[Bug 108225] [LPT SPT KBP] Acer V3-772G screen brightness cannot be adjusted with i915.fastboot enabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108225

--- Comment #33 from Tolga Cakir <cevelnet at gmail.com> ---
(In reply to Hans de Goede from comment #29)
> About the short flicker, I've been tracking down a regression in 4.20 (and
> thus also drm-next) which causes the screen to briefly go purple with DSI
> panels.
> 
> Can you try:
> 
> git revert 516a49cc19467e298d08a404f73a6e311f4548d1
> 
> That fixes the purple flash for me (I need to write a proper commit message
> and then submit this revert upstream for 4.20).

(In reply to Maarten Lankhorst from comment #31)
> Created attachment 142522 [details] [review]
> More debug spam
> 
> Can you take a look at this patch?

Thanks for the suggestions and the patch! I have applied git revert
516a49cc19467e298d08a404f73a6e311f4548d1, aswell as the patch from comment #31.
The flickering is gone. I have flicker-free, blanking-free boot experience.
Backlight never turns off during boot and backlight controls work after boot
procedure. Just perfect!

The debug message from patch #31 gave me this:
[    2.426812] [drm] Backlight PCH value: 861, converted to freq 1134,
converted to lpt units 930, minmax: 249/4882

To sum it up: git revert 516a49cc19467e298d08a404f73a6e311f4548d1 and applying
patch #31 fixes this issue! Thank you! I haven't applied the 2nd git revert, as
this already worked as I wished.

Cheers,
Tolga

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