[REGRESSION] Dell Latitude 7390 Intel UHD 620 screen becomes extremely dim after kernel 7.x upgrade

Hello Linux kernel and Intel graphics developers,

I would like to report a kernel regression affecting the internal display
brightness on my Dell Latitude 7390 laptop.

After upgrading from Linux kernel 6.14.x to Linux kernel 7.x, the internal
laptop display becomes extremely dim immediately after boot.

The system continues to run normally, but the brightness level becomes
almost unusable.

Booting back into Linux kernel 6.14.x restores normal display brightness.

Hardware information:

Laptop:
Dell Latitude 7390

CPU:
Intel Core i7-8650U

GPU:
Intel UHD Graphics 620
PCI ID: 8086:5917

Graphics driver:
i915

Display:
Chi Mei Innolux 1920x1080 eDP panel

BIOS:
Dell version 1.44.0

Operating systems tested:

   -

   Ubuntu 24.04.4 LTS
   -

   Linux Mint 22.2 (based on Ubuntu 24.04)

The same issue happens on both distributions.

Working kernel:
6.14.0-29-generic

Problematic kernel:
7.x

Steps to reproduce:

   1.

   Install Ubuntu 24.04 or Linux Mint 22.2.
   2.

   Update the system to kernel 7.x.
   3.

   Reboot.
   4.

   The internal display becomes extremely dim.
   5.

   Boot kernel 6.14.x.
   6.

   Display brightness works normally again.

Additional information:

   -

   Secure Boot is disabled.
   -

   The issue is reproducible.
   -

   The system remains usable except for the display brightness problem.
   -

   The regression appears between kernel 6.14 and kernel 7.x.
   -

   The graphics driver in use is Intel i915.

This may be related to Intel i915 backlight handling or eDP panel
initialization.

I can provide dmesg logs and additional debugging information if required.

Thank you for your help.

Best regards,
PoL