If coreboot is configured to run the optionrom, keep the VESA framebuffer and use VESA mode 4117 (1024x768@16), coreboot initializes the eDP properly.

However, if coreboot is configured not to run the VGA optionrom and SeaBIOS is configured to run it, the eDP doesn't initialize properly. HDMI out works fine, but eDP doesn't from SeaBIOS.

I would prefer not to use SeaVGABIOS, but would rather want SeaBIOS to run the Intel VGA BIOS as SeaVGABIOS has issues with certain bootloaders and operating systems (even GRUB has a corrupt display with SeaVGABIOS in my testing).