REGRESSION: i915 Haswell 6 bpc dithering broken (watercolor color banding)

[Kareem Nedzmee-Seid]

i have a severe issue where haswell era graphics render colors
terribly on linux. the i915 driver seems to fail dithering on 6 bit
laptop displays, and colors get super washed out/banded because the
system treats it like an 8 bit panel when it's actually 6 bit. when
watching movies or videos, these jagged lines come out of nowhere and
ruin the image ;-;

i already have the patch file written by ville, but i don't know how
to safely compile a driver myself and i can't risk breaking anything
on this machine since i rely on it daily for schoolwork.

could the dev team please review and merge this patch into mainline
kernel / stable releases so it gets pushed out through official distro
updates? thank you! :)

original issue:
https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16045

here is original patch code as it is: