Since 2014 the Lenovo T420 is replacing my broken Dell XPS M1710. The first thing I did was replacing the HDD with a 256 GB Samsung 840 SSD and installing Arch Linux on it. In the same year I stumbled across coreboot after gathering information related to the Snowden leaks the year before. Until October 2015 there was no support for the T420 in coreboot and the T420 wiki page gave little information about the topic. Months have passed and finally in March 2017 I dealt with the subject again and successfully flashed coreboot 4.5 on my T420, replacing the proprietary BIOS from Lenovo. The wiki page has now much more content and a guide on how to compile and build coreboot, too.
On 15th of October 2017 I built coreboot 4.6 and flashed the new image on my T420 and I am using this version until today. I did the following steps to flash coreboot. Most of the information are copied over from the corebook documentation on the T420.
The pinout of the Rasbperry Pi 3B is the following:
L CS
E |
F +--------------------------------------------------------------------------------------------------------+
T | x x x x x x x x x x x x x x x x x x x x |
| x x x x x x x x x x x x x x x x x x x x |
E +--------------------------------------------^----^----^----^---------------------------------------^----+
D | | | | |
G 3.3V MOSI MISO | GND
E (VCC) CLK
The pinout of the T420 is the following:
Screen __
CS 1 --| |-- 5 MOSI
MISO 2 --| |-- 6 CLK
N/C 3 --| |-- 7 N/C
GND 4 --|__|-- 8 VCC
My chip is a MX25L6406E so I have to provide flashrom with the -c MX25L6406E/MX25L6408E flag to access the chip.
Step 0 - Saving the old Lenovo BIOS
sudo flashrom -c MX25L6406E/MX25L6408E -p linux_spi:dev=/dev/spidev0.0,spispeed=512 -r bios_orig.bin
sudo flashrom -c MX25L6406E/MX25L6408E -p linux_spi:dev=/dev/spidev0.0,spispeed=512 -r bios_orig02.bin
md5sum bios_orig.bin bios_orig02.bin
Step 1 - Install tools and libraries needed for coreboot
sudo zypper in bison curl flashrom gcc-ada
Step 2 - Download coreboot source tree
git clone https://review.coreboot.org/coreboot ~/coreboot
cd coreboot
cd 3dparty/util/ifdtool
make
sudo make install
ifdtool -x ~/bios_orig.bin
mkdir -p ~/coreboot/3rdparty/blobs/mainboard/lenovo/t420
cd ~/coreboot/3rdparty/blobs/mainboard/lenovo/t420
mv ~/flashregion_0_flashdescriptor.bin descriptor.bin
mv ~/flashregion_2_intel_me.bin me.bin
mv ~/flashregion_3_gbe.bin gbe.bin
Step 3 - Build the coreboot toolchain
make crossgcc-i386 CPUS=$(nproc)
Step 4 - Build the payload - coreinfo
make -C payloads/coreinfo olddefconfig
make -C payloads/coreinfo
Step 5 - Configure the build
make menuconfig
# not a complete list
General Setup
Use CMOS for configuration values
Mainboard
Mainboard vendor >>> Select >> Lenovo
Mainboard model >>> Select >>> T420
Chipset
Add Intel descriptor.bin file
Add Intel ME/TXE firmware
Add gigabit ethernet configuration
Devices
Enable PCIe Clock Power Management
Enable PCIe ASPM L1 SubState
Generic Driver
PS/2 keyboard init
Step 6 - build coreboot
make
The BIOS can be found in the folder build.
Step 7 - flash coreboot
# Saving the old bios again to check the cable connection before flashing
sudo flashrom -c MX25L6406E/MX25L6408E -p linux_spi:dev=/dev/spidev0.0,spispeed=512 -r bios01.bin
sudo flashrom -c MX25L6406E/MX25L6408E -p linux_spi:dev=/dev/spidev0.0,spispeed=512 -r bios02.bin
md5sum bios01.bin bios02.bin
sudo flashrom -c MX25L6406E/MX25L6408E -p linux_spi:dev=/dev/spidev0.0,spispeed=512 -w build/coreboot.rom
Update coreboot internally without an external flashing device
When using openSUSE Tumbleweed you have to set iomem=relaxed as kernel parameter according to the flashrom FAQs.
sudo flashrom -c MX25L6406E/MX25L6408E -p internal:laptop=force_I_want_a_brick -w build/coreboot.rom