Blank internal laptop screen from boot after kernel update 6.3.9->6.4.1

Internal laptop screen goes blank as soon as systemd boots from the intrd image with 6.4 kernel. Laptop has worked fine with all previous kernels to 6.3.9. Only error hint in the non-debug logs is "Cannot find any crtc or sizes". Laptop does boot into X behind the screen but has to be used blind. No joy connecting external monitors via DP or HDMI. Exact same problem booting into 6.4 with DRM-Tip.
System Architecture: x86-64
Kernel Versions: 6.4.1-arch1-1 and 6.4.0-1-drm-tip-git-g52c775d5fac7
Distro: Archlinux
Machine: Coffee Lake i7-8750H iGPU 630
Connector: eDP (and others)
Debug drm dmesg: http://ix.io/4zZO