[Bug 111475] Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111475

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #1 from Jani Nikula <jani.nikula at intel.com> ---
We don't look at the VBT active low bit, instead we read the backlight
registers and check what the BIOS has set up. This is due to historical
reasons, we always preferred what was actually set up by the BIOS instead of
looking at the VBT. Arguably this is a bug; if the BIOS does not set up the
registers, we don't get it right.

Does your BIOS enable the display?

Please set drm.debug=14 module parameter, and attach dmesg output all the way
from boot.

Please attach /sys/kernel/debug/dri/0/i915_vbt.

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