[Lenovo P11] keyman91:
Bootloader must be unlocked before flashing the original firmware provided on page 1 (TB138FC_CN_OPEN_USER_Q00024.0_S_ZUI_14.0.625_ST_220901_qpst) otherwise you will enter into a soft brick!​

Bootloader unlocking - Easy method​

The easiest way to unlock the bootloader is to go to Developer Tools and click OEM Unlock. This will allow you to unlock the bootloader via the fastboot command fastboot flashing unlock.

Bootloader unlocking - Longer method​

If you are like me and did not know this and you flashed the original firmware before unlocking the bootloader, you will enter into an infinite bootloop that will keep bringing you back to the bootloader.

You will not be able to boot into anything from here such as the system or recovery mode. And because we never allowed OEM unlock via Developer Tools, any fastboot commands to flash or unlock will result in command failures.

What we need to do in this case is to request for an unlock file from the Lenovo ZUI website here:

ZUI官网 - 解锁

Use Google Chrome to translate the website if you are not Chinese and cannot read the text.

Spoiler content hidden.

Please note, you must create an account and be logged in in order to submit a request. There are a limited number of requests per day that the Lenovo ZUI website will fulfill so you may get a red error text saying "too many requests have been made already". If this happens, then you will need to try again the next day. (Best to try at 00:00 Beijing time).

If you successfully submitted the request, you will get a popup saying your unlock file will be sent to you soon via email. The only problem is that the email never comes. My theory is that the request gets queued in their backend servers where an automation will run which will create and sign the unlock file but the email notification component is buggy or broken. Anyways, if you try the following link 1-2 hours later, you should be able to download your personal unlock file (replace the {serialNumber} field with yours):

http://cdn.zui.lenovomm.com/developer/tabletboot/{serialNumber}/sn.img

This unlock file is unique to your tablet's serial number so unfortunately it cannot be shared by another person. If you try anyone else's sn.img file, you will get a serial mismatch error.

Once you have the unlock file, you need to issue the following commands in fastboot which unlock the bootloader:

fastboot flash unlock sn.img
fastboot oem unlock-go

Tablet recovery now that bootloader is unlocked​

Enter EDL mode by:

Powering off the tablet

Holding Volume Up as you plug the USB in

Reflash the original firmware via QFIL

It should boot you back into fastboot mode after flashing

You might enter a bootloop at the Lenovo logo, if this happens, just wait a few minutes. After a few bootloops, it will eventually kick you back out into fastboot mode

At this stage, you are either lucky like a few members on this forum where all you needed to do was issue the following command to boot:

fastboot --set-active=a
fastboot reboot

Or you are unlucky like me where this will not work and you are still in an infinite bootloop. If this is the case:

Grab the image files from the original ROM (TB138FC_CN_OPEN_USER_Q00024.0_S_ZUI_14.0.625_ST_220901_qpst\image) and flash them all one-by-one via fastboot:

fastboot flash boot boot.img
fastboot flash dtbo dtbo.img
fastboot flash metadata metadata.img
fastboot flash persist persist.img
fastboot flash recovery recovery.img
fastboot flash vbmeta vbmeta.img
fastboot flash vbmeta_system vbmeta_system.img

Then you can reboot into recovery which will automatically factory reset the tablet and reboot you into the system.

fastboot reboot recovery