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Customizing U-Boot

Introduction

This guide demonstrates how to patch and rebuild Debian U-Boot images.

To learn how to build the U-Boot images outside of Debian, see: Build U-Boot from source code

Prerequisites

Make sure you set up the FlexBuild Docker environment properly by following FlexBuild Setup and Usage.

Add your patches on top of the Variscite source code

The following steps can be executed outside or inside the container.

Fetch the U-Boot source: 

git clone https://github.com/varigit/uboot-imx -b lf_v2025.04_6.12.49-2.2.0_var01
cd uboot-imx
git clean -fdx
Next, make the desired changes to the U-Boot source code. Example: 
vim drivers/net/fsl_enetc.c
vim drivers/net/fsl_enetc.h
After changing the source code, commit the changes locally and generate a patch file: 
git add .
git commit -e
git format-patch -1
Once the patch is created, copy it to the U-Boot patch folder, which is inside the Flexbuild directory: 
mkdir -p [...]/flexbuild/patch/uboot/
cp 0001-my-changes.patch [...]/flexbuild/patch/uboot/

Build U-Boot individually

Do not run any 'git am' or 'git apply' command. That will be done inside the U-Boot Makefile. Now, if you're not inside the container, get in with the following commands: 

cd [...]/flexbuild           # (Outside Docker environment)
. setup.env                  # (Outside Docker environment)
bld docker                   # (Outside Docker environment)
Once you've entered the Docker environment, run: 
bld -f sdk-var.yml -m imx95-var-dart uboot           # (Inside Docker environment)

Rebuild U-Boot

Once you've built U-Boot, a clean step is needed if a rebuild is required: 

bld clean-bsp                                           # (Inside Docker environment)
Then, just build U-Boot normally with: 
bld -f sdk-var.yml -m imx95-var-dart uboot           # (Inside Docker environment)

Supported hardware variants

The DART-MX95 is available with different RAM size configurations. Currently, a separate image must be compiled for each RAM size.

This can be configured via the OEI_DDR_CONFIG value in the board configuration file: flexbuild/configs/board/imx95-var-dart.conf

Depending on the RAM size, set OEI_DDR_CONFIG to the corresponding value:

  • DART-MX95 2GB: lpddr5_2gb_6400mbps_train_timing
  • DART-MX95 4GB: lpddr5_4gb_6400mbps_train_timing
  • DART-MX95 8GB: lpddr5_8gb_6400mbps_train_timing
  • DART-MX95 16GB: lpddr5_16gb_6400mbps_train_timing

The default configuration is lpddr5_8gb_6400mbps_train_timing.