UART2 in i.MX8M Plus using DCE/DTE pin can not cross RX / TX as input or output.

[Charlie_Owz]

Hi good morning Community,

We have UART2 multiplexed to the SAI3 pins. Pinmux tool allows to have SAI3_TXC as RX (input) and SAI3_TXFS as TX (output).

When we try the different configuration options, it always uses SAI3_TXC as output.

We have crossed externally the signals and it works with the configuration:

MX8MP_IOMUXC_SAI3_TXC__UART2_DCE_TX        0x00000140

MX8MP_IOMUXC_SAI3_TXFS__UART2_DCE_RX       0x00000140

But we are not able to configure it to use SAI3_TXC as RX (input) and SAI3_TXFS as TX (output).

Is it possible to use the configuration we have in the pinmux? Using SAI3_TXC as input and SAI3_TXFS as output? From the pinmux we understand that yes, from the reference manual we understand that no, but maybe we are missing something...

The options we have to configure are:

1: 

#define MX8MP_IOMUXC_SAI3_TXC__UART2_DCE_TX 0x1C8 0x428 0x000 0x4 0x0 

#define MX8MP_IOMUXC_SAI3_TXFS__UART2_DCE_RX 0x1C4 0x424 0x5F0 0x4 0x4 

2:

#define MX8MP_IOMUXC_SAI3_TXC__UART2_DTE_RX 0x1C8 0x428 0x5F0 0x4 0x5

#define MX8MP_IOMUXC_SAI3_TXFS__UART2_DTE_TX 0x1C4 0x424 0x000 0x4 0x0 

Many thanks in advance!

[BiyongSUN · Accepted solution]

where is the reference manual say no for dte/dce swap?

everything you need is already there. 

lf-5.10.35-2.0.0 as example

1. the pin has definition and the definition already includes the  daisy input

linux/arch/arm64/boot/dts/freescale/imx8mp-pinfunc.h

2. the binding guide for uart 

linux/Documentation/devicetree/bindings/serial/fsl-imx-uart.yaml

  fsl,dte-mode:
    $ref: /schemas/types.yaml#/definitions/flag
    description: |
      Indicate the uart works in DTE mode. The uart works in DCE mode by default.

[Charlie_Owz]

That's right!

We misunderstood that part:

fsl,dte-mode:

Thanks again for your quick answer and your help!