Hi Ofer
I received answer below:
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There should be no changes to the SCU FW itself. U-Boot (and Linux) make calls to the SCFW API to configure hardware managed by the SCU (i.e., LPUARTs) instead of reading/writing registers directly.
For obvious reasons we'll deal with U-Boot first.
In the board file (for the MEK it's board/freescale/imx8qxp_mek/imx8qxp_mek.c), first make sure UART3 pads are configured in setup_iomux_uart() and clocks are configured an enabled in board_early_init_f(). Searching for (regex) uart.*0 in the board file turns up references in board_quiesce_devices(). Configure CONFIG_SERIAL_LPUART_BASE in your board config file (include/configs/imx8qxp_mek.h for the MEK). There are several environment variables involving the console including boot args passed to the kernel.
Then you'll need to make similar changes in the U-Boot device tree: arch/arm/dts/fsl-imx8qxp*.dts*. MUX and clocks should be configured, though you might need to enable (status = "okay";) lpuart3. Don't forget to include CONFIG_FSL_LPUART=y in your defconfig file.
It might help for you to share with me what you have attempted so far, though it will be difficult for me to help directly unless I can figure out a way to bring out UART3 (or another LPUART) on my MEK. What are the failure symptoms? Just "silence" on the serial line or do you observe U-Boot resets? Do you have a hardware debugger? That makes board bring-up significantly easier.
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so first one can try to change uart0 to uart3 in uboot:
uboot/board/freescale/imx8qxp_mek/imx8qxp_mek.c
imx8qxp_mek.c\imx8qxp_mek\freescale\board - uboot-imx - i.MX U-Boot
use sect.3.3.1 Using JTAG tool for debugging attached Porting Guide.
uart3 example for i.MX8QXP toradex colibri board
colibri-imx8qxp.c\colibri-imx8qxp\toradex\board - u-boot-toradex.git - U-Boot bootloader for Apalis ...
build steps
Build Apalis iMX8/Colibri iMX8X Boot Image/Linux from Scratch
Best regards
igor
