512 PEBs ← Fails

Help Appreciated

  • ZBT-Z8103AX users: Seen this before? How did you fix it?

  • OpenWrt devs: Standard way to handle UBI volume table mismatches?

  • Anyone: Even hacky workarounds welcome!

Have serial console access and can test any suggestions. Device is recoverable - just need the right approach.

Quick responses much appreciated! :folded_hands:

2

Waay too much (AI ?) text in the post, TLDR.

recreate the original layout from within the initramfs, attempt to flash again, afterwards.

3

Thanks for the reply! Sorry for the long post, Made it short. I have tried recreating original layout within initramfs, at certain point that is failing. Let me try again and get back here.

4

The layout Openwrt expects is in the PR -
https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/mediatek/dts/mt7981b-zbtlink-zbt-z8103ax.dts;h=2b079f5bcac6afb143329bc81d69826ac393a171;hb=4300bc668819a77226b6e8ea079d3067f216e7bb

5

Thanks @frollic for the dts. Finally found the issue. The ubi partition is having a different address range. This would the correct partition.

   partition@580000 {
                            label = "ubi";
                            reg = <0x580000 0x7280000>;
                    };

This needs to be patched.