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i.MX8M Mini Boot issue-UART4

Question asked by Shruthi Subramanian on Jul 26, 2019
Latest reply on Jul 29, 2019 by igorpadykov



We are doing i.MX8M Mini based custom Board bring up.

The UART4 is used as debug UART in our custom board, with this we are getting SPL and ATF debug prints, but U-boot debug prints are not getting.

If we configure UART2 as debug UART in our custom board (both SW and HW), the U-boot prints are coming in debug console.

1)Is there any limitation for debug UART that only UART2 must be configured for debug console? Please clarify.


2)For your your information ,following changes are made to configure UART4 as debug console. Please Confirm this is correct.


  1. File Name: “include/configs/imx8mm_evk.h”



  1. DTSI and DTS file changes


aliases {


serial3 = &uart4;




        uart4: serial@30a60000 {

                compatible = "fsl,imx8mm-uart",

                             "fsl,imx6q-uart", "fsl,imx21-uart";

                reg = <0x0 0x30a60000 0x0 0x10000>;

                interrupts = <GIC_SPI 29 IRQ_TYPE_LEVEL_HIGH>;

                interrupt-parent = <&gpc>;

                clocks = <&clk IMX8MM_CLK_UART4_ROOT>,

                        <&clk IMX8MM_CLK_UART4_ROOT>;

                clock-names = "ipg", "per";

                status = "disabled";




        chosen {

                bootargs = "console=ttymxc3,115200 earlycon=ec_imx6q,0x30a60000,115200";

                stdout-path = &uart4;



iomux configureation


                pinctrl_uart4: uart3grp {

                        fsl,pins = <

                                MX8MM_IOMUXC_UART4_RXD_UART4_DCE_RX     0x49

                                MX8MM_IOMUXC_UART4_TXD_UART4_DCE_TX     0x49





&uart4 { / console /

        pinctrl-names = "default";

        pinctrl-0 = <&pinctrl_uart4>;

        status = "okay";



  1. File name: “board/freescale/imx8mm_evk/imx8mm_evk.c”

static iomux_v3_cfg_t const uart_pads[] = {






Please support and guide us for this issue.


Thanks and Regards,

Shruthi Subramanian