# Internal details

## Minimal configurations

In this section, we describe step by step the minimal Buildroot
configuration
[st_stm32mp157c_dk2_defconfig](/configs/st_stm32mp157c_dk2_defconfig)
which targets the STM32MP157C Discovery Kit 2 platform. The other
Buildroot configurations for the other platforms are very similar.

```
BR2_arm=y
BR2_cortex_a7=y
```

Obviously, this tells Buildroot to build a system for the ARM
architecture, and more precisely for a Cortex-A7 based processor. This
will ensure the cross-compilation toolchain targets the correct CPU
architecture and specific CPU core.

```
BR2_TOOLCHAIN_EXTERNAL=y
```

We decide to use external toolchain. This choice has been made to
reduce the build time of the overall system, and use a well-known
toolchain provided by ARM.

```
BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/patches/"
```

We need to apply one patch to the Linux kernel, which is located in
`board/stmicroelectronics/stm32mp1/patches/`. This configuration
option tells Buildroot where to find the patches to apply.

```
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
```

This option enables *mdev* (a minimal re-implementation of *udev*
which is part of BusyBox) which takes care of automatically loading
kernel modules, adjusting `/dev` nodes permissions, and more.

```
BR2_ROOTFS_OVERLAY="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/overlay/"
```

This tells Buildroot to copy the contents of
[board/stmicroelectronics/stm32mp1/overlay](/board/stmicroelectronics/stm32mp1/overlay)
into the root filesystem. The important file that this copies to the
root filesystem is `/boot/extlinux.conf`, which tells the U-Boot
bootloader how to boot the Linux system (which Linux kernel image to
load, which Device Tree to use, which kernel arguments to pass). It
also adds the Wifi firmware and the sound configuration files but
these are only used in the *demo* configurations, not the minimal
ones.

```
BR2_ROOTFS_POST_BUILD_SCRIPT="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-build.sh"
```

This tells Buildroot to run
[board/stmicroelectronics/stm32mp1/post-build.sh](/board/stmicroelectronics/stm32mp1/post-build.sh)
at the end of the rootfs generation. This script update the
extlinux.conf of the overlay to use the correct Device Tree file at
boot.

```
BR2_ROOTFS_POST_IMAGE_SCRIPT="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-image.sh"
```

This tells Buildroot to run
[board/stmicroelectronics/stm32mp1/post-image.sh](/board/stmicroelectronics/stm32mp1/post-image.sh)
at the end of the build. This script produces the final `sdcard.img`
file using a tool called `genimage` and deploys the `flash.tsv` file to
flash the board with STM32 Cube Programmer.

```
BR2_ROOTFS_POST_SCRIPT_ARGS="genimage.cfg"
```

This is an argument passed to the scripts. It is used by `post-image.sh`
to know which genimage config to use.

```
BR2_LINUX_KERNEL=y
BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="$(call github,STMicroelectronics,linux)v6.1-stm32mp-r1.1.tar.gz"
BR2_LINUX_KERNEL_DEFCONFIG="multi_v7"
BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="$(LINUX_DIR)/arch/arm/configs/fragment-01-multiv7_cleanup.config $(LINUX_DIR)/arch/arm/configs/fragment-02-multiv7_addons.config $(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/linux-disable-etnaviv.config $(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/linux-rauc.config"
BR2_LINUX_KERNEL_DTS_SUPPORT=y
BR2_LINUX_KERNEL_INTREE_DTS_NAME="stm32mp157c-dk2"
BR2_LINUX_KERNEL_INSTALL_TARGET=y
BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
```

This set of options tells Buildroot to build a Linux kernel, with the
source code fetched using Git from the repository at
[https://github.com/STMicroelectronics/linux](https://github.com/STMicroelectronics/linux). The
Git tag `v6.1-stm32mp-r1` will be used as the kernel version. The
kernel will be configured using the configuration file
[multi_v7_defconfig](https://github.com/STMicroelectronics/linux/arch/arm/configs/multi_v7_defconfig)
extended with three configuration fragments:

1. [fragment-01-multiv7_cleanup.config](https://github.com/STMicroelectronics/linux/arch/arm/configs/fragment-01-multiv7_cleanup.config),
which comes from the ST kernel tree, and that disables a number of
kernel drivers/features that are not needed on STM32MP1

2. [fragment-02-multiv7_addons.config](https://github.com/STMicroelectronics/linux/arch/arm/configs/fragment-02-multiv7_addons.config),
which comes from the ST kernel tree, and which enables a few
additional kernel drivers/features taht are relevant on STM32MP1

3. [linux-disable-etnaviv.config](/board/stmicroelectronics/stm32mp1/linux-disable-etnaviv.config),
which comes from this `BR2_EXTERNAL`, and is in charge of disabling
the Etnaviv GPU kernel driver, as we use the proprietary GPU driver
provided by ST instead.

4. [linux-enable-rauc.config](/board/stmicroelectronics/stm32mp1/linux-enable-rauc.config),
which comes from this `BR2_EXTERNAL`, and is in charge of enabling
the requisite kernel drivers to use RAUC OTA tool.

The option `BR2_LINUX_KERNEL_INTREE_DTS_NAME` indicates that the
`stm32mp157c-dk2.dtb` Device Tree file will be produced and should be
used. Finally `BR2_LINUX_KERNEL_INSTALL_TARGET=y` tells that the
kernel image should be installed to the target root filesystem, in
`/boot`.

```
BR2_TARGET_ROOTFS_EXT2=y
BR2_TARGET_ROOTFS_EXT2_4=y
BR2_TARGET_ROOTFS_EXT2_SIZE="120M"
# BR2_TARGET_ROOTFS_TAR is not set
```

This set of options tell Buildroot to generate an *ext4* filesystem
image for the root filesystem, and to not build the default filesystem
image, which is a tarball (`.tar`).

```
BR2_TARGET_ARM_TRUSTED_FIRMWARE=y
BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_TARBALL=y
BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_TARBALL_LOCATION="$(call github,STMicroelectronics,arm-trusted-firmware)v2.8-stm32mp-r1.1.tar.gz"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_PLATFORM="stm32mp1"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_FIP=y
BR2_TARGET_ARM_TRUSTED_FIRMWARE_BL32_OPTEE=y
BR2_TARGET_ARM_TRUSTED_FIRMWARE_UBOOT_AS_BL33=y
BR2_TARGET_ARM_TRUSTED_FIRMWARE_UBOOT_BL33_IMAGE="u-boot-nodtb.bin"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES="STM32MP_SDMMC=1 AARCH32_SP=optee DTB_FILE_NAME=stm32mp157c-dk2.dtb BL33_CFG=$(BINARIES_DIR)/u-boot.dtb STM32MP_USB_PROGRAMMER=1 STM32MP1_OPTEE_IN_SYSRAM"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_IMAGES="*.stm32 fip.bin"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_NEEDS_DTC=y
```

These options tell Buildroot how to build TF-A, the Trusted
Firmware. It is retrieved from the Git repository at
[https://github.com/STMicroelectronics/arm-trusted-firmware](https://github.com/STMicroelectronics/arm-trusted-firmware),
using version `v2.8-stm32mp-r1`. TF-A is configured for the `stm32mp1`
platform with OP-TEE as BL32, and we use the mechanism of
[FIP](https://trustedfirmware-a.readthedocs.io/en/latest/getting_started/tools-build.html)
images. The Device Tree file being used in TF-A comes from the TF-A
source code, and is named `stm32mp157c-dk2.dtb`.

```
BR2_PACKAGE_OPTEE_CLIENT=y
...
BR2_TARGET_OPTEE_OS=y
BR2_TARGET_OPTEE_OS_CUSTOM_TARBALL=y
BR2_TARGET_OPTEE_OS_CUSTOM_TARBALL_LOCATION="$(call github,STMicroelectronics,optee_os)3.19.0-stm32mp-r1.1.tar.gz"
BR2_TARGET_OPTEE_OS_PLATFORM="stm32mp1"
BR2_TARGET_OPTEE_OS_PLATFORM_FLAVOR="157C_DK2"
BR2_TARGET_OPTEE_OS_ADDITIONAL_VARIABLES="CFG_STM32MP1_OPTEE_IN_SYSRAM=y"
```

These options configure the build of OP-TEE as a trusted execution
environment, as well as the user-space OP-TEE client programs.
It is fetched from the Git repository
[https://github.com/STMicroelectronics/optee_os](https://github.com/STMicroelectronics/optee_os),
in version `3.19.0-stm32mp-r1`. The platform is `stm32mp1` and its flavor
is `157C_DK2`

```
BR2_TARGET_UBOOT=y
BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
BR2_TARGET_UBOOT_CUSTOM_TARBALL=y
BR2_TARGET_UBOOT_CUSTOM_TARBALL_LOCATION="$(call github,STMicroelectronics,u-boot)v2022.10-stm32mp-r1.1.tar.gz"
BR2_TARGET_UBOOT_BOARD_DEFCONFIG="stm32mp15"
# BR2_TARGET_UBOOT_FORMAT_BIN is not set
BR2_TARGET_UBOOT_FORMAT_CUSTOM=y
BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="u-boot-nodtb.bin u-boot.dtb"
BR2_TARGET_UBOOT_CUSTOM_MAKEOPTS="DEVICE_TREE=stm32mp157c-dk2"
```

These options tell Buildroot how to build U-Boot: it is fetched from
the Git repository at
[https://github.com/STMicroelectronics/u-boot](https://github.com/STMicroelectronics/u-boot),
in version `v2022.10-stm32mp-r1`. The configuration used is
`stm32mp15`, and we install both the `u-boot-nodtb.bin` and
`u-boot.dtb` images as both are used for the TF-A build. The Device
Tree file used comes from the U-Boot source code, and is named
`stm32mp157c-dk2`.

```
BR2_PACKAGE_HOST_BMAP_TOOLS=y
```

This option tells Buildroot to build the `bmap` utility for the host. This
is used to produce block map files alongside the image.

```
BR2_PACKAGE_HOST_GENIMAGE=y
```

This last option tells Buildroot to build the `genimage` utility for
the host, as it is used to produce the SD card image.

What is not visible in this configuration are all the defaults that
Buildroot has: it will by default integrate Busybox in the root
filesystem image, and use a number of sane defaults to build a basic
embedded Linux system.

## Demo configurations

In this section, we describe the demo configuration
[st_stm32mp157c_dk2_demo_defconfig](/configs/st_stm32mp157c_dk2_demo_defconfig)
for the STM32MP157C Discovery Kit 2. Here as well, all other *demo*
configurations for the other platforms are very similar.

```
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_ARMV7_EABIHF_GLIBC_STABLE=y
```
We use Bootlin toolchain instead of ARM toolchain because we need glibc
2.34 for the latest gcnano-binary libraries.

```
BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/patches/ $(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/patches-demo/"
```

Add patches-demo folder in addition to global patch directory.

```
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
```

This option enables *eudev* instead of *mdev* selected by the basic
configuration. It manages devices node and handles all user space actions
when adding or removing devices.

```
BR2_ROOTFS_POST_BUILD_SCRIPT="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-build.sh $(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-build-demo.sh"
BR2_ROOTFS_POST_IMAGE_SCRIPT="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-image.sh $(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/post-image-demo.sh"
BR2_ROOTFS_POST_SCRIPT_ARGS="genimage-demo.cfg"
```

Add demo post-build and post-image scripts in addition of basique scripts
alongside with genimage-demo args to tell which partition configuratoin
to use.

```
BR2_TARGET_GENERIC_ROOT_PASSWD="root"
```

This option sets the root password to `root`. The root password has to
be set to a non-empty value to connect to the board through SSH.

```
BR2_LINUX_KERNEL_INTREE_DTS_NAME="stm32mp157c-dk2-mx"
BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/linux-dts/*"
BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT=y
```

The demo configurations use a Linux kernel Device Tree file produced
by STM32 Cube MX. These two options tell Buildroot where to find these
Device Tree files, and which one to use. The last option enables the
`-@` Device Tree compiler build option, which produces Device Tree
files with slightly more information, making it possible for the
U-Boot bootloader to automatically tweak the Device Tree files passed
to the Linux kernel when booting.

```
BR2_PACKAGE_OPTEE_EXAMPLES=y
BR2_PACKAGE_OPTEE_TEST=y
```

These options enable OP-TEE tests and examples.

```
BR2_PACKAGE_ALSA_UTILS=y
BR2_PACKAGE_ALSA_UTILS_AMIXER=y
BR2_PACKAGE_ALSA_UTILS_APLAY=y
BR2_PACKAGE_ALSA_UTILS_SPEAKER_TEST=y
```

These options enable alsa-utils and examples.

```
BR2_PACKAGE_DEJAVU=y
BR2_PACKAGE_QT5=y
BR2_PACKAGE_QT5BASE_EXAMPLES=y
BR2_PACKAGE_QT5BASE_GUI=y
BR2_PACKAGE_QT5BASE_OPENGL_LIB=y
BR2_PACKAGE_QT5BASE_EGLFS=y
BR2_PACKAGE_QT5BASE_FONTCONFIG=y
```

These options enable a font (*DejaVu*) and the QT5 graphical toolkit.

```
BR2_PACKAGE_DROPBEAR=y
```

This option enables the dropbear SSH server.

```
BR2_PACKAGE_LINUX_FIRMWARE=y
BR2_PACKAGE_LINUX_FIRMWARE_BRCM_BCM43XXX=y
BR2_PACKAGE_MURATA_CYW_FW=y
BR2_PACKAGE_MURATA_CYW_FW_CYW43430=y
```

These options enable the installation of the firmware file needed for
the WiFi and Bluetooth chips.

```
BR2_PACKAGE_GCNANO_BINARIES=y
```

This option enables the installation of the closed-source user-space
library that provide OpenGL support.

```
BR2_PACKAGE_LIBUBOOTENV=y
```

This option enable tools to read and write the U-boot environment from
Linux. It is requisite to have the [OTA](/docs/ota.md) working properly.

```
BR2_PACKAGE_LIBDRM_INSTALL_TESTS=y
```

This option, which implies `BR2_PACKAGE_LIBDRM=y` installs the
`modetest` utility that we use for [display testing](/docs/display.md).

```
BR2_PACKAGE_BLUEZ_TOOLS=y
BR2_PACKAGE_BLUEZ5_UTILS=y
BR2_PACKAGE_BLUEZ5_UTILS_CLIENT=y
```

These options install the user-space utilities to manage and configure
Bluetooth.

```
BR2_PACKAGE_IW=y
BR2_PACKAGE_WIRELESS_REGDB=y
BR2_PACKAGE_WPA_SUPPLICANT=y
BR2_PACKAGE_WPA_SUPPLICANT_AP_SUPPORT=y
BR2_PACKAGE_WPA_SUPPLICANT_WIFI_DISPLAY=y
BR2_PACKAGE_WPA_SUPPLICANT_AUTOSCAN=y
BR2_PACKAGE_WPA_SUPPLICANT_EAP=y
BR2_PACKAGE_WPA_SUPPLICANT_CLI=y
BR2_PACKAGE_WPA_SUPPLICANT_PASSPHRASE=y
```

These options install the user-space utilities to manage and configure
WiFi, as well as the wireless regulatory database.

```
BR2_PACKAGE_RAUC=y
BR2_PACKAGE_RAUC_DBUS=y
BR2_PACKAGE_RAUC_GPT=y
BR2_PACKAGE_RAUC_NETWORK=y
BR2_PACKAGE_RAUC_STREAMING=y
BR2_PACKAGE_RAUC_JSON=y
```

These options install the rauc tool for [OTA](/docs/ota.md).

```
BR2_TARGET_ROOTFS_SQUASHFS=y
```

This options tell Buildroot to generate a *squashfs* read-only filesystem
image for the root filesystem;

```
BR2_TARGET_ARM_TRUSTED_FIRMWARE_BL32_OPTEE=y
..
BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/tfa-dts/*"
BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES="STM32MP_SDMMC=1 AARCH32_SP=optee DTB_FILE_NAME=stm32mp157c-dk2-mx.dtb STM32MP_USB_PROGRAMMER=1 STM32MP1_OPTEE_IN_SYSRAM=1"
```

These options customize the build of TF-A to load OP-TEE as a trusted
execution environment, and to use a Device Tree file produced by STM32
Cube MX, called `stm32mp157c-dk2-mx.dtb`.

```
BR2_TARGET_OPTEE_OS_CUSTOM_DTS_PATH="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/optee-dts/*"
BR2_TARGET_OPTEE_OS_ADDITIONAL_VARIABLES="CFG_EMBED_DTB_SOURCE_FILE=stm32mp157c-dk2-mx.dts CFG_STM32MP15=y CFG_STM32MP1_OPTEE_IN_SYSRAM=y"
```

These options customize the build of OPTEE-OS to use a Device Tree file
produced by STM32 Cube MX, called `stm32mp157c-dk2-mx`. The option
`CFG_EMBED_DTB_SOURCE_FILE=stm32mp157c-dk2-mx.dts CFG_STM32MP15=y` has been
added to OPTEE-OS make options, to build the external devicetree.

```
BR2_TARGET_UBOOT_CUSTOM_DTS_PATH="$(BR2_EXTERNAL_ST_PATH)/board/stmicroelectronics/stm32mp1/uboot-dts/*"
BR2_TARGET_UBOOT_CUSTOM_MAKEOPTS="dtb-y=stm32mp157c-dk2-mx.dtb DEVICE_TREE=stm32mp157c-dk2-mx"
```

