1. Article purpose[edit source]
The purpose of this article is to explain how to configure the OP-TEE Calibration service using the device tree mechanism, relying on the bindings documentation, that is the description of the required and optional device-tree properties.
2. DT bindings documentation[edit source]
The device tree binding documents are stored in the given applicable components listed:
- OP-TEE OS:
- Calibration device tree bindings: documentation/devicetree/bindings/clock/st,stm32-calibration.yaml
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 organization.
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/SoC level)[edit source]
The Calibration node is located in the device tree file for the software components, supporting the peripheral and listed in the above DT bindings documentation paragraph.
3.1.1. STM32MP13x lines 
[edit source]
By default, Timer12 is the counter used by both HSI/CSI calibration node at SoC level.
3.1.2. STM32MP15x lines [edit source]
By default, Timer15 is the counter used by both HSI/CSI calibration node at SoC level.
3.2. DT configuration (board level)[edit source]
The objective of this chapter is to explain how to enable and configure the calibration DT nodes for a board.
Configuration should be done in specific board device tree files (board dts file).
By default, both HSI/CSI calibration are disabled. It must be explicitly enable at board level.
3.3. DT configuration examples[edit source]
Here is an example for CSI calibration activation:
&csi-calibration {
status = "okay";
};
Here is an example for HSI calibration activation with a counter update:
&hsi-calibration {
counter = <&timers15 0 7>;
status = "okay";
};
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 DT binding files listed in the above DT bindings documentation paragraph. If so, the tool inserts user sections in the generated device tree. These sections can then be edited to add some properties, and they are preserved from one generation to another. Refer to STM32CubeMX user manual for further information.
5. References[edit source]
Refer to the following links for additional information: