How to configure TF-A BL2

1. Article purpose[edit source]

This section details the TF-A BL2 stage (Trusted Firmware-A Boot Loader stage 2) used as FSBL (First Stage Boot Loader). It explains how to configure and build BL2 in STM32 MPU context, describes the build process from sources, and shows how to deploy it on your target.

2. Source code access and build process[edit source]

2.1. Cross compilation[edit source]

Cross compilation of TF-A BL2 is only required if it needs to be modified.
Refer to Setup Cross compile environment.

The build process creates an STM32 image. This binary is built in a single step during the build process.

2.2. Install sources[edit source]

2.2.1. From the Developer package[edit source]

The Developer Package contains OpenSTLinux and TF-A sources: TF-A Installation

2.2.2. Official source tree[edit source]

Download the source code from the official Trusted Firmware-A git repository.

  git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git

Warning

The STM32MP1 platform is not yet fully upstreamed. Depending on the version used, some features may not be available.

For a full-featured software, go to STMicroelectronics github:

  git clone https://github.com/STMicroelectronics/arm-trusted-firmware.git

2.2.3. Distribution Package[edit source]

It is possible to use the distribution package to download and rebuid TF-A BL2

2.3. Build process[edit source]

2.3.1. TF-A Build flags[edit source]

Here is the list of the mandatory flags that need to be specified to complete the TF-A BL2 build:

ARM_ARCH_MAJOR = 7: the major version of Arm architecture to target (STM32MP1 is based on an Arm v7 architecture)
ARCH = aarch32: specifies aarch32 architecture to be built
PLAT = stm32mp1: builds an STM32MP1 platform
DTB_FILE_NAME = <fdt file name>.dtb: this flag must be defined to build the proper target and include the correct DTB file into the final file
The boot device(s) you use, one (or several) of:
- STM32MP_EMMC = 1
- STM32MP_SDMMC = 1
- STM32MP_RAW_NAND = 1
- STM32MP_SPI_NAND = 1
- STM32MP_SPI_NOR = 1
or a programming interface:
- STM32MP_UART_PROGRAMMER = 1
- STM32MP_USB_PROGRAMMER = 1

Optional flags:

TRUSTED_BOARD_BOOT = 1: Enable Secure boot authentication

Warning

TRUSTED_BOARD_BOOT requires to have first downloaded The MBEDLTS^[1] source code aligned version as specify in TF-A prerequisites ^[2].
MBEDTLS_DIR=<path_to_mbedtls_directory> must be used to compile.

BUILD_PLAT = <folder>: custom output folder name (by default build/<debug/release>/)
DEBUG = 1: adds debug information in all binaries
V = 1: prints verbose compilation traces
DYN_DISABLE_AUTH = 1: enables/disables authentication using device tree
STM32MP_FORCE_MTD_START_OFFSET = <value>: overrides the default start offset to read FIP on MTD devices (need to be aligned with FlashLayout).

Information

Default offsets are STM32MP_NOR_FIP_OFFSET = 0x00080000 and STM32MP_NAND_FIP_OFFSET = 0x00200000

STM32MP_USE_EXTERNAL_HEAP = 1: can be enabled to define MBEDTLS heap out of BL2 sources (defined in device tree).

For ecosystem release ≤ v3.0.0 compatibility

It is still possible to generate the a single BL2/BL32 file without FIP support, an option flag is available:

STM32MP_USE_STM32IMAGE=1: Disable the FIP load and authentication management. Use the STM32 binary load and authentication used in ecosystem release ≤ v3.0.0 .

2.4. Build command[edit source]

The BL2 generation depends on the selected storage device. By default, only one storage device is supported.

Warning

The DTB_FILE_NAME flag and the selected storage must be set to select the correct board configuration.

The device tree file for the target must be located in fdts folder (<board>.dts)

First add your own environment flags:

  unset LDFLAGS;
  unset CFLAGS;

Then compile the TF-A BL2.

