Hi @rudhi.tx ,
As far as the UART goes, I changed the patch to use UART B, which works. So I am convinced that the M4 binary is being loaded and run correctly. I don’t think it’s worth looking into this any further - the important thing is that the M4 code is running.
Then, without touching the U-Boot settings, I’ve replaced the bin file with yours. Just in case there’s any problem I’ve added the colibri-imx8x_disable-cm40-uart_overlay.dtbo.
However, it’s still not working 
torizon@colibri-imx8x-06996015:~$ dmesg | grep -i rpms
[ 0.046741] imx rpmsg driver is registered.
torizon@colibri-imx8x-06996015:~$ sudo modprobe imx_rpmsg_tty
Password:
torizon@colibri-imx8x-06996015:~$ ls /dev/ | grep -i rpms
U-Boot settings :-
torizon@colibri-imx8x-06996015:~$ sudo fw_printenv bootcmd
bootcmd=run m4boot_0; run distro_bootcmd;
torizon@colibri-imx8x-06996015:~$ sudo fw_printenv m4boot_0
m4boot_0=run loadm4image_0; dcache flush; bootaux ${loadaddr} 0
torizon@colibri-imx8x-06996015:~$ sudo fw_printenv loadm4image_0
loadm4image_0=load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${m4_0_image}
torizon@colibri-imx8x-06996015:~$ sudo fw_printenv m4_0_image
m4_0_image=/ostree/deploy/torizon/var/rootdirs/home/torizon/rpmsg_lite_str_echo_rtos.bin
Overlays :-
torizon@colibri-imx8x-06996015:~$ ls /proc/device-tree/chosen/overlays
colibri-imx8x_disable-cm40-uart_overlay.dtbo colibri-imx8x_hmp_overlay.dtbo colibri-imx8x_vga-640x480_overlay.dtbo name
torizon@colibri-imx8x-06996015:~$ cat /proc/device-tree/chosen/overlays/colibri-imx8x_disable-cm40-uart_overlay.dtbo
0torizon@colibri-imx8x-06996015:~$ cat /proc/device-tree/chosen/overlays/colibri-imx8x_hmp_overlay.dtbo
0torizon@colibri-imx8x-06996015:~$ cat /proc/device-tree/chosen/overlays/colibri-imx8x_vga-640x480_overlay.dtbo
0torizon@colibri-imx8x-06996015:~$
modprobe :-
0torizon@colibri-imx8x-06996015:~$ lsmod | grep -i rpmsg
imx_rpmsg_tty 16384 0
So I’m pretty convinced that the problem is on my Linux side. We must have something different.
My tdx-info is the same as above (post #36).
I suppose the next step is to try and diagnose modprobe.
Tim
.
