FDCAN device tree configuration

Article purpose

This article explains how to configure the FDCAN when it is assigned to the Linux^® OS. In that case, it is controlled by the CAN framework for Bosch M_CAN controller.

The configuration is performed using the device tree mechanism that provides a hardware description of the FDCAN peripheral, used by the M_CAN Linux driver and by the NET/CAN framework.

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

DT bindings documentation

M_CAN device tree bindings describe all the required and optional properties.

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 split.

STM32CubeMX can be used to generate the board device tree. Refer to How to configure the DT using STM32CubeMX for more details.

DT configuration (STM32 level)

All M_CAN nodes are described in stm32mp157c.dtsi file with disabled status and required properties such as:

• Physical base address and size of the device register map
• Message RAM address and size (CAN SRAM)
• Host clock and CAN clock
• Message RAM configuration

This is a set of properties that may not vary for a given STM32 device.

 m_can1: can@4400e000 {
 	compatible = "bosch,m_can";                       
 	reg = <0x4400e000 0x400>, <0x44011000 0x1400>;    /* FDCAN1 uses only the first half of the dedicated CAN_SRAM */
 	reg-names = "m_can", "message_ram";
 	interrupts = <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>,
 		     <GIC_SPI 21 IRQ_TYPE_LEVEL_HIGH>;
 	interrupt-names = "int0", "int1";
 	clocks = <&rcc CK_HSE>, <&rcc FDCAN_K>;
 	clock-names = "hclk", "cclk";
 	bosch,mram-cfg = <0x0 0 0 32 0 0 2 2>;
 	status = "disabled";
 };
 
 m_can2: can@4400f000 {
 	compatible = "bosch,m_can";
 	reg = <0x4400f000 0x400>, <0x44011000 0x2800>;    /* The 10 Kbytes of the CAN_SRAM are mapped */
 	reg-names = "m_can", "message_ram";
 	interrupts = <GIC_SPI 20 IRQ_TYPE_LEVEL_HIGH>,
 		     <GIC_SPI 22 IRQ_TYPE_LEVEL_HIGH>;
 	interrupt-names = "int0", "int1";
 	clocks = <&rcc CK_HSE>, <&rcc FDCAN_K>;
 	clock-names = "hclk", "cclk";
 	bosch,mram-cfg = <0x1400 0 0 32 0 0 2 2>;         /* Set mram-cfg offset to write FDCAN2 data on the second half of the dedicated CAN_SRAM */
 	status = "disabled";
 };

The required and optional properties are fully described in the bindings files.

This device tree part is related to STM32 microprocessors. It must be kept as is, without being modified by the end-user.

DT configuration (board level)

Part of the device tree is used to describe the FDCAN hardware used on a given board. The DT node ("m_can") must be filled in:

• Enable the CAN block by setting status = "okay".
• Configure the pins in use via pinctrl, through pinctrl-0 (default pins), pinctrl-1 (sleep pins) and pinctrl-names.

DT configuration examples

The example below shows how to configure and enable FDCAN1 instance at board level:

 &m_can1 {
 	pinctrl-names = "default", "sleep";         /* configure pinctrl modes for m_can1 */
 	pinctrl-0 = <&m_can1_pins_a>;               /* configure m_can1_pins_a as default pinctrl configuration for m_can1 */
 	pinctrl-1 = <&m_can1_sleep_pins_a>;         /* configure m_can1_sleep_pins_a as sleep pinctrl configuration for m_can1 */
 	status = "okay";                            /* enable m_can1 */ 
 };

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.
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.

References

Please refer to the following links for additional information:

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