How to compile the device tree with the Developer Package

Applicable for STM32MP15x lines

1 Purpose[edit]

This article explains how to update the boot chain (OP-TEE with FIP) for a "custom" device tree.
This article concentrates in particular on generating a "custom" device tree based on theSTM32CubeMX.

This article describes how to update the device tree compiled (DTB) part of the boot binaries.

2 Rationale[edit]

There are various reasons for using a custom device tree, such as:

  • the description of a new and private board
  • the swapping of some internal peripherals from Cortex®-M side to Cortex-A side (and vice versa)

3 Prerequisites[edit]

Info white.png Information
Even if STMicroelectronics strongly recommends to use a Linux® environment, the steps described in this article can be executed in a WSL2 (Windows Sub-system Linux 2) environment.

Compiling a new device tree means updating three software components belonging to the complete boot chain (trusted mode), Trusted Firmware A (TF-A), U-Boot, and Linux kernel.


The material required to update the above software components is the following:


  • Custom device tree sources:
    • In the rest of this document, we assume that the custom device tree is generated by STM32CubeMX and stored in a MyDeviceTree_fromCubeMX.tar.xz tarball with following file tree:
MyDeviceTree_fromCubeMX
|-- kernel
|   |-- stm32mp157f-mydevicetree-mx.dts
|-- tf-a
|  |-- stm32mp157f-mydevicetree-mx.dts
|  |-- stm32mp157f-mydevicetree-mx-fw-config.dts
|  |-- stm32mp15-mx.dtsi
|-- u-boot
|  |-- stm32mp157f-mydevicetree-mx.dts
|  |-- stm32mp157f-mydevicetree-mx-u-boot.dtsi
|  |-- stm32mp15-mx.dtsi


4 Preparing your environment[edit]

It is recommended to organize the numerous inputs described in #Prerequisites in your environment.
First create a dedicated WORKDIR under your HOME folder and copy there all the inputs listed in #Prerequisites:

cd $HOME
mkdir WORKDIR
cd WORKDIR
export WORKDIR="$PWD"
tar --strip-components=1 -xf en.FLASH-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.11.23.tar.gz -C $WORKDIR/
tar --strip-components=1 -xf en.SOURCES-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.11.23.tar.gz -C $WORKDIR/
tar --strip-components=1 -xf en.SDK-x86_64-stm32mp1-openstlinux-5.15-yocto-kirkstone-mp1-v22.11.23.tar.gz -C $WORKDIR/
tar xf <MyDeviceTree_fromCubeMX.tar.xz> -C $WORKDIR/

Then proceed with the SDK installation.


The commands described in the rest of the document must be run in an SDK environment context: (Starting_up_the_SDK).

5 Updating the kernel device tree[edit]

Since 'extlinux.conf' explicitly points to the DTB, just update the kernel device tree by replacing the DTB file of the '/boot' partition. The path used must be something like '/boot/<devicetree>.dtb'.

The following chapters describe the procedure to generate and copy the new DTB into the target.

5.1 Kernel : unpack and patch sources[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/linux-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of kernel

.

Run the following command into a shell:

pushd $WORKDIR
mkdir -p kernel
tar xf sources/arm-ostl-linux-gnueabi/linux-stm32mp-*/linux-*.tar.xz -C kernel
mv kernel/linux-* kernel/kernel-sources/
pushd kernel/kernel-sources/
for p in $(ls -1 ../../sources/arm-ostl-linux-gnueabi/linux-stm32mp-*/*.patch); do patch -p1 < $p; done
popd
popd

5.2 Kernel : copy the DTS into the source code[edit]

pushd $WORKDIR
cp -r MyDeviceTree_fromCubeMX/kernel/* kernel/kernel-sources/arch/arm/boot/dts/
popd

5.3 Kernel : regenerate the kernel DTB[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/linux-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of kernel

.

pushd $WORKDIR/kernel/kernel-sources
make ARCH=arm O="$PWD/../build" multi_v7_defconfig fragment*.config
for f in `ls -1 ../../sources/arm-ostl-linux-gnueabi/linux-stm32mp-*/fragment*.config`; do scripts/kconfig/merge_config.sh -m -r -O $PWD/../build $PWD/../build/.config $f; done
yes "" | make ARCH=arm oldconfig O="$PWD/../build"
make stm32mp157f-mydevicetree-mx.dtb LOADADDR=0xC2000040 O="$PWD/../build"
popd
ls -l $WORKDIR/kernel/build/arch/arm/boot/dts/stm32mp157f-mydevicetree-mx.dtb

5.4 Kernel : copy the DTB into bootfs[edit]

First, update all the #Updating bootfs with the new DTB for it to be taken it into account on the next boot of the target.

Then, if needed, edit by #Updating extlinux for the target with this new DTB filename. This is only required if the filename of the generated DTB is different from the one used by extlinux to boot.

6 Updating BOOT firmwares[edit]

The BOOT firmwares are TF-A and U-Boot and must be updated together (CubeMX provides devicetree for TF-A and U-Boot).

6.1 Updating the TF-A device tree[edit]

To update the TF-A device tree, replace the DTB part of the TF-A binary.
The TF-A binary allocates a 'fixed' area for the DTB, just after the 'mkimage" headers. If the DTB is smaller than the reserved area, the remaining memory is padded with zero.

Below the procedure to generate TF-A with a new DTB and then flash it on the target:

6.1.1 TF-A : unpack and patch sources[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/tf-a-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of tf-a

.

pushd $WORKDIR
pushd sources/arm-ostl-linux-gnueabi/tf-a-stm32mp-v[0-9]*
mkdir -p tf-a-sources
tar xf tf-a-stm32mp-v[0-9]*.tar.* --one-top-level=tf-a-sources --strip-components=1
pushd tf-a-sources
for p in `ls -1 ../*.patch`; do patch -p1 < $p; done
popd
popd

6.1.2 TF-A : copy the DTS into the source code[edit]

pushd $WORKDIR
cp -r MyDeviceTree_fromCubeMX/tf-a/* sources/arm-ostl-linux-gnueabi/tf-a-stm32mp-v[0-9]*/tf-a-sources/fdts/
popd

6.1.3 TF-A : regenerate TF-A[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/tf-a-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of tf-a

.

First only the TF-A "intermediates" artifacts are generated, the FIP image will be generated at final step (U-Boot compilation).


pushd $WORKDIR/sources/arm-ostl-linux-gnueabi/tf-a-stm32mp-v[0-9]*/tf-a-sources
export FIP_DEPLOYDIR_ROOT=$PWD/../../FIP_artifacts
make -f ../Makefile.sdk TF_A_DEVICETREE=<devicetree_name> TF_A_CONFIG="optee emmc nand nor sdcard uart usb" DEPLOYDIR=$FIP_DEPLOYDIR_ROOT/arm-trusted-firmware stm32
<devicetree_name> : is the device tree just copied, i.e.: stm32mp157f-mydevicetree-mx
DEPLOYDIR is the path where intermediate binaries of tf-a should be deployed (requiered by fip-tools to generate fip image)
popd

6.2 Updating the OP-TEE device tree[edit]

To update the OP-TEE device tree, replace the DTB part of the OP-TEE binary.
Adding a new device tree to the OP-TEE source code forces the Makefile to regenerate new OP-TEE binaries.
The following chapters describe the procedure to update the OP-TEE device tree.

6.2.1 OP-TEE: unpack and patch sources[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/optee-os-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of OP-TEE

.

pushd $WORKDIR
pushd sources/arm-ostl-linux-gnueabi/optee-os-stm32mp-[0-9]*
tar xf optee-os-stm32mp-[0-9]*.tar.* --one-top-level=optee-os-sources --strip-components=1
pushd optee-os-sources
tar xfz ../fonts.tar.gz
for p in `ls -1 ../*.patch`; do patch -p1 < $p; done
popd
popd

6.2.2 OP-TEE: copy the DTS in the source code[edit]

pushd $WORKDIR
cp MyDeviceTree_fromCubeMX/optee/* sources/arm-ostl-linux-gnueabi/optee-os-stm32mp-*/optee-os-sources/core/arch/arm/dts/
popd

6.2.3 OP-TEE: regenerate fip image within new OP-TEE[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of OP-TEE

.

pushd $WORKDIR/sources/arm-ostl-linux-gnueabi/optee-os-stm32mp-[0-9]*/optee-os-sources
make -f ../Makefile.sdk CFG_EMBED_DTB_SOURCE_FILE=<device tree> OPTEE_DRAMSIZE=<RAM size> DEPLOYDIR=~/views/temp/CubeIde/WORKDIR/sources/arm-ostl-linux-gnueabi/FIP_artifacts/optee optee
<device tree> : is the device tree just copied, i.e.: stm32mp157f-mydevicetree-mx
<RAM size>  : is the RAM size of the board selected by the device treee, i.e.: 0x20000000
popd

6.3 Updating the U-Boot device tree[edit]

To update the U-Boot device tree, replace the U-Boot DTB in FIP image.

6.3.1 U-Boot : unpack and patch sources[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of U-Boot

.

pushd $WORKDIR
pushd sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-v[0-9]*
tar xf u-boot-stm32mp-v[0-9]*.tar.* --one-top-level=u-boot-sources --strip-components=1
pushd u-boot-sources
for p in `ls -1 ../*.patch`; do patch -p1 < $p; done
popd
popd

6.3.2 U-Boot : copy the DTS in the U-Boot source code[edit]

pushd $WORKDIR
cp MyDeviceTree_fromCubeMX/u-boot/* sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-v[0-9]*/u-boot-sources/arch/arm/dts/
popd

6.3.3 U-Boot : regenerate fip image within new U-Boot binary[edit]

Info white.png Information
The procedure below is an extract of the README.HOW_TO.txt file which is available in $WORKDIR/sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-*. Note: the "README.HOW_TO.txt" file contains some useful grep "$> commands that are needed to build the artifact of U-Boot

.

pushd $WORKDIR/sources/arm-ostl-linux-gnueabi/u-boot-stm32mp-v[0-9]*/u-boot-sources
make -f ../Makefile.sdk UBOOT_CONFIG=trusted UBOOT_DEFCONFIG=<stm32mpu device>_defconfig UBOOT_BINARY=u-boot.dtb FIP_CONFIG="optee" DEVICETREE=<device tree> all
<stm32mpu device> : is the targetted stm32mpu device, stm32mp13 or stm32mp15
<device tree> : is the device tree just copied, i.e.: stm32mp157f-mydevicetree-mx
popd

6.3.4 U-Boot : copy U-Boot binary into the target[edit]

  • Because of 'extlinux' and before flashing the new fip image, make sure #Updating extlinux is compliant with the 'compatible' value in the DTS file.
  • Then, using STM32CubeProgrammer, flash the tf-a-xxxx.stm32 file (generated at tf-a step) into the 'fsbl1' and 'fsbl2' partition of the target and the 'fip-a' partition with fip-stm32mpxxxx.bin file (generated just above).

7 Update methods[edit]

7.1 Updating extlinux[edit]

7.1.1 extlinux basics[edit]

extlinux describes how U-Boot boots. Updating extlinux consists in updating the extlinux.conf:

  • In case of an DK-2 board booting from the sdcard. A stm32mp157f-dk2_extlinux.conf file is located in /boot/mmc0_extlinux/,
  • otherwise if there is no specific extlinux.conf for your board, then the extlinux.conf is taking into account.

