When i915kms.ko is loaded, no matter whether it is the one from the base system (/boot/kernel/i915kms.ko) or from the drm-legacy-kmod (version g20190109) port (/boot/modules/i915kms.ko), the system consoles can no more be seen. Apart from the display problem, the consoles remain functional. Text input is still possible.
The error may be caused by either i915kms.ko or /boot/kernel/drm2.ko, which seems to be loaded automatically with i915kms.ko.
When i915kms.ko is loaded manually from the console, the screen gets black. When it is loaded automatically on xinit, the console is hidden anyway. Switching to the console with ctrl-alt-F1/F2... leads to a distorted screen. Switching back to X works properly. When X terminates, the screen gets black.
GPU is Intel Haswell 4600 (part of Intel Core i7-4790S CPU).
See my comments in #217689 for further details. As opposed to the classification of that previous bug, the issue is not X11 related, as it can be observed without X11 as well.
When in doubt try,
# pkg delete drm-kmod-legacy
# pkg delete xf86-video-intel
# pkg install drm-kmod
Move away stuff that could cause issues
# mv /boot/kernel/drm.ko /root/
# mv /boot/kernel/drm2.ko /root/
# mv /boot/kernel/i915kms.ko /root/
# mv /etc/X11/xorg.conf /root/xorg.conf
# mv /etc/X11/xorg.d /root/
Clear any module loading and sysctl entries for graphics drivers from /boot/loader.conf and /etc/rc.conf.
Disconnect external/multiple displays
# kldload i915kms
# kldstat -v (confirm that drm.ko and i915kms.ko are loaded from /boot/modules)
Haswell is definitely supported by the new drivers and a default, empty configuration should be sufficient to have functional X and VTs. In most cases, the error is due to conflicts with existing older drm drivers, intel ddx or misconfiguration.
If this still doesn't work we need to troubleshoot further. Maybe some quirks with that specific GPU?