Created attachment 143205 [details]
4.19.0 Debian kernal boot log (external screen working)

I can reproduce this with

    00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Carrizo (rev c4)
    03:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Bonaire
XT [Radeon R9 M280X] (rev 80)

on a “Lenovo ideapad Y700-ACZ”.

When I boot into the released Linux 4.19.0 from Debian I get a blank screen,
however today I discovered that if you have an external displayed plugged
during boot-up that display will be successfully enabled and you can then log
in as usual. The internal laptop display will not ever be enabled however and
checking under *Systemsettings* → *Monitor Settings* (KDE) will not show it
either. Also the entire system will feel very sluggish (not CPU or disk
related, I checked) and is only usable with lots of patience. On shutdown the
system will then hang (nothing about this in system logs unfortunately).