Debian on downstream kernel Part 1

Instructions for running Debian on a Raspberry Pi OS (RpiOS) kernel.

2025-08-08 Motivation

Debian is my distro of choice (after using various distros for decades.) The Raspberry Pi 5 has a new I/O subsystem based on the RP1 chip and which requires significant S/W modifications to run Linux. These have not yet been fully upstreamed such that Debian can boot and run on a Pi 5 (as of kernel version 6.16.)

2025-08-08 Overview

  1. Install Debian using a Pi 4B (or CM4) on the target storage. This example will use an NVME SSD. A previous proof-of-concept was tested using a USB connected SATA SSD.
  2. Build the kernel per instructions kindly provided at https://www.raspberrypi.com/documentation/computers/linux_kernel.html. This can be done on the Pi 4B/CM4 (hours) or cross built on a more powerful host (minutes.)
  3. Install the kernel, modules and related files (DTBs) to the target media.
  4. Boot the Pi 5 from the target media.

2025-08-08 Details

The desired target media is an NVME SSD and the development platform is a Ryzen 7 7700X based host running Debian Bookworm. The storage will be connected to the Ryzen host using a USB/NVME housing and to the Pi 5 using the Waveshare NVME HAT+. The target OS will be Debian Trixie (which will see release as Stable tomorrow.) The most recent kernel branch at https://github.com/raspberrypi/linux is rpi-6.12.y and that will be used for this process.

2025-08-08 Prep

Pull kernel code and install required build tools.

mkdir -p ~/Downloads/pi-kernel
cd ~/Downloads/pi-kernel
git clone --depth=1 --branch rpi-6.12.y https://github.com/raspberrypi/linux
sudo apt install bc bison flex libssl-dev make libc6-dev libncurses5-dev
sudo apt install crossbuild-essential-arm64

Set environment variables

CONFIG_LOCALVERSION="-v8-for-Deb-X"
KERNEL=kernel_2712

2025-08-08 Build [^1]

cd ~/Downloads/pi-kernel/linux
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bcm2712_defconfig
time -p make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- Image modules dtbs

2025-08-08 Prepare target

Using Ansible playbooks. The result did not boot from a CM4. This procedure will proceed with the target as provisioned and prior to the first boot. Any preferred method of provisioning the target media should work.

2025-08-08 Copy to target media

Identify the device, in this case /dev/sdb and mount accordingly:

cd ~/Downloads/pi-kernel/linux
mkdir -p mnt/boot
mkdir -p mnt/root
sudo mount /dev/sdb1 mnt/boot
sudo mount /dev/sdb2 mnt/root
sudo mkdir -p mnt/boot/overlays

Install modules to target:

sudo env PATH=$PATH make -j1$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- INSTALL_MOD_PATH=mnt/root modules_install

Install the kernel

sudo cp mnt/boot/$KERNEL.img mnt/boot/$KERNEL-backup.img
sudo cp arch/arm64/boot/Image mnt/boot/$KERNEL.img
sudo cp arch/arm64/boot/dts/broadcom/*.dtb mnt/boot/
sudo cp arch/arm64/boot/dts/overlays/*.dtb* mnt/boot/overlays/
sudo cp arch/arm64/boot/dts/overlays/README mnt/boot/overlays/

Edit the target config.txt to specify the correct kernel:

sudo vim mnt/boot/config.txt # or editor of your choice

Unmount the target device partitions.

sudo umount mnt/boot
sudo umount mnt/root

Install the NVME SSD in the NVME HAT_ and boot the system. (Great Success!) At this point the process is complete and the user can proceed however they wish to complete the installation

Further customization is peformed using Ansible Playbooks.

Note: Following first boot playbook the host no longer boots. This requires further investigation.

2025-08-12 try using Sid

Plan

  1. Install the Trixie image to an NVME SSD (in a USB enclosure) (Using Ansible playbook.)
  2. Move the SSD to a CM4 with PCIe/NVME board.
  3. Boot and upgrade using Ansible playbook and complete configuration.
  4. Edit sources.list and upgrade to Sid.
  5. Return card to USB enclosure and install downstream kernel.
  6. Install card in Pi 5 and boot.

2025-08-13 build newer kernel

Checking out https://github.com/raspberrypi/linux/tags it seems that the branch I was using is old. It seems like the most recent stable tag is worth a try as well.

mkdir -p ~/Downloads/pi-kernel
cd ~/Downloads/pi-kernel
time -p git clone --branch stable_20250702 --depth=1 https://github.com/raspberrypi/linux

Set environment variables

CONFIG_LOCALVERSION="-v8-for-Deb-20250702-X"
KERNEL=kernel_2712

2025-08-13 Build

make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bcm2712_defconfig
time -p make -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- Image modules dtbs

Follow Sid install and configuration Install using USB enclosure on X86_64 host (olive.)

