Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!
Is a driver, which is written in a high level language and open source implementation to initialize the graphics hardware on a platform. It might implement only a subset of possible resolution, a subset of possible color depth and work only on a subset of available connectors.
Even though coreboot can run VGA Option ROMs, those aren't called native graphics init.
Usually the full color depth and native screen resolution is used. If (x86) VGA hardware is present, one can not assume that it has been initialized at all. A payload should either initialize the GPU on its own or use coreboot tables to gather information about the current state. The payload can not determine if the information provided in coreboot tables is still valid. A bootloader might have changed the GPUs current state.
libgfxinit is a graphics initialization (aka modesetting) library for embedded environments. It currently supports only Intel hardware, more specifically the Intel Core processor line.
It can query and set up most kinds of displays based on their EDID information. You can, however, also specify particular mode lines.
libgfxinit is written in SPARK, an Ada subset with formal verifica- tion aspects. Absence of runtime errors can be proved automatically with SPARK GPL 2016.
Note: You have to compile the coreboot toolchain with ADA support to use libgfxinit !
On some pre Haswell Intel platforms the graphics can be initialized using C code, but only on the internal LVDS connector.
Note: For some platforms this can be worked around. See Video Bios Tables for more information.
Some payload and OS might not work at all, as they depend on resolution switching or text mode. Those cannot be fixed. You have to use a proper VGA option ROM.
If you find a software that doesn't work well, you can try to parse the coreboot tables to find the graphics mode or framebuffer in use. List of software that is already aware of coreboot's framebuffer: