How to compile the device tree with the Developer Package

1. Purpose

This article explains how to update the boot chain (trusted mode) for a "custom" device tree.
In paricular, STM32CubeMX can generate a "custom" device tree.

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

2. Rationale

There are various rationale 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 (or the opposite)

3. Prerequisites

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 are the following:

• Starter package:
  • the flashlayout as well as the images to flash, provided within the IMAGES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz file
• Developer package:
  • the component sources and patches, provided within the SOURCES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz file
  • the SDK toolchain, provided within the SDK-x86_64-st-image-weston-openstlinux-weston-stm32mp1.tar.xz file
• the STM32CubeProgrammer, which is the tool used to flash the images and binaries into the target board.

• 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 tarball MyDeviceTree_fromCubeMX.tar.xz with following file tree:

MyDeviceTree_fromCubeMX
|-- kernel
|   |-- stm32mp157c-mydevicetree-mx.dts
|-- tf-a
|  |-- stm32mp15-mx.h
|  |-- stm32mp157c-mydevicetree-mx.dts
|-- u-boot
|  |-- stm32mp15-mx.h
|  |-- stm32mp157c-mydevicetree-mx-u-boot.dtsi
|  |-- stm32mp157c-mydevicetree-mx.dts

• Make sure the hardware configuration described in PC_prerequisites#Linux PC has been executed (even with a WSL2 setup)

4. Preparing your environnement

As seen in #Pre-requisites, there are numerous inputs so here a proposition to organize your environment.
First create a dedicated WORKDIR under your HOME folder and copy there all the inputs listed in #Pre-requisites:

cd

mkdir WORKDIR

cd WORKDIR

export WORKDIR="$PWD"

tar --strip-components=1 -xf <IMAGES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> -C $WORKDIR/

tar --strip-components=1 -xf <SOURCES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> -C $WORKDIR/

tar --strip-components=1 -xf <SDK-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> -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. Kernel device tree update

Updating the device tree of kernel only needs to replace the 'dtb' file of '/boot' partition.
Indeed 'extlinux.conf' explicitly points on the dtb the kernel should use (something like '/boot/<devicetree>.dtb'). Below the procedure to generate and then copy new DTB in target:

5.1. Kernel : unpack and patch sources

Information

The procedure below is equivalent to chapter 3 of the README_HOWTO.txt file available in $WORKDIR/sources/arm-openstlinux_weston-linux-gnueabi/linux-stm32mp-*

Run following command into a shell:

pushd $WORKDIR

mkdir -p kernel

tar xf sources/arm-openstlinux_weston-linux-gnueabi/linux-stm32mp-4.19-r0/linux-4.19.*.tar.xz -C kernel

mv kernel/linux-* kernel/kernel-sources/

pushd kernel/kernel-sources/

for p in $(ls -1 ../../sources/arm-openstlinux_weston-linux-gnueabi/linux-stm32mp-4.19-r0/*.patch); do patch -p1 < $p; done

popd

popd

5.2. Kernel : copy dts into source code

pushd $WORKDIR

cp -r MyDeviceTree_fromCubeMX/kernel kernel/kernel-sources/arch/arm/boot/dts/

popd

5.3. Kernel : regenerate kernel DTB

Information

The procedure below is equivalent to chapter 5 of the README_HOWTO.txt file available in $WORKDIR/sources/arm-openstlinux_weston-linux-gnueabi/linux-stm32-*

pushd $WORKDIR/kernel/kernel-sources

make O="$PWD/../build" multi_v7_defconfig

for f in `ls -1 ../fragment*.config`; do scripts/kconfig/merge_config.sh -m -r -O $PWD/../build $PWD/../build/.config $f; done

make oldconfig O="$PWD/../build"

make stm32mp157c-mydevicetree-mx LOADADDR=0xC2000040 O="$PWD/../build"

popd

ls -l $WORKDIR/kernel/build/arch/arm/boot/dts/stm32mp157c-mydevicetree-mx.dtb

5.4. Kernel : copy DTB into bootfs

First of all update bootfs with the just new DTB to take it into account on next boot of the target.

Then if needed update extlinux of target according this new dtb filename. This is only needed if the filename of the dtb generated is diferent from the one used by extlinux to boot.

