U-Boot payload

Return to previous index

Libreboot has experimental support for using U-Boot as a coreboot payload since the 20221214 release. Refer to docs/hardware/ for a complete list of U-Boot targets in Libreboot.

U-Boot integration in Libreboot is currently at a proof-of-concept stage, with most boards completely untested and most likely not working. ROM images for them are mostly intended for further testing and development. If you have one of these machines and want to help fix things, you can ping alpernebbi on Libera IRC, who ported these boards to Libreboot.

As of 14 December 2022, building of U-Boot images has been tested on Debian. Make sure you have the latest lbmk from the Git repository, and the build dependencies are installed like so, from lbmk/ as root:

./build dependencies debian

This installs everything needed for ./build roms, and part of the build process makes use of coreboot’s own cross-compile toolchain.

QEMU x86/ARM64 virtual machines are also supported, which should be easy targets to start tinkering on if you want to contribute.

Usage

When your board is powered on, U-Boot will ideally turn on the display and start printing console messages there. After a countdown of a few seconds it will proceed to automatically boot whatever it can find. U-Boot will fall back to an interactive prompt if its boot sequence fails or if you interrupt the countdown.

U-Boot supports UEFI to some extent, enough to run a GRUB package that would be installed by whatever OS you want to have on your device. The boot sequence checks for the standard UEFI removable media paths like /efi/boot/bootaa64.efi, so you should be able to use your desired OS’ generic installer images. For details, see upstream documentation for UEFI on U-Boot.

Otherwise, the boot sequence also checks an extlinux.conf file that can configure which kernel, initramfs, device-tree file and kernel command line arguments should be used. See upstream documentation for Generic Distro Configuration Concept.

If you want to work inside the U-Boot shell, see an incomplete list of shell commands, or use the help command inside the prompt. Configuration is done via environment variables inside the shell, which can be saved to and automatically loaded from persistent storage configured at build-time.

WARNING: Environment variable storage has not been explicitly configured so far and is untested in the context of Libreboot. It may cause data loss or even brick your device by overwriting your disk’s partition table, unexpected parts of the SPI ROM image, or do something else entirely.

Known issues

U-Boot integration in Libreboot is incomplete. Here is a list of known issues that affect all boards:

Branding is U-Boot with their logo (Libreboot only in version number)
Splash screen might be better instead of console messages
Cursor/drawing bugs with video improvements patches
Environment storage is likely dangerously broken
SMBIOS info is missing, Unknown, Unknown Product, etc.
Coreboot tables are ignored, unavailable to the OS
Re-inits display instead of using coreboot framebuffer
Chromebook FMAP layouts should match stock layout for GBB, VPD
Chromebook GBB, VPD are not handled, data may be unavailable to OS
U-Boot “coreboot*” defconfigs needs more work and an ARM64 version
UEFI support is incomplete

Usage

Known issues

See also