I have recently put together a basic implementation of a vgabios for use with displays that are initialized by coreboot.
The idea is pretty simple - coreboot initializes the vga hardware and maps a framebuffer into an address in system memory. Then SeaVGABIOS implements the various legacy vga bios functions, but all it does with them is translate them to framebuffer updates. SeaVGABIOS doesn't try to initialize the display, change modes, or modify the vga registers.
This might be useful for those wishing to run fewer third-party blobs, for those where a vgabios isn't available at all, and for those wanting a faster boot (I've found proprietary vga bioses to be very slow).
I've run some basic tests on this version of SeaVGABIOS on my hardware. However, I don't have one of the boards where coreboot supports native vga init. It would be great if someone with the hardware (looks like stout, x60, and maybe others) could run tests.
To build this version of SeaVGABIOS, checkout the testing code from:
https://github.com/KevinOConnor/seabios/tree/testing
Then run "make menuconfig", turn on building for coreboot (CONFIG_COREBOOT), serial debugging (CONFIG_DEBUG_SERIAL), and enable the coreboot vgabios build (CONFIG_VGA_COREBOOT). The resulting vgabios will be in "out/vgabios.bin" - this file should be placed in CBFS in the file "vgaroms/vgabios.bin". Then launch coreboot with seabios as the payload (one can use the repo above to build seabios also, or use the normal coreboot method of building seabios). Ideally, the seabios menu should appear on the screen and basic OS boot loaders will work. But if not, the debugging info should help track down any problems.
-Kevin