Raspberry Pi (RPI): How to Install a New Kernel

Tutorial Assumptions

For simplicity’s sake, this tutorial will assume that you already read How to cross-compile your kernel with kw and How to Install a New Kernel. If not, get back here later; we will wait for you :)

Anyway, we also assume the following tasks are completed:

  • You already compiled your kernel

  • You have a working .config file

  • You will use remote deploy. Remember, to deploy remotely, you need to have root access to the target machine via ssh.

  • All commands in this tutorial must be executed inside a kernel tree. If you want to work with Raspberry Pi, use this repository <https://github.com/raspberrypi/linux>.

We also assume that you have a Raspberry Pi (RPI) with Rasbian (it could be 32 or 64 bits), but keep in mind that the steps described here are generic, and we just decided to focus on this device to have a way to provide some practical examples.

DTB file and kworkflow.config

Some architectures require Device Tree Binary (dtb) and Device Tree Binary Overlay (dtbo) files, and Raspberry Pi falls into this category. We usually need to add these files in a specific location for a functional boot. For example, in the case of RPI 4 32 bits, it should be under the /boot folder, and for RPI 4 64 bits, it is /boot/broadcom. However, these locations may vary, so we need to tell kw how to handle these files, but don’t worry, this is a trivial task. Open your .kw/deploy.config and search for:

dtb_copy_pattern=

Use this parameter to configure how kw will handle the dtb files. You have three different options:

1. Empty: It will assume *.dtb, which means that kw will copy all dtb files to the target /boot folder. For example, RPI 4 32 bits requires this option.

2. Folder pattern: You can specify something like dtb_copy_pattern=broadcom/*, which means kw will copy all dtb files inside the broadcom folder. This is the required option for RPI 4 64 bits.

3. Multiple folder copy: Finally, you can tell kw that you want to copy multiple folders by using a pattern like this dtb_copy_pattern=broadcom,rockchip,arm.

As you can see, kw is really flexible about handling the dtb files.

Use a default kw config template for RPI

For RPI developers, kw provides some useful templates that already setup your config in a convenient way. If you want to deploy your kernel for an RPI 32 bits, you can use the following template:

kw init --template=rpi4-raspbian-32-cross-x86-arm

Or if you want to deploy your kernel to an RPI 4 64 bits, you can use:

kw init --template=rpi4-raspbian-64-cross-x86-arm

Build and deploy

Note

The RPI needs to keep the modules after they are installed, so to have a proper deploy on the RPI is ideal to set strip_modules_debug_option=no on .kw/deploy.config.

At this point, we suppose that you already compiled your kernel and added a very cool suffix name to your image. Additionally, we presume that your target is a machine that you have ssh access as root. For now, you can run the glorious build and deploy:

kw bd

Other kw deploy features

Remember that kw deploy provides many other features to handle your custom kernel. For example, if you want to list all custom kernels that you installed in your system, just use:

kw deploy --list

Or if you want to remove some specific kernel:

kw deploy --uninstall KERNEL_NAME

Keep in Mind

In this tutorial, we used RPI 4 as a use case in order to make some of the new concepts more practical. Nevertheless, you should be able to setup kw to handle dtb files that need to be deployed in various ways. Finally, if this step does not work in your custom system, consider improving kw to support your target system workflow; patches are always welcome.