How to setup an own device tree for a RaspberryPI in yocto? - raspberry-pi

Question

I like to disable and enable some pins in my RPi project.
These are GPIO 6, GPIO 5 and GPIO 26. I like to use these PINs in my own kernel driver.
For this project I connect a simple electric board via the GPIOs. The minimal system is build via yocto. I like to change the device tree file to disable/enable GPIOs.
I need to change or make my own dts file. For that I think I will need to:
find the original RPi dts
patch it or create my own dts
add it to the layer.conf
add file to the kernel recipe via append
How can I do this? or where can I find the sources?
Actually I am struggling to find the dts files for the RPi2 I am using. I was checking the "raspberrypi2-poky-linux-gnueabi" recipe results(and do not find any files).
I do not find any tutorial how to setup yocto + meta-raspberrypi + own dts. it would be great if we can figure out the necessary steps.

Answer 1

I'm not convinced this question has been well answered, so let me take a few minutes and document what I've done to add device tree overlays to my yocto builds.
This is a multi-problem process.
I'm going to make a few assumptions:
* You source your oe-init-build-env in a shell, and do your bitbake builds manually in a terminal (or you know how to do it with equivalent tooling)
* You know (or are already learning) the basics of device trees...
Start with your own meta layer. Mine is out on github.
You'll need to create an *-overlay.dts source file. You can start with a simple place holder, and stuff it (quite literally) anywhere on your system. We'll import it to your meta layer in the next step using bitbake to do some of the staging and what-not for us.
recipetool appendsrcfile -wm rpi /path/to/your-layer-meta virtual/kernel /path/to/your-overlay.dts 'arch/${ARCH}/boot/dts/overlays/your-overlay.dts
At this point, you should end up with a recipes-kernel/linux directory with an appropriate bbappend targeting the $MACHINE type of -wm (rpi, as above), ready to copy the device tree source file into the proper spot for bitbake to find it when it building the kernel. But it still won't be included in your kernel build.
We need to add the overlay reference to the KERNEL_DEVICETREE variable, in places that will cover the scopes of: linux, bootfiles, and the sdcard_image-rpi.bbclass from meta-raspberrypi.
In the linux bbappend created in step 3, add KERNEL_DEVICETREE += "overlays/your-overlay.dtbo" to make the linux kernel build include your dts as something to compile into a dtbo.
To make the sdcard_image-rpi.bbclass copy the file, you'll need to add KERNEL_DEVICETREE =+ "overlays/your-overlay.dtbo" to your image recipe.
To make the overlay active, you'll need to create a recipes-bsp/bootfiles/rpi-config_git.bbappend whereyou can append a do_deploy step to add the dtoverlay=your line to config.txt.
I use my layer for more than one project, so I felt OK with having the dts compile with every kernel but only copy it to images where my image recipe added it to the KERNEL_DEVICETREE. For further insurance that I don't get these things interferring in images I don't want them in, my rpi-config append has a test to see if I should add the dtoverlay line to the config.txt
Of course, this was all assuming you were going to use your own home-grown DTS without starting from a kernel-sourced one. The process would be largely the same, but you'd be able to patch the existing, or copy it, or whatever you want to do in your linux recipe.
I hope this helps! I know it's an old question.

Answer 2

First you need to find the kernel used on your yocto project, the recipe is linux-raspberry.bb or something like linux-*.bb. The preferred kernel is probably set in your local.conf or machine.conf: PREFERRED_PROVIDER_virtual/kernel ?= "linux-raspberry"
This is indirectly set via "meta-raspberrypi/conf/machine/include/rpi-default-providers.inc" which is included via "rpi-base.inc"
Once found, take a look at the recipe, clone the git repository of the kernel, on the right branch, and reset at the right SRCREV.
Once downloaded, the dts files are in /path/of/my/kernel/linux-raspberry/arch/arm/boot/dts/. You can find the name of the devicetree file used in the kernel recipe, local.conf or machine.conf, with the variable KERNEL_DEVICETREE = "..."
For the meta-raspberry and rpi2 selected, the dts files can be found in <path to build dir>/linux-raspberrypi2-standard-build/source/arch/arm/boot/dts/. The source dir is a linked dir to the git sources.
You can add a new dtb by creating dtsi/dts files (don't forget to add it in the Makefile).
Create a patch, add it to the kernel recipe:
SRC_URI += "file://0001-mypatch.patch"
and put the patch file like this in your meta
├── files
│   └── 0001-mypatch.patch
└── linux-raspberry.bb
Modify the KERNEL_DEVICETREE variable to add your new dtb.
Now you can bitbake your kernel/image, your new dtb will be created.