[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 #22 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to Tolga Cakir from comment #21)
> I have exactly the same issue on the Dell M3800 (Intel i7-4702HQ + muxless
> Nvidia K1100M). Using i915.fastboot=1, I don't see a single flicker from
> power-on all the way to GNOME desktop. However, just as reported, backlight
> control doesn't work and is set to maximum. I have additionally tried
> acpi_backlight=[vendor,native,video] without any success.
> 
> I can test patches and provide further debug infos, if needed. Please let me
> know.

Do you have LynxPoint (LPT) PCH? Look for something like this in the dmesg:

[    5.224781] [drm:intel_pch_type [i915]] Found LynxPoint PCH

Does the trick from comment #12 help? What's the output of the intel_reg reads
in the two scenarios? (See comment #13 for example.)

I just want to ensure you are really experiencing the same bug, and not
something else.

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