The default build command for STM32MP15 is

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 \
         <Selected storage> DTB_FILE_NAME=<board_name>.dtb

Here are build commands for the stm32mp157c-ev1 board (which supports different storage devices):

Flash programming support

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_USB_PROGRAMMER=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb
  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_UART_PROGRAMMER=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

Dedicated boot storage

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_SDMMC=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_EMMC=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_RAW_NAND=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_SPI_NOR=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

Not available on board

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 STM32MP_SPI_NAND=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

Enable Secure boot on SDCard

  MBEDTLS_DIR=<path_to_mbedtls_directory> make ARM_ARCH_MAJOR=7 \
         ARCH=aarch32 PLAT=stm32mp1 TRUSTED_BOARD_BOOT=1 STM32MP_SDMMC=1 \
         DTB_FILE_NAME=stm32mp157c-ev1.dtb

2.5. Final image[edit source]

The final image is available for Flash memory or SDCard update in the corresponding folder:

<BUILD_PLAT>/tf-a-<board>.stm32
Ex:
build/release/tf-a-stm32mp157c-ev1.stm32

3. Updating the software on board[edit source]

3.1. Partitioning of binaries[edit source]

The TF-A build provides a binary named tf-a-<board>.stm32 that MUST be copied to a dedicated partition named "fsblX" (X depends on the number of needed backups in the Flash).

Warning

TF-A must be located in the first partition of your boot device.

You can just update the first partition for a simple test, but all backup partitions must contain the same image at the end.

3.2. Updating via SDCard[edit source]

If you use an SDCard, simply update TF-A using the dd command on your host.
Plug your SDCard into the computer and copy the binary to the dedicated partition; on an SDCard/USB disk the "fsbl1" partition is partition 1:

 - SDCard: /dev/mmcblkXp1 (where X is the instance number)
 - SDCard via USB reader: /dev/sdX1 (where X is the instance number)

Under Linux^®

  dd if=<tf-a file>.stm32 of=/dev/<device partition> bs=1M conv=fdatasync

Information

To find the partition associated to a specific label, just plug the SDCard/USB disk into your PC and call the following command:

  ls -l /dev/disk/by-partlabel/
 total 0
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 bootfs -> ../../mmcblk0p4
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 fip -> ../../mmcblk0p3
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 fsbl1 -> ../../mmcblk0p1          ? FSBL1 (TF-A)
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 fsbl2 -> ../../mmcblk0p2          ? FSBL2 (TF-A backup ? same content as FSBL)
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 rootfs -> ../../mmcblk0p5
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 userfs -> ../../mmcblk0p6

Under Windows^®

CoreUtils ^[3] that includes the dd command is available for Windows.

3.3. Updating via USB mass storage on U-boot[edit source]

See How to use USB mass storage in U-Boot.

Refer to the previous section to put tf-a-<board>.stm32 into SDCard/USB disk.

3.4. Updating your boot device via STM32CubeProgrammer[edit source]

Refer to the STM32CubeProgrammer documentation to update your target.

4. Secure secret provisioning (SSP)[edit source]

A specific TF-A BL2 build is required to manage SSP.

Warning

This STM32 output file must be signed to complete the SSP feature.

Dedicated files are delivered in the platform folder that contains the specific Makefile and bl2_plat_setup for the TF-A SSP.
The TF-A SSP is a subset of the standard TF-A BL2 that includes only:

BL2 device tree
BL2 image with limited support to the serial link device.

4.1. Additional flags[edit source]

The mandatory flags to build the TF-A SSP are:

STM32MP_SSP = 1

For the serial link (exclusive):

STM32MP_UART_PROGRAMMER = 1
STM32MP_USB_PROGRAMMER = 1

4.2. Build command[edit source]

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 \
         STM32MP_SSP=1 STM32MP_USB_PROGRAMMER=1 \
         DTB_FILE_NAME=<board>.dtb

or

  make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 \
         STM32MP_SSP=1 STM32MP_UART_PROGRAMMER=1 \
         DTB_FILE_NAME=<board>.dtb

4.3. Final image[edit source]

The final image is available in the corresponding folder:

tf-a-ssp-<board>.stm32
For example:
tf-a-ssp-stm32mp157c-ev1.stm32

[1] ttps://github.com/ARMmbed/mbedtls

[2] ttps://trustedfirmware-a.readthedocs.io/en/v2.4/getting_started/prerequisites.html

[3] ttp://gnuwin32.sourceforge.net/packages/coreutils.htm

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