1. Article purpose
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
The device tree binding documents are stored in the given applicable components listed:
- OP-TEE OS:
- Calibration device tree bindings for STM32MP13x lines
and STM32MP15x lines : documentation/devicetree/bindings/clock/st,stm32-calibration.yaml - Calibration device tree bindings for STM32MP2 series: documentation/devicetree/bindings/clock/st,stm32mp25-rcc.yaml (see hsi-calibration and msi-calibration subnodes).
- Calibration device tree bindings for STM32MP13x lines
3. DT configuration
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)
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
By default, Timer12 is the counter used by both HSI/CSI calibration node at SoC level.
3.1.2. STM32MP15x lines
By default, Timer15 is the counter used by both HSI/CSI calibration node at SoC level.
3.1.3. STM32MP2 series
STM32MP2 series doesn't need to reserve a counter for HSI/MSI calibration, the flexclkgen engine is offering the capability to calculate the frequency of any internal clock via an internal module called clock frequency calculator.
3.2. DT configuration (board level)
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, each oscillator calibration (HSI/CSI/MSI) is disabled. It must be explicitly enable at board level.
3.3. DT configuration examples
Here is an example for CSI calibration activation for STM32MP1 series:
&csi_calibration {
status = "okay";
};
Here is an example for HSI calibration activation with a counter update for STM32MP1 series:
&hsi_calibration {
counter = <&timers15 0 7>;
status = "okay";
};
Here is an example of MSI calibration DT configuration for STM32MP2 series:
&msi_calibration {
status = "okay";
};
4. How to configure the DT using STM32CubeMX
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
Refer to the following links for additional information: