x86: Boot failure on select chromebooks with v6.15-rc5

[Vignesh Raman]

Hi,

With v6.15-rc5, the below chromebooks were not booting with the 
following message. These tests were run in drm-ci.

Starting kernel ...
[    1.843801]  ? __pfx_kernel_init+0x10/0x10
[    1.909838]  ? __pfx_kernel_init+0x10/0x10

https://gitlab.freedesktop.org/vigneshraman/linux/-/pipelines/1420485

Failing jobs:
amdgpu:stoney (AMD Stoney Ridge chipset): 
https://gitlab.freedesktop.org/vigneshraman/linux/-/jobs/76000926

i915:amly (64 bit Intel Whiskey Lake): 
https://gitlab.freedesktop.org/vigneshraman/linux/-/jobs/76000929

i915:whl (64 bit Intel Amber Lake): 
https://gitlab.freedesktop.org/vigneshraman/linux/-/jobs/76000931

These tests were passing till v6.14-rc7, and the issue was seen starting 
in v6.15-rc1. This issue is seen only with these 3 boards and does not 
affect other chromebooks (the pipeline log shows the other i915 driver 
tests).

On bisecting the commits, the commit which introduced this issue is,
3181424aeac2f6596534bf43021a10eae294a9b0 x86/early_printk: Add support 
for MMIO-based UARTs

After reverting the below commits in v6.15-rc5, the board boots and 
tests are executed:
3181424aeac2 x86/early_printk: Add support for MMIO-based UARTs
996457176bb7 x86/early_printk: Use 'mmio32' for consistency, fix 
comments (this fixes 3181424aeac2)

pipeline after reverting the commits,
https://gitlab.freedesktop.org/vigneshraman/linux/-/pipelines/1420493

Please could you look into this issue. Thank you.

Regards,
Vignesh