How to compile the device tree with the Developer Package

1. Purpose

This article explains how to update boot chain (trusted mode) in case of use of a "customised" devicetree.
As exemple, CubeMX is able to generate "customised" devicetree.

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

Information

Even if STMicroelectronics strongly recommends to use a Linux® environment, this article works in WSL2 (Windows Sub-system Linux 2) from Windows 10® (builds 2019 or later)

2. Rationale

The rationale to not use the devicetree provided by OpenSTLinux distribution and prefer a "customised" devicetree is various;

• You made your own board
• You need to swap some IPs from MCU side to MPU side (or reverse)
• For any other reason...

3. Pre-requisites

This article only need to update three software of the complete boot chain (trusted mode); Trusted Firmware A (TF-A), u-boot and the Linux kernel.
Modifying those software need to handle :

• Starter package :

• need flashlayout and images to flash provided from file IMAGES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz

• Developer package :

• Need components sources and patches of the the software to update provided in file SOURCES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz
• Need mkimage for stm32 and dtc utilities which could be provided by file SDK-x86_64-st-image-weston-openstlinux-weston-stm32mp1.tar.xz

• Notice this is optional since 'dtc' and 'mkimage for stm32' could also be provided by your Linux distribution (as Ubuntu, even Ubuntu though WSL)

• Host tools for binary manipulation : tar, patch, ssh/scp, dd and mount loop device

• Those tools are very basic and available in any Linux distribution even on WSL.
• In case of using WSL, mount loop device is only available from WSL2.

• STM32CubeProgrammer: the tool used to flash the images and binaries into target

• Custom devicetree sources:

• For the rest of document the custom devicetree are considered 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

4. Prepare your environnement

As seen in #Pre-requisites, there are numerus inputs so here a proposition to organize your environment.
Better is to create a dedicated WORKDIR somewhere in your HOME. Then copy all inputs quoted in #Pre-requisites in that just created WORKDIR:

cd

mkdir WORKDIR

cd WORKDIR

export WORKDIR="$PWD"

cp <IMAGES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> $WORKDIR/

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

cp <SOURCES-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> $WORKDIR/

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

cp <MyDeviceTree_fromCubeMX.tar.xz> $WORKDIR/

tar xf <MyDeviceTree_fromCubeMX.tar.xz> -C $WORKDIR/

(optional) cp <SDK-x86_64-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> $WORKDIR/

(optional) tar xf <SDK-x86_64-st-image-weston-openstlinux-weston-stm32mp1.tar.xz> -C $WORKDIR/

5. Kernel device tree update

Updating the devicetree 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

Run following command into a shell:

pushd $WORKDIR

mkdir -p kernel

tar xf st-image-weston-openstlinux-weston-stm32mp1/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 ../../st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/linux-stm32mp-4.19-r0/*.patch); do patch -p1 < $p; done

popd

popd

5.2. Kernel : generate DTB

pushd $WORKDIR

cp -r MyDeviceTree_fromCubeMX/kernel kernel/dts

ls kernel/dts/

stm32mp157c-mydevicetree-mx.dts

pushd $WORKDIR

gcc -E -nostdinc -I kernel-sources/include/ -I kernel-sources/arch/arm/boot/dts -I dts -undef -D__DTS__ -x assembler-with-cpp -o stm32mp157c-mydevicetree-mx.dts.tmp dts/stm32mp157c-mydevicetree-mx.dts

dtc -I dts -O dtb -o stm32mp157c-mydevicetree-mx.dtb stm32mp157c-mydevicetree-mx.dts.tmp

Template:Highlight3

popd

popd

5.3. Kernel : copy DTB on target/bootfs

• SCP method (require a up and running target with ssh service):

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

• mount loop device method:

Coming soon

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 devicetree of u-boot needs to replace the 'dtb'part of the u-boot binary.
Indeed u-boot binary is the "concatenation' of the 'dtb' and the 'u-boot' and then packaged with 'mkimage' for stm32.

Below the procedure to generate u-boot with a new DTB and then flash it on "u-boot" partition:

