I am using Ka-ro qs8m-mq00 qsbase2 board. Also I am learning Yocto. I am not an Yocto specialist, I’m just learning this topic, so I have some beginner’s troubles.
I faced troubles with SPI and I2C customizing like changes some pins etc. As far as I understand, I need to create my own .dts file that includes existing .dts (in my case imx8mm-qs8m-mq00.dts ?).
Unfortunatelly, I can not find some clear tutorial with this process description. There are some pieces of information about patch files creations, some .bbappend examples etc. But I have not found some step-by-step explanation. It looks like I am near the correct solution, but I can not obtaing image with this customized device tree.

Could you help with this? Could you provide some steps description? Or, probably, there is some clear instruction that I have not found?

Thanks in advance!

So, I created some spitest recipe that will produce image for bitbake spitest-image image generation. This is some “hello, world” C++ application with CMake usage.
Directory structure is as follows:

├── COPYING.MIT
├── README
├── conf
│   └── layer.conf
├── readme.md
└── recipes-spitest
    ├── images
    │   └── spitest-image.bb
    └── spitest
        ├── files
        │   ├── CMakeLists.txt
        │   ├── main.cpp
        │   └── spitest.dts
        └── spitest_1.0.bb

conf/layer.conf:

# We have a conf and classes directory, add to BBPATH
BBPATH .= ":${LAYERDIR}"

# We have recipes-* directories, add to BBFILES
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb 
            ${LAYERDIR}/recipes-*/*/*.bbappend"

BBFILE_COLLECTIONS += "spitest"
BBFILE_PATTERN_spitest = "^${LAYERDIR}/"
BBFILE_PRIORITY_spitest = "6"

LAYERDEPENDS_spitest = "core"
LAYERSERIES_COMPAT_spitest = "mickledore"

recipes-spitest/images/spitest-image.bb:

SUMMARY = "spitest image"

require ../../meta-karo-distro/recipes-core/images/karo-image-minimal.bb

IMAGE_INSTALL:append = " spitest"

recipes-spitest/spitest/files/spitest.dts

// SPDX-License-Identifier: (GPL-2.0 OR MIT)
/*
 * Copyright (C) 2019 Lothar Waßmann <[email protected]>
 *
 */

/dts-v1/;

#include "imx8mm-qs8m-mq00.dts"

/ {
    model = "Ka-Ro electronics QS8M-MQ00 (NXP i.MX8MM) module on QSBASE2 baseboard";

// Some changes
};

recipes-spitest/spitest/spitest_1.0.bb

SUMMARY = "bitbake-layers recipe"
LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

DESCRIPTION = "This is spitest image."

SRC_URI = "
    file://CMakeLists.txt 
    file://main.cpp 
    file://spitest.dts 
    "

S = "${WORKDIR}"

KERNEL_DEVICETREE:append = " spitest.dtb"

inherit pkgconfig cmake

do_install() {
    install -d ${D}${bindir}
    install -m 0755 ${B}/spitest ${D}${bindir}/spitest
}

I tried to make some error in spitest.dts, but bitbake didn’t generate any error message. So, spitest.dts is not compiled and not spitest.dtb generated.
Is it possible neither use patches nor change source dts files?