6. U-Boot device tree update

Updating the device tree of u-boot needs to replace the 'dtb' part of the u-boot binary.
By adding new device tree to u-boot source code, the Makefile will regenerate a new u-boot.stm32 containing the new 'dts'

6.1. U-boot : unpack and patch sources

Information

The procedure below is equivalent to chapter 3 of the README_HOWTO.txt file available in $WORKDIR/sources/arm-openstlinux_weston-linux-gnueabi//u-boot-stm32mp-*

pushd $WORKDIR

mkdir -p u-boot

tar xf sources/arm-openstlinux_weston-linux-gnueabi/u-boot-stm32mp-*/v*.tar.gz -C u-boot

mv u-boot/u-boot* u-boot/u-boot-sources/

pushd u-boot/u-boot-sources

for p in $(ls -1 ../../sources/arm-openstlinux_weston-linux-gnueabi/u-boot-stm32mp-*/*.patch); do patch -p1 < $p; done

popd

6.2. U-boot : copy DTS in u-boot source code

pushd $WORKDIR

cp MyDeviceTree_fromCubeMX/u-boot/* u-boot/u-boot-sources/arch/arm/dts/

popd

Since u-boot 2019.04 version the device tree to compile must be explicitly wrote in dts Makefile:

Please, add the device tree to compile into the u-boot/u-boot-sources/arch/arm/dts/Makefile file:

 dtb-y += stm32mp157c-mydevicetree-mx.dtb
 targets += $(dtb-y)

6.3. U-boot : regenerate u-boot.stm32

Information

The procedure below is equivalent to chapter 5.1 of the README_HOWTO.txt file available in $WORKDIR/sources/arm-openstlinux_weston-linux-gnueabi//u-boot-stm32mp-*

pushd $WORKDIR/u-boot/u-boot-sources

make stm32mp15_<config>_defconfig

<config> : could be trusted or basic according the boot type

make DEVICE_TREE=<device tree> all

<device tree> : is the device tree just copied, i.e.: stm32mp157c-mydevicetree-mx

popd

ls -l $WORKDIR/u-boot/u-boot-sources/u-boot.stm32

6.4. U-boot : copy u-boot on target

• Because of 'extlinux' and before flashing the new u-boot.stm32, make sure #extlinux update is done according the 'compatible' value in DTS file.
  

• Then flash the u-boot.stm32 into 'ssbl' partition of the target with STM32CubeProgrammer

7. TF-A device tree update

Updating the device tree of TF-A needs to replace the 'dtb'part of the TF-A binary.
TF-A binary allocates just after the 'mkimage" headers a 'fixed' zone for DTB. DTB is smaller than the reserved zone, padding is done with zero.

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

7.1. TF-A : unpack and patch sources

Information

The procedure below is equivalent to chapter 3 of the README_HOWTO.txt file available in $WORKDIR/sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*

pushd $WORKDIR

mkdir -p tf-a

tar xf sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*/v*.tar.gz -C tf-a

mv tf-a/arm-trusted-firmware-* tf-a/tf-a-sources

pushd tf-a/tf-a-sources

for p in $(ls -1 ../../sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*/*.patch); do patch -p1 < $p; done

popd

popd

7.2. TF-A : copy dts into source code

pushd $WORKDIR

cp -r tf-a/MyDeviceTree_fromCubeMX/tf-a tf-a/tf-a-sources/fdts/

popd

7.3. TF-A : regenerate TF-A.stm32

Information

The procedure below is equivalent to chapter 5 of the README_HOWTO.txt file available in $WORKDIR/st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*

pushd $WORKDIR/tf-a/tf-a-sources

make -f $PWD/../Makefile.sdk TFA_DEVICETREE=<device tree> TF_A_CONFIG=<config> all

<config> : could be trusted or basic according the boot type

<device tree> : is the device tree just copied, i.e.: stm32mp157c-mydevicetree-mx

popd

ls -l $WORKDIR/tf-a/build/<config>/tf-a-<device tree>-<config>.stm32

7.4. TF-A : copy DTB on target/bootfs

Then flash the tf-a-*.stm32 into the 'fsbl1' and 'fsbl2' partitions of the target with STM32CubeProgrammer