Warning

reminder: only trusted mode is supported

6.1. U-boot : unpack and patch sources

pushd $WORKDIR

mkdir -p u-boot

tar xf st-image-weston-openstlinux-weston-stm32mp1/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 ../../st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/u-boot-stm32mp-*/*.patch); do patch -p1 < $p; done

popd

6.2. U-boot : generate DTB

pushd $WORKDIR/u-boot

cp -r ../MyDeviceTree_fromCubeMX/u-boot dts

ls -1 dts

stm32mp157c-mydevicetree-mx.dts

stm32mp157c-mydevicetree-mx-u-boot.dtsi

stm32mp15-mx.h

## Need to include dtsi u-boot file into dts of u-boot

echo '#include "stm32mp157c-mydevicetree-mx-u-boot.dtsi"' >> dts/stm32mp157c-mydevicetree-mx.dts

gcc -E -nostdinc -I u-boot-sources/include/ -I u-boot-sources/arch/arm/dts -I dts -undef -D__DTS__ -x assembler-with-cpp -o stm32mp157c-mydevicetree-mx.dts.tmp dts/stm32mp157c-mydevicetree-mx.dts

dtc -I dts -O dtb -o u-boot.dtb stm32mp157c-mydevicetree-mx.dts.tmp

popd

6.3. U-boot : regenerate u-boot.stm32

pushd $WORKDIR/u-boot

cat st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/u-boot-stm32mp-*/intermediate-binaries/trusted/u-boot-nodtb.bin u-boot.dtb > u-boot-dtb.bin

#464650

export SYS_TEXT_BASE=0xC0100000

mkimage -T stm32image -a $SYS_TEXT_BASE -e $SYS_TEXT_BASE -d u-boot-dtb.bin 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 the 'extlinux.conf' file, present in '/boot' and used for boot, has an entry ('LABEL') according the 'compatible' value in DTS file.
  

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

• For exemple if you are 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, add an entry in "/boot/extlinux/extlinux.conf" file instead.

  If needed update 'DEFAULT' value also.

 menu title Select the boot mode
 MENU BACKGROUND ../splash.bmp
 TIMEOUT 20
 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

At least 2 methods exist to update the "/boot" filesystem partition, please refer to #update bootfs chapter.

Warning

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

7. TF-A device tree update

Updating the devicetree 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

pushd $WORKDIR

mkdir -p tf-a

tar xf st-image-weston-openstlinux-weston-stm32mp1/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 ../../st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*/*.patch); do patch -p1 < $p; done

popd

popd

7.2. TF-A : generate DTB

pushd $WORKDIR/tf-a

cp -r ../MyDeviceTree_fromCubeMX/tf-a dts

ls -1 dts/

stm32mp157c-mydevicetree-mx.dts

stm32mp15-mx.h

gcc -E -nostdinc -I tf-a-sources/include/ -I tf-a-sources/fdts -I dts -undef -D__DTS__ -x assembler-with-cpp -o stm32mp157c-mydevicetree-mx.dts.tmp dts/stm32mp157c-mydevicetree-mx.dts

dtc -I dts -O dtb -o tf-a.dtb stm32mp157c-mydevicetree-mx.dts.tmp

popd

7.3. TF-A : regenerate TF-A.stm32

## OFFSET of DTB in tf-a.bin (fixed offset) : 0xBB00 (47872 in decimal)

## OFFSET of BL2 in tf-a.bin (fixed offset)  : 0x17B00 (97024 in decimal)

cp st-image-weston-openstlinux-weston-stm32mp1/sources/arm-openstlinux_weston-linux-gnueabi/tf-a-stm32mp-*/intermediate-binaries/trusted/tf-a-Template:LightBlue.bin tf-a.bin

# Delete dtb from tf-a.bin

dd conv=notrunc if=/dev/zero of=tf-a.bin bs=97024 count=1

# copy new dtb into tf-a.bin

dd conv=notrunc if=tf-a.dtb of=tf-a.bin seek=47872 obs=1

## SYS_TEXT_DATA=0x2FFC2500 is the addr of tf-a in memory (could be found in tf-a.map address of '.data' section)

## SYS_TEXT_BL2=0x2FFD4000 is the entry point of tf-a (could be found in tf-a.map address of '.bl2_image' section)

mkimage -T stm32image -a $SYS_TEXT_DATA -e $SYS_TEXT_BL2 -d tf-a.bin tf-a.stm32

7.4. TF-A : copy DTB on target/bootfs

To flash the tf-a.stm32 into target you can use STM32CubeProgrammer or use 'dd' to only flash the TF-A partition:

dd if=tf-a.stm32 of=/dev/mmcblk0p1 conv=fdatasync

dd if=tf-a.stm32 of=/dev/mmcblk0p2 conv=fdatasync

Warning

tf-a.stm32 should be flashed on 2 first partitions of the sdcard

Information

'/dev/mmcblk0pX' is in case of a sdcard inserted in the sdcard drive of the PC, unsing an USB sdcard reader will probably create /dev/sdX entry.

Device tree binary (or Blob)

Linux^® is a registered trademark of Linus Torvalds.

Microcontroller unit (MCUs have internal flash memory and are intended to operate with a minimum amount of external support ICs. They commonly are a self-contained, system-on-chip (SoC) designs.)

Microprocessor unit

Trusted firmware for Arm^® Cortex^®-A

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)

Secure coprocessor

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

Boot loader stage 2