How can I get linux kernel sources (interested mainly in dts) in Yocto - yocto

Question

I would like to see linux kernel sources that were used to build an image with bitbake in yocto. I need to verify that we are using a correct dts file, and probably to update it.
I was told that devtool can help me to see kernel sources, but I can't understand how to use devtool to get the linux kernel sources(and the dts file in special).
How do I do it?

Answer 1

In order to use devtool to modify the kernel, if you don't know the kernel name, you can execute in the build environment the next command:
devtool modify virtual/kernel
This will modify the recipe for virtual/linux, which underneath is an alias for the kernel you are using, for example linux-tegra, linux-imx, etc.
After you execute that command, you can see the sources that have been unpacked and patched inside your builddir folder on the following path: build/workspace/sources/<kernel recipe name>.
Devtool will create a git repo on that path, which will have the same branches as the remote SRC_URI where it is getting it from, so you can make your changes there.
It will also create a .bbappend so that bitbake knows that the actual source for the kernel is this folder and not the one on tmp. This bbappend is located in this path:
build/workspace/appends/<kernel recipe name>.bbappend
After you modify it, you can just do a bitbake virtual/kernel to build this modified kernel.
In order to find which device tree your machine is using, you can extract such information using the -e flag on bitbake and then grep:
bitbake -e virtual/kernel | grep "^KERNEL_DEVICETREE="
Then you can search for that device tree inside the kernel sources and you can modify it as well.
Hope this helps a little. If you have more doubts let me know.