1. Article purpose[edit source]
The purpose of this article is to explain how to configure the RCC internal peripheral clocks using the device tree mechanism, relying on the bindings documentation, that is the description of the required and optional device-tree properties.
The peripheral can be assigned to different contexts/software components, depending on the final product needs. Refer to How to assign an internal peripheral to a runtime context article for guidelines on this configuration .
2. DT bindings documentation[edit source]
The device tree binding documents are stored either in the given applicable components listed below, or in the Linux kernel repository:
- TF-A BL2:
- for STM32MP13x lines
docs/devicetree/bindings/clock/st,stm32mp13-rcc.txt - for STM32MP15x lines docs/devicetree/bindings/clock/st,stm32mp1-rcc.txt
- for STM32MP13x lines
- OP-TEE:
- for STM32MP13x lines documentation/devicetree/bindings/clock/st,stm32mp13-rcc.yaml
- for STM32MP13x lines
- U-Boot, Linux® OS:
- for example: STM32MP1x device tree bindings: Documentation/devicetree/bindings/clock/st,stm32mp1-rcc.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 STM32MP1 RCC node is located
See the example of STM32MP1 RCC clock DT node above in this article, with compatible = "st,stm32mp1-rcc-secure". The node specifies its dependency on the input clock using SCMI clock phandles scmi_clk.
rcc: rcc@50000000 {
compatible = "st,stm32mp1-rcc-secure", "st,stm32mp1-rcc", "syscon";
reg = <0x50000000 0x1000>;
#clock-cells = <1>;
#reset-cells = <1>;
clock-names = "hse", "hsi", "csi", "lse", "lsi";
clocks = <&scmi_clk CK_SCMI_HSE>,
<&scmi_clk CK_SCMI_HSI>,
<&scmi_clk CK_SCMI_CSI>,
<&scmi_clk CK_SCMI_LSE>,
<&scmi_clk CK_SCMI_LSI>;
};
3.2. DT configuration (board level)[edit source]
The objective of this chapter is to explain how to configure a clock tree related to the board.
Using this chapter, the end-user can configure any
parameters via the DT to adapt to a new board.
Clock tree configuration it's only done in TF-A and in OP-TEE.
Usually a minimal configuration is applied in TF-A BL2 and a full configuration in OP-TEE.
This an example a clock configuration tree:
&rcc {
compatible = "st,stm32mp13-rcc", "syscon", "st,stm32mp13-rcc-mco";
pinctrl-0 = <&rcc_mco_pins_a>;
pinctrl-names = "default";
st,clksrc = <
CLK_MPU_PLL1P
CLK_AXI_PLL2P
CLK_MLAHBS_PLL3
CLK_RTC_LSE
CLK_MCO1_HSE
...
>;
st,clkdiv = <
DIV(DIV_MPU, 1)
DIV(DIV_AXI, 0)
DIV(DIV_MLAHB, 0)
...
>;
st,pll_vco {
pll3_vco_417_8Mhz: pll3-vco-417_8Mhz {
src = < CLK_PLL3_HSE >;
divmn = < 1 33 >;
frac = < 0x1a04 >;
};
pll4_vco_600Mhz: pll4-vco-600Mhz {
src = < CLK_PLL4_HSE >;
divmn = < 1 49 >;
};
};
/* VCO = 417.8 MHz => P = 209, Q = 24, R = 11 */
pll3:st,pll@2 {
compatible = "st,stm32mp1-pll";
reg = <2>;
st,pll = < &pll3_cfg1 >;
pll3_cfg1: pll3_cfg1 {
st,pll_vco = < &pll3_vco_417_8Mhz >;
st,pll_div_pqr = < 1 16 36 >;
};
};
/* VCO = 600.0 MHz => P = 50, Q = 10, R = 50 */
pll4:st,pll@3 {
compatible = "st,stm32mp1-pll";
reg = <3>;
st,pll = < &pll4_cfg1 >;
pll4_cfg1: pll4_cfg1 {
st,pll_vco = < &pll4_vco_600Mhz >;
st,pll_div_pqr = < 11 59 11 >;
};
};
};
You can find a full example of the board configuration here stm32mp135f-dk.dts
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]
Please refer to the following links for additional information: