coreboot

I have a X230 with a eDP panel (LP125WF4-SPB1). My FHD mod board is self designed but somewhat similar to the nitrocaster mod (just much simpler). It takes DP_D from the docking port (2 lanes plus AUX plus HDP) and BACKLIGHT_ON + PANEL_BKLT_CTRL from the LVDS connector and connects everything directly to the eDP panel. It is totally passive and has no MCU and no EEPROM. I also attached the schematic (dasher-fhd.pdf).

The panel stays blank until Linux boots and from the debug output it seems libgfxinit does not detect it at all. Once drm/i915 in Linux takes over the panel starts up and works perfectly fine including backlight control. From the log it seems that coreboot/libgfxinit for some reason can't read the EDID but Linux has no problem reading the EDID. An external display attached to the mini-DP port is detected by libgfxinit and does work with coreboot.

I'm using coreboot 25.03 with "ThinkPad X230 eDP Mod (2K/FHD)" as mainboard and libgfxinit with linear framebuffer and edk2 payload. Though I also tried other payloads, gfx initialization settings, various changes to gma-mainboard.ads, devicetree.cb and other hacks I though worth a try. I also played around a lot with modifications to the VBT (explicitly configuring my panel including DTD, enabling edidless, ...). But nothing made any difference.

Attached you find a coreboot log with Ada debug enabled (cbmem.log) and a full Linux boot log with drm.debug=0x1ff (linux.log) from the same boot since I though it might help to see what i915 is doing to get the panel working.