Warning

'fsbl1' and 'fsbl2' are two redondant partitions and so, they should have same content

8. Update methods

8.1. bootfs update

• On a target up and running

scp stm32mp157c-mydevicetree-mx.dtb root@<Target_IP>:/boot/

• Into 'bootfs' image directly

This method doesn't need to have a target up and running but only need the "st-image-bootfs-openstlinux-weston-stm32mp1.ext4" file. To modify a 'ext4' file, a loopback mount tool is need which is avaible in any Linux Distribution (even through WSL2):

mkdir -p $WORKING/bootfs

mount -o loop <st-image-bootfs-openstlinux-weston-stm32mp1.ext4> $WORKING/bootfs

##Then copy the new dtb file at the root of $WORKING/bootfs

umount $WORKING/bootfs

sync

dd if=<st-image-bootfs-openstlinux-weston-stm32mp1.ext4> of=/dev/mmblk0p4 conv=fdatasync

Information

The '/dev/mmcblk0p4' is in case of the sdcard is inserted in dedicated drive of the PC, using an USB sdcard reader will probably create /dev/sdb4 entry.

8.2. extlinux update

8.2.1. extlinux : basics

'extlinux' is a collection of scripts/config files describing how u-boot should boots. Updating extlinux consists in updating the extlinux.conf.

• As exemple by using a DK-2 board and booting on sdcard, then the extlinux.conf file is located in "/boot/mmc0_stm32mp157c-dk2_extlinux/".

  If "mmc0_<something>_extlinux" directory is not available, please use "/boot/extlinux/extlinux.conf" file instead.

'extlinux.conf' is the description of a boot menu with one or several entries, 'DEFAULT' selects the one to use by default .
Below an exemple of file:

menu title Select the boot mode
MENU BACKGROUND ../splash.bmp
TIMEOUT 5
DEFAULT stm32mp157c-mydevicetree-mx
LABEL stm32mp157c-dk2-sdcard
        KERNEL /uImage
        FDT /stm32mp157c-dk2.dtb
        APPEND root=/dev/mmcblk0p6 rootwait rw console=ttySTM0,115200
LABEL stm32mp157c-dk2-a7-examples-sdcard
        KERNEL /uImage
        FDT /stm32mp157c-dk2-a7-examples.dtb
        APPEND root=/dev/mmcblk0p6 rootwait rw console=ttySTM0,115200
LABEL stm32mp157c-dk2-m4-examples-sdcard
        KERNEL /uImage
        FDT /stm32mp157c-dk2-m4-examples.dtb
        APPEND root=/dev/mmcblk0p6 rootwait rw console=ttySTM0,115200
LABEL stm32mp157c-mydevicetree-mx
       KERNEL /uImage
       FDT /stm32mp157c-mydevicetree-mx.dtb
       APPEND root=/dev/mmcblk0p6 rootwait rw console=ttySTM0,115200

In example above the highlighted lines may need to be updated/added by this wiki page:

• DEFAULT: This is the default 'LABEL' to boot
• LABEL : The entry 'LABEL' is the value of 'compatible' of the DTS file compiled with u-boot.

  The 'compatible' value is at head of the DTS file and looks like : "st,stm32mp157c-mydevicetree-mx"

• FDT : The path from /boot of the kernel DTB to use

8.2.2. extlinux : updating

Updating 'extlinux' consists into modifying the extlinux.conf. There are 2 ways to proceed:

• On a target up and running

Open a ssh connection to the target or directly with tty terminal, and then use an editor as 'vi' to modify the extlinux.conf file.

Do not forget to synchronize the file system before rebooting the target:

sync

• Into 'bootfs' image directly

This method doesn't need to have a target up and running but only need the "st-image-bootfs-openstlinux-weston-stm32mp1.ext4" file. To modify a 'ext4' file, a loopback mount tool is need which is avaible in any Linux Distribution (even through WSL2):

mkdir -p $WORKING/bootfs

mount -o loop <st-image-bootfs-openstlinux-weston-stm32mp1.ext4> $WORKING/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

Device tree binary (or Blob)

Cortex^®

Linux^® is a registered trademark of Linus Torvalds.

Trusted firmware for Arm^® Cortex^®-A

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

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

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