I've built the current 5.7.14 kernel and am running into an issue on my Brasswel (N3150) and CherryTrail (Atom x5-Z8350) systems. The former runs an old Ubuntu 14.04.6LTS system, the latter runs Devuan Beowulf (off an external drive).
The greeter (SDDM) seems to work fine but gives me a black screen with just the mouse cursor when I 1) login or 2) click the session selector.
I have a hunch this has to do with the compositor or OpenGL more in general: hitting Shift-Alt-F12 in KDE Plasma to disable KWin's compositor gives me back at least a part of the image.
Both systems work fine with the 4.19.118 kernel; the Devuan install also works fine with 5.7.14 on an HP laptop with an i3 CPU that's a few years old now.
I haven't found anything relevant; testing with i915 powersaving, fastboot and experimental hw support didn't help me solve the problem. Any idea what I can try short of building a 5.6 kernel in hope it'll work properly?
(installing Devuan's own kernels will force me to install apparmor which I'd prefer to avoid.)