T420-coreboot

I have followed these guides except that I have used an FT232H instead of a Raspberry Pi for reading and writing the BIOS chip MX25L6406E

• Lenovo T420 Coreboot W/Raspberry Pi
• t420-coreboot-guide

Status: since 2026-07-18 the machine runs Libreboot 26.01rev1 — see the Libreboot update section. config, vgabios.bin and release 20240802 belong to the original 2024 custom coreboot build and are kept for history/rollback.

FT232H

Pinout

FTDI_FT2232H

Name	Color	Test clip pin#	FT232H pin#
/CS	Brown	1	AD3
MISO	Yellow	2	AD2
GND	Black	4	GND
MOSI	Orange	5	AD1
SCLK	Green	6	AD0
VCC	Red	8	+3.3V

Read out the BIOS

flashrom -p ft2232_spi:type=232H -c MX25L6406E/MX25L6408E -r factory1.rom

Write back the compiled BIOS

flashrom -p ft2232_spi:type=232H -c MX25L6406E/MX25L6408E -w coreboot.rom

LIBREBOOT (historical — first attempt notes from 2024)

I looked at the guide below for inspiration; one can't follow it exactly any more as the libreboot project has refactored (especially the vendor files) since it was made. I have used a Debian Bookworm container on top of Proxmox -> 8 GB of RAM and a 15 GB drive (8 GB is too small)

• Installing libreboot on a ThinkPad T420

Download and build the development environment

git clone https://codeberg.org/libreboot/lbmk

Libreboot update (done 2026-07-18, release 26.01rev1)

Running Libreboot t420_8mb, seagrub_..._corebootfb_svenska.rom (SeaBIOS + GRUB, libgfxinit, neutered ME). Built in a Proxmox CT with Debian Trixie; flashed internally on the T420 (kernel arg iomem=relaxed), no clip needed.

# 1. On the T420: backup current flash (read twice, sha256sum must match, keep off-laptop)
sudo flashrom -p internal -c MX25L6406E/MX25L6408E -r backup-a.rom

# 2. In the Proxmox CT (only dependencies as root, lbmk refuses sudo otherwise)
git clone https://codeberg.org/libreboot/lbmk && cd lbmk
git fetch --tags && git checkout <RELEASE>      # e.g. 26.01rev1
sudo ./mk dependencies debian

# 3. Get + verify ROMs (mirror: mirrors.mit.edu/libreboot/stable/<RELEASE>/roms/)
wget <mirror>/libreboot-<RELEASE>_t420_8mb.tar.xz{,.sha512,.sig}
sha512sum -c *.sha512 && gpg --verify *.sig     # key: libreboot.org/lbkey.asc

# 4. Inject neutered ME + onboard NIC MAC  (stale "cannot create lock"? -> rm -f lock)
./mk inject libreboot-<RELEASE>_t420_8mb.tar.xz setmac 00:21:cc:61:b8:5c

# 5. Extract tarball, take bin/t420_8mb/seagrub_..._corebootfb_svenska.rom
#    (ignore cache/DO_NOT_FLASH/)

# 6. On the T420, AC plugged in, wait for VERIFIED — on error reflash backup, do NOT reboot
sudo flashrom -p internal:boardmismatch=force -c MX25L6406E/MX25L6408E -w <rom>

First boot is slow / may reset once (memory training). Bricked: FT232H + clip, write backup-a.rom.

Update flash after it has been flashed the first time (historical — superseded by the Libreboot update section above)

• How do I "edit grub to add iomem=relaxed"?

sudo flashrom -p internal:boardmismatch=force -c MX25L6406E/MX25L6408E -w coreboot.rom

Tested hardware

• Updated CPU to Intel i7-3632QM — with coreboot one can go to Ivy Bridge
• AX210 Mini PCIe WLAN 6E card
• BE200 Mini PCIe WLAN 7 card
• mSATA SanDisk U100 in the Mini PCIe slot next to the RAM in the bottom