extlinux.conf is the description of a boot menu with one or several entries; 'DEFAULT' selects the default entry.
Below an example of extlinux.conf: 

menu title Select the boot mode
MENU BACKGROUND ../splash.bmp
TIMEOUT 5
DEFAULT stm32mp157f-mydevicetree-mx
LABEL stm32mp157f-dk2-sdcard
        KERNEL /uImage
        FDTDIR /
        APPEND root=PARTUUID=e91c4e10-16e6-4c0e-bd0e-77becf4a3582 rootwait rw console=ttySTM0,115200
LABEL stm32mp157f-dk2-a7-examples-sdcard
        KERNEL /uImage
        FDT /stm32mp157f-dk2-a7-examples.dtb
        APPEND root=PARTUUID=e91c4e10-16e6-4c0e-bd0e-77becf4a3582 rootwait rw console=ttySTM0,115200
LABEL stm32mp157f-dk2-m4-examples-sdcard
        KERNEL /uImage
        FDT /stm32mp157f-dk2-m4-examples.dtb
        APPEND root=PARTUUID=e91c4e10-16e6-4c0e-bd0e-77becf4a3582 rootwait rw console=ttySTM0,115200
LABEL stm32mp157f-mydevicetree-mx
       KERNEL /uImage
       FDT /stm32mp157f-mydevicetree-mx.dtb
       APPEND root=PARTUUID=e91c4e10-16e6-4c0e-bd0e-77becf4a3582 rootwait rw console=ttySTM0,115200

Please update/add the highlighted lines according to what have been compiled in chapter 5, 6 and/or 7:

  • DEFAULT: This is the default 'LABEL' to boot
  • LABEL : The entry 'LABEL' is the value of 'compatible' of the DTS file used by U-Boot.
    The 'compatible' value is at head of the DTS file and looks like : "st,stm32mp157f-mydevicetree-mx"
  • FDT : The path from /boot of the kernel DTB to use

7.2 Updating bootfs[edit]

There are two methods to update bootfs:

  • On an up and running target
scp stm32mp157f-mydevicetree-mx.dtb root@<Target_IP>:/boot/
  • Directly into 'bootfs' image

You do not need to have a target up and running. Only the "st-image-bootfs-openstlinux-weston-stm32mp1.ext4" file is required. To modify an 'ext4' file, a loopback mount, available within any Linux Distribution (even through WSL2), is required:

mkdir -p $WORKDIR/bootfs
mount -o loop <st-image-bootfs-openstlinux-weston-stm32mp1.ext4> $WORKDIR/bootfs
##Then copy the new dtb file at the root of $WORKDIR/bootfs
umount $WORKDIR/bootfs
sync

Then use STM32CubeProgrammer to update the bootfs partition.

7.2.1 Updating extlinux[edit]

Updating 'extlinux' consists in modifying the extlinux.conf. There are two ways to proceed:

  • On an up and running target

Open an ssh connection to the target or use a direct connection with a tty terminal. Then use an vi editor to modify the extlinux.conf file.

Do not forget to synchronize the file system before rebooting the target:
sync
  • Into 'bootfs' image directly

You do not need to have a target up and running. Only the "st-image-bootfs-openstlinux-weston-stm32mp1.ext4" file is required. To modify an 'ext4' file, a loopback mount tool, available in any Linux Distribution (even through WSL2), is needed:

mkdir -p $WORKDIR/bootfs
sudo mount -o loop <st-image-bootfs-openstlinux-weston-stm32mp1.ext4> $WORKDIR/bootfs
##Then edit the extlinux.conf file (for WSL2 use a 'Linux' type editor; vi, ...)
##Once extlinux.conf up-to-date, umount loopback and flash the bootfs into sdcard with STM32CubeProgrammer



Open portable trusted execution environment

Firmware image package is a packaging format used by TF-A

Device tree binary (or Blob)

Cortex®

Linux® is a registered trademark of Linus Torvalds.

Trusted firmware for Arm® Cortex®-A

Das U-Boot -- the universal boot loader (see U-Boot)

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)

Device tree source (in software context) or digital temperature sensor (in peripheral context)

Random access memory (Early computer memories generally hadserial access. Memories where any given address can be accessed when desired were then called "random access" to distinguish them from the memories where contents can only be accessed in a fixed order. The term is used today for volatile random-acces ssemiconductor memories.)

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