How to build device tree changes?

[chillinwithscb]

IMX8M Nano

Yocto build setup from NXP

I want to build a modified device tree for the imx8m nano. I understand the syntax of device tree source files (.dts, dtsi), but I don't know how to get the yocto build to update the DTB: imx8mn-evk.dtb.

I modified imx8mn-evk.dts and built, but my changes do not seem to affect the build. As a test I simply typed garbage into the file and even renamed the file. I expected the build to fail, but no it doesn't. Thing is there's many copies of this file in my build tree. I picked the one under nano/tmp/work-shared/imx8mn-lpddr4-evk/kernel-source/arch/arm64/boot/dts/freescale/ where nano is my build dir. I realize that the files under tmp are only quasi-source files. They come from somewhere else. Maybe modifying them under tmp does not automatically cause the build to see the change. Or I have modified the wrong copy of the file. Or I selected the wrong target to build. I did "bitbake core-image-minimal" thinking that would be good.

IDK whether this is a general yocto issue or something particular to the IMX yocto build. FYI Yocto makes little sense to me in general.

How do I get the yocto build to build changes to the device tree?

[Chavira · Accepted solution]

Hi @chillinwithscb!
Thank you for contacting NXP Support!

You can follow the next posts to solve the problem.

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/How-to-compile-Linux-Kernel-Image-and-de...

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/How-to-use-Devshell-to-compile-device-tr...

Best Regards!

Chavira

[chillinwithscb]

The info in the link How-to-compile-Linux-Kernel-Image-and-device-tree-using-Yocto is good. I actually had already found that info in NXP docs. But it's spread across two docs. The linked article is a more concise and direct description of the steps. 

That said, it was not clear to me from the NXP docs or the article _why_ I'd want to use a standalone build or why it so very complicated to setup. But, I see the value of the standalone build now. And I was able to build an updated DTB.

Thanks.