Boot fail with UBIFS_FS=y on Qualcomm msm8974/msm8226

[Luca Weiss]

Hey all,

sometime last year (June 2021?) I first noticed that with arm32 qcom_defconfig 
under some circumstances I get weird boot failures on msm8974-fairphone-fp2, 
and lately also seeing similar with apq8026-lg-lenok.

In short, with CONFIG_UBIFS_FS=y there's nothing from serial console, nothing 
from earlycon, just nothing on serial at all. As soon as I disable this config 
option and rebuild it boots up fine again.

At some point I also got this from fp2 logs, after I changed something in the 
boot procedure (maybe fastboot boot instead of fastboot flash? I don't recall)

> Error: invalid dtb and unrecognized/unsupported machine ID
>   r1=0x00000000, r2=0x00000000
> Available machine support:
> 
> ID (hex)        NAME
> ffffffff        Generic DT based system
> 
> Please check your kernel config and/or bootloader.

With CONFIG_UBIFS_FS=m and loading the module at runtime seems to work fine (at 
least nothing visibly broke) although I didn't try mounting anything with that 
file system.

Does anyone maybe have an idea what might cause this and/or how to debug this? 
While just disabling UBIFS_FS in my config solves the issue I feel like this 
should be resolved, because I also sometimes forget that I have to disable 
this from qcom_defconfig and then wonder why my boards aren't booting.

Regards
Luca