These options customize the build of U-Boot to use a Device Tree file
produced by STM32 Cube MX, called `stm32mp157c-dk2-mx`. The option
`dtb-y=stm32mp157c-dk2-mx.dtb` has been added to U-boot make options, to
build the external devicetree.

```
BR2_PACKAGE_HOST_GENEXT2FS=y
```

This option enables `genext2fs` tool, to be able to generate *ext4*
partition with `genimage`.

```
BR2_PACKAGE_HOST_RAUC=y
```

This option enables `rauc` tool for the host to generate a RAUC update
bundle.

```
BR2_PACKAGE_M4PROJECTS=y
```

This option enables the installation of the Firmware examples for the Cortex
M4 from [STM32CubeMP1](https://github.com/STMicroelectronics/STM32CubeMP1.git).

## Organization of the `BR2_EXTERNAL` tree

* `board/`
  * `stmicroelectronics/`
    * `stm32mp1/`
      * [`tfa-dts/`](/board/stmicroelectronics/stm32mp1/tfa-dts), Device
        Tree files produced by STM32 Cube MX for TF-A. Only used by
        the demo configurations.
      * [`overlay/`](/board/stmicroelectronics/stm32mp1/overlay/),
        the boot filesytem overlay for the basic configurations. It
        contributes `/boot/extlinux.conf` to the root filesystem to select
        the right devicetree name.
      * [`overlay-demo/`](/board/stmicroelectronics/stm32mp1/overlay-demo/),
        the boot filesytem overlay for the demo configurations. It
        contributes `/boot/extlinux.conf` to the root filesystem to select
        the right devicetree name. It also adds the Wifi firmware, the
        sound configuration files and RAUC configuration files.
      * [`linux-dts/`](/board/stmicroelectronics/stm32mp1/linux-dts),
        Device Tree files produced by STM32 Cube MX for Linux. Only
        used by the demo configurations.
      * [`uboot-dts/`](/board/stmicroelectronics/stm32mp1/uboot-dts),
        Device Tree files produced by STM32 Cube MX for U-Boot. Only
        used by the demo configurations.
      * [`optee-dts/`](/board/stmicroelectronics/stm32mp1/optee-dts),
        Device Tree files produced by STM32 Cube MX for OPTEE-OS. Only
        used by the demo configurations.
      * [`flash.tsv`](/board/stmicroelectronics/stm32mp1/flash.tsv),
        configuration file for the STM32 Cube Programmer. Only valid
        for SD card flashing.
      * [`genimage.cfg`](/board/stmicroelectronics/stm32mp1/genimage.cfg),
        configuration file for the `genimage` utility, which produces
        the final `sdcard.img` SD card image. It describes the
        partition layout of the SD card. Only used by basic configurations.
      * [`genimage-demo.cfg`](/board/stmicroelectronics/stm32mp1/genimage-demo.cfg),
        configuration file for the `genimage` utility, which produces
        the final `sdcard.img` SD card image. It describes the
        partition layout of the SD card. Only used by demo configurations.
      * [`post-build.sh`](/board/stmicroelectronics/stm32mp1/post-build.sh),
        the script executed by Buildroot at the end of the rootfs generation
        to produce update the `extlinux.conf` with the right devicetree name.
      * [`post-build-demo.sh`](/board/stmicroelectronics/stm32mp1/post-build-demo.sh),
        the script executed by Buildroot for demo configuration at the end
        of the rootfs generation. It creates Wifi firmware links, update
        RAUC configurations files and creates `/data` directory.
      * [`post-image.sh`](/board/stmicroelectronics/stm32mp1/post-image.sh),
        the script executed by Buildroot at the end of the build to
        produce the SD card image and deploy the flash.tsv file.
      * [`post-image.sh`](/board/stmicroelectronics/stm32mp1/post-image.sh),
        the script executed by Buildroot for demo configurations at the end
        of the build to produces the RAUC update bundle.
      * [`linux-disable-etnaviv.config`](/board/stmicroelectronics/stm32mp1/linux-disable-etnaviv.config),
        a Linux kernel configuration file fragment that disables the
        Etnaviv GPU driver.
      * [`linux-enable-fbdev-emul.config`](/board/stmicroelectronics/stm32mp1/linux-enable-fbdev-emul.config),
        a Linux kernel configuration file fragment that enables the
        *fbdev* emulation of the DRM subsystem, which is needed on the
        STM32MP135 platform to be able to use the *linuxfb* backend of
        Qt5, in the absence of GPU/OpenGL
      * [`linux-enable-rauc.config`](/board/stmicroelectronics/stm32mp1/linux-enable-rauc.config),
        a Linux kernel configuration file fragment that enables the
        requisite kernel driver to use RAUC.
      * [`patches`](/board/stmicroelectronics/stm32mp1/patches), which
        contains one patch for the Linux kernel, fixing a module
        loading issue for the audio codec driver.
      * [`patches-demo`](/board/stmicroelectronics/stm32mp1/patches-demo),
        which contains one patch for the U-boot Bootloader, adding OTA
        special environment.
* [`package/m4projects`](/package/m4projects), a Buildroot package
  that builds and installs all the Cortex-M4 examples of the
  [STM32CubeMP1](https://github.com/STMicroelectronics/STM32CubeMP1.git)
  sources. It uses a [python
  script](/package/m4projects/parse_project_config.py) as a wrapper to
  transform the .project and .cproject files readable by the dedicated
  [Makefile](/package/m4projects/Makefile.stm32).
* `configs/`
  * [`st_stm32mp157a_dk1_defconfig`](/configs/st_stm32mp157a_dk1_defconfig),
  * [`st_stm32mp157d_dk1_defconfig`](/configs/st_stm32mp157d_dk1_defconfig),
    minimal configurations for the DK1
  * [`st_stm32mp157a_dk1_demo_defconfig`](/configs/st_stm32mp157a_dk1_demo_defconfig),
  * [`st_stm32mp157d_dk1_demo_defconfig`](/configs/st_stm32mp157d_dk1_demo_defconfig),
    demo configurations for the DK1
  * [`st_stm32mp157c_dk2_defconfig`](/configs/st_stm32mp157c_dk2_defconfig),
  * [`st_stm32mp157f_dk2_defconfig`](/configs/st_stm32mp157f_dk2_defconfig),
    minimal configurations for the DK2
  * [`st_stm32mp157c_dk2_demo_defconfig`](/configs/st_stm32mp157c_dk2_demo_defconfig),
  * [`st_stm32mp157f_dk2_demo_defconfig`](/configs/st_stm32mp157f_dk2_demo_defconfig),
    demo configurations for the DK2
  * [`st_stm32mp135f_dk_defconfig`](/configs/st_stm32mp135f_dk_defconfig),
    minimal configurations for the DK
  * [`st_stm32mp135f_dk_demo_defconfig`](/configs/st_stm32mp135f_dk_demo_defconfig),
    demo configurations for the DK
* `docs`, documentation
* `Config.in`, top-level Config.in file mandatory in all `BR2_EXTERNAL`
  trees. Indicate the location of the Config.in file from our `m4projects`
  package.
* `README.md`
* `external.desc`, mandatory in all `BR2_EXTERNAL` trees, gives a name
  and description for the `BR2_EXTERNAL` tree
* `external.mk`, mandatory in all `BR2_EXTERNAL` trees, indicate the
  location of `*.mk` file from new packages.

## Changes compared to upstream Buildroot

The `st/2023.02.10` branch of this `BR2_EXTERNAL` is designed to work
with Buildroot 2023.02.10 However, we needed a few changes compared to
upstream Buildroot 2023.02.10, which can be seen at
[https://github.com/bootlin/buildroot/commits/st/2023.02.10](https://github.com/bootlin/buildroot/commits/st/2023.02.10). We
have just 3 changes on top of Buildroot 2023.02.10, and they can easily
be rebased on top of the latest Buildroot 2023.02.x to continue to
benefit from the security fixes provided by the Buildroot community.

Here are the 3 changes:

* Update the `gcnano-binaries` package to a newer version. This
  package contains the closed-source OpenGL user-space libraries,
  which need to be in sync with the kernel side.

* Fix a regression in the `optee-test` package by backporting two
  patches from upstream OP-TEE.

* Fix the build of TF-A fip tool in the `arm-trusted-firmware` package.
  This patch has been cherry picked from Builroot mainline.