Last edited 7 months ago

DCMI device tree configuration

Applicable for STM32MP15x lines

1 Article purpose[edit source]

This article explains how to configure the DCMI internal peripheral when assigned to the Linux® OS. In that case, it is controlled by the V4L2 camera framework.

The configuration is performed using the device tree mechanism that provides a hardware description of the DCMI peripheral, used by the STM32 DCMI Linux driver or by the V4L2 camera framework.

If the peripheral is assigned to another execution context, refer to How to assign an internal peripheral to an execution context article for guidelines on peripheral assignment and configuration.

2 DT bindings documentation[edit source]

The DCMI internal peripheral is documented through the STM32 DCMI device tree bindings file[1].

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 article 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 DCMI device tree node is declared in stm32mp151.dtsi [2].

The declaration (shown below) provides the hardware registers base address, interrupts, reset line, clocks and dma channel used.

		dcmi: dcmi@4c006000 {
			compatible = "st,stm32-dcmi";
			reg = <0x4c006000 0x400>;
			interrupts = <GIC_SPI 78 IRQ_TYPE_LEVEL_HIGH>;
			resets = <&rcc CAMITF_R>;
			clocks = <&rcc DCMI>;
			clock-names = "mclk";
			dmas = <&dmamux1 75 0x400 0xe0000001>;
			dma-names = "tx";
			status = "disabled";
Warning white.png Warning
This device tree part is related to STM32 microprocessors. It must be kept as is, without being modified by the end-user.

When using a different sensor camera device, only the sensor-related configuration part must be adapted in the associated board devicetree file (see #DT configuration (board level)).

DCMI capture performance can be increased by relying on a 2nd DMA channel and SRAM located intermediate buffer in order to achieve DMA / MDMA chaining. DCMI driver is configured to achieve this by giving a 2nd dma channel entry and a sram pool phandle into the dcmi node. Such configuration is done in the board DT, the following section gives such example.

Refer to stm32-dcmi bindings[1] for more details.

3.2 DT configuration (board level)[edit source]

&sram4 {
	dcmi_pool: dcmi_pool@0 {
		reg = <0x0 0x8000>;

&dcmi {
	status = "okay";
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&dcmi_pins_a>;
	pinctrl-1 = <&dcmi_sleep_pins_a>;
	/* Enable DMA-MDMA chaining by adding a SRAM pool and a MDMA channel */
	sram = <&dcmi_pool>;
	dmas = <&dmamux1 75 0x400 0x01>, <&mdma1 0 0x3 0x1200000a 0 0>;
	dma-names = "tx", "mdma_tx";
port {
		dcmi_0: endpoint {
			remote-endpoint = <&ov5640_0>;
			bus-type = <5>;
			bus-width = <8>;
			hsync-active = <0>;
			vsync-active = <0>;
			pclk-sample = <1>;
			pclk-max-frequency = <77000000>;

This section, part of the STM32MP15 evaluation board device tree file[3], shows how is configured the DCMI hardware block to interconnect with the sensor camera device. In this example, DMA-MDMA chaining is enabled by allocating a buffer area within the SRAM and updating the dmas property of the dcmi node to indicate both DMA and MDMA channels. The configurable settings are the following:

  • Camera sensor endpoint: in this case, the Omnivision OV5640 model[4].
  • Bus width: 8, 10, 12 or 14 bits
  • Horizontal synchronization line level: active low (0) or active high (1)
  • Vertical synchronization line level: active low (0) or active high (1)
  • Pixel clock polarity line level: active low (0) or active high (1)
  • Pixel clock maximum frequency in Hertz

This section also defines what is the DCMI pins multiplexing used for this board (<&dcmi_pins_a>, <&dcmi_sleep_pins_a>), exact pins details being defined in the STM32MP15 evaluation board pinctrl device tree file[5]:

			dcmi_pins_a: dcmi-0 {
				pins {
					pinmux = <STM32_PINMUX('H', 8,  AF13)>,/* DCMI_HSYNC */
						 <STM32_PINMUX('B', 7,  AF13)>,/* DCMI_VSYNC */
						 <STM32_PINMUX('A', 6,  AF13)>,/* DCMI_PIXCLK */
						 <STM32_PINMUX('H', 9,  AF13)>,/* DCMI_D0 */
						 <STM32_PINMUX('H', 10, AF13)>,/* DCMI_D1 */
						 <STM32_PINMUX('H', 11, AF13)>,/* DCMI_D2 */
						 <STM32_PINMUX('H', 12, AF13)>,/* DCMI_D3 */
						 <STM32_PINMUX('H', 14, AF13)>,/* DCMI_D4 */
						 <STM32_PINMUX('I', 4,  AF13)>,/* DCMI_D5 */
						 <STM32_PINMUX('B', 8,  AF13)>,/* DCMI_D6 */
						 <STM32_PINMUX('E', 6,  AF13)>,/* DCMI_D7 */
						 <STM32_PINMUX('I', 1,  AF13)>,/* DCMI_D8 */
						 <STM32_PINMUX('H', 7,  AF13)>,/* DCMI_D9 */
						 <STM32_PINMUX('I', 3,  AF13)>,/* DCMI_D10 */
						 <STM32_PINMUX('H', 15, AF13)>;/* DCMI_D11 */

			dcmi_sleep_pins_a: dcmi-sleep-0 {
				pins {
					pinmux = <STM32_PINMUX('H', 8,  ANALOG)>,/* DCMI_HSYNC */
						 <STM32_PINMUX('B', 7,  ANALOG)>,/* DCMI_VSYNC */
						 <STM32_PINMUX('A', 6,  ANALOG)>,/* DCMI_PIXCLK */
						 <STM32_PINMUX('H', 9,  ANALOG)>,/* DCMI_D0 */
						 <STM32_PINMUX('H', 10, ANALOG)>,/* DCMI_D1 */
						 <STM32_PINMUX('H', 11, ANALOG)>,/* DCMI_D2 */
						 <STM32_PINMUX('H', 12, ANALOG)>,/* DCMI_D3 */
						 <STM32_PINMUX('H', 14, ANALOG)>,/* DCMI_D4 */
						 <STM32_PINMUX('I', 4,  ANALOG)>,/* DCMI_D5 */
						 <STM32_PINMUX('B', 8,  ANALOG)>,/* DCMI_D6 */
						 <STM32_PINMUX('E', 6,  ANALOG)>,/* DCMI_D7 */
						 <STM32_PINMUX('I', 1,  ANALOG)>,/* DCMI_D8 */
						 <STM32_PINMUX('H', 7,  ANALOG)>,/* DCMI_D9 */
						 <STM32_PINMUX('I', 3,  ANALOG)>,/* DCMI_D10 */
						 <STM32_PINMUX('H', 15, ANALOG)>;/* DCMI_D11 */

An alternate pin multiplexing could be defined (for example to fit a new board design) by modifying the STM32MP15 evaluation board pinctrl device tree file[5] following the possible pins assignment defined in the MPU reference manual[6].

STM32CubeMX [7] pins configurator is of great help to find valid alternatives thanks to its visual GUI.

Refer to STM32 DCMI bindings[1] for more details.

3.3 DT configuration examples[edit source]

	ov5640: camera@3c {
		compatible = "ovti,ov5640";
		reg = <0x3c>;
		clocks = <&clk_ext_camera>;
		clock-names = "xclk";
		DOVDD-supply = <&v2v8>;
		powerdown-gpios = <&stmfx_pinctrl 18 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
		reset-gpios = <&stmfx_pinctrl 19 (GPIO_ACTIVE_LOW | GPIO_PUSH_PULL)>;
		rotation = <180>;
		status = "okay";

		port {
			ov5640_0: endpoint {
				remote-endpoint = <&dcmi_0>;
				bus-width = <8>;
				data-shift = <2>; /* lines 9:2 are used */
				hsync-active = <0>;
				vsync-active = <0>;
				pclk-sample = <1>;
				pclk-max-frequency = <77000000>;

This section, part of the STM32MP15 evaluation board device tree file[3], enables the support of the OV5640 Omnivision camera sensor[4] located on the MB1379 camera daughter board[8] connected to the CN7 camera connector[9] of the STM32MP15 evaluation board[10].

Refer to the OV5640 bindings [4] for more details.

Documentation on various V4L2 camera sensors can be found inside I2C media bindings folder[11]. Refer to the dedicated sensor binding documentation to adapt your board devicetree file to this dedicated sensor.

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.
The STM32CubeMX may not support all the properties described 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: