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

Prerequirements¶

Make sure you set up the Flexbuild Docker environment properly. Follow the instructions from step 5 of the Build Debian from source code page.

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.