[Bug 105549] Black/blank screen at boot (last message line: fb: switching to inteldrmfb from EFI VGA) unless i915.modeset=0 is set

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105549

--- Comment #27 from Jani Nikula <jani.nikula at intel.com> ---
Okay, I have a hunch.

I assume you all 1) have a Dell Latitude 5490 or thereabouts, 2) you all have a
Kabylake (KBL) system with either Sunrisepoint PCH (SPT) or Kabylake PCH (KBP),
and 3) the problems started after updating the BIOS.

Please check your dmesg with drm.debug=14 set, and look for lines similar to
these:

[   35.431169] [drm:intel_pch_type [i915]] Found SunrisePoint LP PCH
[   35.456889] i915 device info: pciid=0x5917 rev=0x07 platform=KABYLAKE gen=9

There are KBL systems with SPT and KBP, but there are *also* newer KBL systems
with Cannonlake PCH (CPT). The way the VBT is specified, we need to do some
mapping on the DDC pin on CPT. The mapping would be right for CPT, but wrong
for SPT and KBP.

Now, I presume Dell has inadvertently based their BIOS update on the newer
model's BIOS, without taking this into account.

It would really be useful to get the VBT dumps before and after BIOS update.
Can you downgrade the BIOS?

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