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IMX8 mini UART4

Question asked by David Vescovi on Oct 1, 2019
Latest reply on Oct 10, 2019 by Diego Adrian Cuevas

I have been trying to enable UART4 on our iMX8m Mini board.

I have read all the docs and reviewed other post concerning UART4 on the mini.

None help.


I would like to pin mux pad B8 and E6 which in the standard configuration are:

ECSPI2_MOSI and ECSPI2_SCLK to be used as UART4 TX and RX.

This looks like a valid configuration from all I have read.

I see the fsl-imx8mm.dtsi the following for UART4:

 uart4: serial@30a60000 {
  compatible = "fsl,imx8mq-uart",
        "fsl,imx6q-uart", "fsl,imx21-uart";
  reg = <0x0 0x30a60000 0x0 0x10000>;
  interrupts = <GIC_SPI 29 IRQ_TYPE_LEVEL_HIGH>;
  clocks = <&clk IMX8MM_CLK_UART4_ROOT>,
   <&clk IMX8MM_CLK_UART4_ROOT>;
  clock-names = "ipg", "per";
  dmas = <&sdma1 28 4 0>, <&sdma1 29 4 0>;
  dma-names = "rx", "tx";
  status = "disabled";


The compatible line seems to be in error so I changed it to:

  compatible = "fsl,imx8mm-uart",
        "fsl,imx6q-uart", "fsl,imx21-uart";


I then added the following to the &iomuxc in my .dts file:


pinctrl_uart4: uart4grp {
 fsl,pins = <

&uart4 {
 pinctrl-names = "default";
 pinctrl-0 = <&pinctrl_uart4>;
 assigned-clocks = <&clk IMX8MM_CLK_UART4_SRC>;
 assigned-clock-parents = <&clk IMX8MM_SYS_PLL1_80M>;
 status = "okay";


When I boot the kernel crashes with a panic.

If I go back and set status = "disabled" it boots but no UART4.


I suspect I missed some clock enable or something but I can't figure out what.


any help?