@namundsen, @jeremias.tx I think I figured out what I was doing wrong.
I managed to setup toolchain and run linux-toradex repo make on my host PC.
I created fsl-imx8mm-verdin-wifi-dev-m4.dts, add it to Makefile and successfully run
make dtbs. fsl-imx8mm-verdin-wifi-dev-m4.dtb was created.
I decided to compare it to the fsl-imx8mm-verdin-wifi-dev.dtb and
it seems that those two .dtb’s are the same.
I copied it to the Verdin /boot/ostree/torizon-number/dtb/ insted of old fsl-imx8mm-verdin-wifi-dev.dtb
and got rpmsg pingpong example to work.
It seems that 4.14.170-4.0.0-devel+git.62ad468b3107 #1-TorizonCore version that I installed using
EasyInstaller is based on old fsl-imx8mm-verdin.dtsi. I opened dtsi in toradex_4.14-2.3.x-imx branch it up and I found this:
&rpmsg{
/*
* 64K for one rpmsg instance:
* --0xb8000000~0xb800ffff: pingpong
*/
vdev-nums = <1>;
reg = <0x0 0xb8000000 0x0 0x10000>;
status = "okay";
};