1. Article purpose[edit source]
The purpose of this article is to explain how to configure the BSEC using the device tree mechanism, that provides a description of the hardware.
2. DT bindings documentation[edit source]
Generic information about NVMEM is available in the NVMEM overview.
The following binding-related documentation explains how to write device tree files for BSEC:
- TF-A: docs/devicetree/bindings/soc/st,stm32-romem.txt"[1]
- Linux® STM32 BSEC devicetree bindings: Documentation/devicetree/bindings/nvmem/st,stm32-romem.txt[2]
- Linux® generic NVMEM devicetree bindings: Documentation/devicetree/bindings/nvmem/nvmem.yaml[3] and Documentation/devicetree/bindings/nvmem/nvmem-consumer.yaml[4]
3. DT configuration[edit source]
This hardware description is a combination of the STM32 microprocessor device tree files (.dtsi extension) and board device tree files (.dts extension). See the Device tree for an explanation of the device-tree file split.
STM32CubeMX can be used to generate the board device tree. Refer to How to configure the DT using STM32CubeMX for more details.
3.1. DT configuration (STM32 level)[edit source]
The BSEC node and NVMEM node are located in the STM32 MPU device tree.
3.2. DT configuration (board level)[edit source]
3.2.1. BSEC node append[edit source]
The board definition in the device tree may include some additional board-specific OTP declarations used in secure world device tree:
&bsec {
board_id: board_id@ec {
reg = <0xec 0x4>;
st,non-secure-otp;
};
};
With only 32 lower NVMEM 32-bit data words, the software needs to manage exceptions in order to allow some upper OTPs to be accessed by the non-secure world, through secure world services for very specific needs. The user can add an OTP declaration in the device tree, using the "st,non-secure-otp" property, with a 32-bit length granularity (that is, 4 bytes).
3.2.2. NVMEM layout node[edit source]
The NVMEM layout node defined in SoC secure device tree gathers all NVMEM platform-dependent layout information, including OTP names and phandles, in order to allow easy access for data consumers, using pre-defined string in the nvmem-cell-names property.
nvmem_layout: nvmem_layout@0 {
compatible = "st,stm32mp1-nvmem-layout";
nvmem-cells = <&cfg0_otp>,
<&part_number_otp>,
<&monotonic_otp>,
<&nand_otp>,
<&uid_otp>,
<&package_otp>,
<&hw2_otp>;
nvmem-cell-names = "cfg0_otp",
"part_number_otp",
"monotonic_otp",
"uid_otp",
"nand_otp",
"package_otp",
"hw2_otp";
};
With this new node, the platform can easily find the OTP numbers, in order to access all the necessary information. This node can be overriden at device tree board level.
4. How to configure the DT using STM32CubeMX[edit source]
The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
STM32CubeMX may not support all the properties described in the documents listed in DT bindings documentation above. If so, the tool inserts user sections in the generated device tree. These sections can then be edited to add some properties that are preserved from one generation to another. Refer to the STM32CubeMX user manual for further information.
5. References[edit source]
Please refer to the following links for additional information: