[coreboot] No video output with Bay Trail

[Fred Young]

I have an Aaeon EMB-BT1 with an Intel Atom E3845 CPU. I've successfully built coreboot specifying "Bayley Bay CRB (FSP)" as the "Mainboard model".

When I boot the machine after programming the flash with coreboot, I see lots of output on the serial line including output indicating that SeaBIOS has started.

However, I don't see any output on the video display on either HDMI or VGA. Here are my .config settings relating to video/VGA:

CONFIG_VGA_BIOS_ID="8086,0f31"
CONFIG_ONBOARD_VGA_IS_PRIMARY=y
CONFIG_VGA_BIOS=y
CONFIG_VGA_BIOS_FILE="../intel/cpu/baytrail/vbios/Vga.dat"
CONFIG_VIDEO_MB=0
CONFIG_VGA_ROM_RUN=y

What do I need to do to get video output?