[Bug 108773] i915.fastboot=1 is broken on Thinkpad S1 Yoga (Haswell)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108773

--- Comment #12 from Johannes Krampf <johannes.krampf at gmail.com> ---
Created attachment 144307
  --> https://bugs.freedesktop.org/attachment.cgi?id=144307&action=edit
dmesg linux-next 20190517 with fastboot on T440s

I tried linux-next. When I cloned the tree, the latest version was
b1d6682ef9bb6893690e39e2186371a1dc45072b with the tag next-20190517.

The kernel worked fine without fastboot.

With fastboot I would very briefly (<second) see boot messages, then the screen
would go black, but with the backlight on. Finally, around the time I expect
Wayland to have started, the screen went completely black with the backlight
being off.

The machine was running and I was able to open a terminal and redirect dmesg to
a file. I was also able to switch to a virtual terminal, redirect dmesg once
more to a file and to trigger a reboot. All of this was with the backlight
being off.

I did not try the equivalent of `xset dpms force off` because I couldn't
remember how this worked on Wayland/sway. I can try this if it would be
helpful. Please ask me in this case.

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