2025-08-13 Copy to target media

Return the USB/NVME enclosure to the cross build host. Identify the device, in this case /dev/sdb and mount accordingly:

cd ~/Downloads/pi-kernel/linux
mkdir -p mnt/boot
mkdir -p mnt/root
sudo mount /dev/sdb1 mnt/boot
sudo mount /dev/sdb2 mnt/root
sudo mkdir -p mnt/boot/overlays

Install modules to target:

sudo env PATH=$PATH make -j1$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- INSTALL_MOD_PATH=mnt/root modules_install

Install the kernel

sudo cp mnt/boot/$KERNEL.img mnt/boot/$KERNEL-backup.img
sudo cp arch/arm64/boot/Image mnt/boot/$KERNEL.img
sudo cp arch/arm64/boot/dts/broadcom/*.dtb mnt/boot/
sudo cp arch/arm64/boot/dts/overlays/*.dtb* mnt/boot/overlays/
sudo cp arch/arm64/boot/dts/overlays/README mnt/boot/overlays/

Edit the target config.txt to specify the correct kernel:

sudo vim mnt/boot/config.txt # or editor of your choice

Unmount the target device partitions.

sudo umount mnt/boot
sudo umount mnt/root

Move the USB enclosure to the Pi 5 and boot. Host comes up.

Comment out upstream_kernel=1 in config.txt and reboot. Host comes up and is running:

hbarta@kweli:~$ uname -a
Linux kweli 6.12.34-v8-16k+ #2 SMP PREEMPT Wed Aug 13 10:59:11 CDT 2025 aarch64 GNU/Linux
hbarta@kweli:~$

Add dtparam=pciex1 and consider adding dtparam=pciex1_gen=3. Shutdown and move SSD to NVME HAT. Pi 5 boots.

Heed the warning in config.txt:

# If you need to set boot-time parameters, do so via the
# /etc/default/raspi-firmware, /etc/default/raspi-firmware-custom or
# /etc/default/raspi-extra-cmdline files.

vim /etc/default/raspi-firmware /etc/default/raspi-firmware-custom

Upgrade (one package parted) and reboot. Now go for KDE/Plasma 

apt install kde-plasma-desktop # 1329 packages.

Completes and on checking config.txt I find

root@kweli:~# cat /boot/firmware/config.txt 
# Do not modify this file!
#
# It is automatically generated upon install or update of either the
# firmware or the Linux kernel.
#
# If you need to set boot-time parameters, do so via the
# /etc/default/raspi-firmware, /etc/default/raspi-firmware-custom or
# /etc/default/raspi-extra-cmdline files.

# Switch the CPU from ARMv7 into ARMv8 (aarch64) mode
arm_64bit=1

enable_uart=1
upstream_kernel=1

kernel=vmlinuz-6.12.41+deb13-arm64
# For details on the initramfs directive, see
# https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=10532
initramfs initrd.img-6.12.41+deb13-arm64

# Inserted by /etc/default/raspi-firmware-custom

# raspi-firmware-custom
dtparam=pciex1
kernel=kernel_2712.img
root@kweli:~#

I will add upstream_kernel=0 to /etc/default/raspi-firmware-custom (and edit it that way now.) systemctl start sddm did not work. No login screen.

root@kweli:~# systemctl start sddm
root@kweli:~# systemctl status sddm
● sddm.service - Simple Desktop Display Manager
     Loaded: loaded (/usr/lib/systemd/system/sddm.service; enabled; preset: enabled)
     Active: active (running) since Wed 2025-08-13 12:00:41 CDT; 11s ago
 Invocation: 61ed8c0fb0bc4c01a9148618a7860c4f
       Docs: man:sddm(1)
             man:sddm.conf(5)
   Main PID: 33731 (sddm)
      Tasks: 2 (limit: 9549)
        CPU: 43ms
     CGroup: /system.slice/sddm.service
             └─33731 /usr/bin/sddm

Aug 13 12:00:41 kweli systemd[1]: Started sddm.service - Simple Desktop Display Manager.
Aug 13 12:00:41 kweli sddm[33731]: Initializing...
Aug 13 12:00:41 kweli sddm[33731]: Starting...
Aug 13 12:00:41 kweli sddm[33731]: Logind interface found
root@kweli:~#

No joy on reboot. Fails on pinctrl_lookup_state.

2025-10-18 having another go at this

See https://hankb.github.io/MkDocs-blog/tech/Debian_on_downstream_kernel.02/

notes

  • [^1] @ukleinek on IRC suggested make bindeb-pkg to produce a .deb for the modules. This will be convenient when building a new kernel on the Pi 5 but is less so when cross developing on another host.