[Bug 2128161] Re: pi-kernel VC4-KMS not working with CM5

Tue Mar 3 20:29:13 UTC 2026

We are beginning to include Pi 5 units in our digital signage deployment
that is built on Ubuntu Core 24 and ubuntu-frame using a mix of
amd64/arm64 devices. We ran into this issue when using Pi 5. We've
automated the workaround from juergh in post #5 using a systemd service
and a script. The service automates the fix after a kernel
update+reboot. Testing ok for us so far.

pi5-display-fix.service:
```
[Unit]
Description=Ensure Pi 5 Display Overlay is Correct
After=snapd.service

[Service]
Type=oneshot
ExecStart=/bin/bash /home/ubuntu/pi5-display-fix.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
```

pi5-display-fix.sh:
```
#!/bin/bash

echo "Checking Raspberry Pi 5 Long-Path Overlay status..."
#  find the newest pi-kernel snap directory
KERNEL_DIR=$(ls -d /boot/piboot/pi-kernel_*.snap | sort -V | tail -n 1)

if [ -z "$KERNEL_DIR" ]; then
    echo "Error: Could not find pi-kernel directory in /boot/piboot/"
    exit 1
fi

# Check if fix is already applied for this kernel
if [ -f "$KERNEL_DIR/overlays/vc4-pi5.dtbo" ] && grep -q "dtoverlay=vc4-pi5" /run/mnt/ubuntu-seed/config.txt; then
    echo "Fix already applied for active kernel ($KERNEL_DIR)."
    exit 0
fi

echo "New kernel detected or fix missing. Applying fix to: $KERNEL_DIR"

# 1. Copy the overlay to the shortened name
sudo cp "$KERNEL_DIR/overlays/vc4-kms-v3d-pi5.dtbo" "$KERNEL_DIR/overlays/vc4-pi5.dtbo"

# 2. Update config.txt
sudo sed -i 's/dtoverlay=vc4-fkms-v3d,cma-128/dtoverlay=vc4-pi5/' /run/mnt/ubuntu-seed/config.txt
sudo sed -i 's/dtoverlay=vc4-kms-v3d-pi5/dtoverlay=vc4-pi5/' /run/mnt/ubuntu-seed/config.txt

echo "Fix applied! Rebooting..."
sleep 5
sudo reboot
exit 0

```

...in case anyone else needs an automated way around this until the bug is fixed.

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https://bugs.launchpad.net/bugs/2128161

Title:
  pi-kernel VC4-KMS not working with CM5

Status in canonical-kernel-snaps:
  Invalid
Status in linux-raspi package in Ubuntu:
  Invalid
Status in rpi-eeprom package in Ubuntu:
  Confirmed

Bug description:
  Hello!

  After switching from PI4B to CM5 on core24 stopped working vc4 driver.
  PiOS (trixie) working with CM5 too.

  On Raspberry Pi 4B by sudo dmesg | grep vc4:

  [ 3.496362] vc4-drm gpu: bound fe400000.hvs (ops vc4_hvs_ops [vc4])
  [ 3.500184] rc rc0: vc4-hdmi-0 as /devices/platform/soc/fef00700.hdmi/rc/rc0
  [ 3.500322] input: vc4-hdmi-0 as /devices/platform/soc/fef00700.hdmi/rc/rc0/input0
  [ 3.506345] input: vc4-hdmi-0 HDMI Jack as /devices/platform/soc/fef00700.hdmi/sound/card0/input1
  [ 3.507075] vc4-drm gpu: bound fef00700.hdmi (ops vc4_hdmi_ops [vc4])
  [ 3.512241] rc rc1: vc4-hdmi-1 as /devices/platform/soc/fef05700.hdmi/rc/rc1
  [ 3.512368] input: vc4-hdmi-1 as /devices/platform/soc/fef05700.hdmi/rc/rc1/input2
  [ 3.518685] input: vc4-hdmi-1 HDMI Jack as /devices/platform/soc/fef05700.hdmi/sound/card1/input3
  [ 3.518919] vc4-drm gpu: bound fef05700.hdmi (ops vc4_hdmi_ops [vc4])
  [ 3.519244] vc4-drm gpu: bound fe004000.txp (ops vc4_txp_ops [vc4])
  [ 3.519461] vc4-drm gpu: bound fe206000.pixelvalve (ops vc4_crtc_ops [vc4])
  [ 3.519618] vc4-drm gpu: bound fe207000.pixelvalve (ops vc4_crtc_ops [vc4])
  [ 3.519762] vc4-drm gpu: bound fe20a000.pixelvalve (ops vc4_crtc_ops [vc4])
  [ 3.519870] vc4-drm gpu: bound fe216000.pixelvalve (ops vc4_crtc_ops [vc4])
  [ 3.520029] vc4-drm gpu: bound fec12000.pixelvalve (ops vc4_crtc_ops [vc4])
  [ 3.527520] [drm] Initialized vc4 0.0.0 20140616 for gpu on minor 0
  [ 3.528322] vc4-drm gpu: [drm] Cannot find any crtc or sizes
  [ 3.530767] vc4-drm gpu: [drm] Cannot find any crtc or sizes
  [ 3.531094] vc4-drm gpu: [drm] Cannot find any crtc or sizes

  On Compute module 5 vc4 not loading (sudo dmesg | grep vc4 empty, sudo
  dmesg | grep fb):

  [ 7.050579] bcm2708_fb soc:fb: Unable to determine number of FBs. Disabling driver.
  [ 7.058623] bcm2708_fb: probe of soc:fb failed with error -2

  Two boards have (snap list):

  Name Version Rev Tracking Publisher Notes
  console-conf 24.04.1+git45g5f9fae19+g7598200 80 24/stable canonical** -
  core24 20250829 1197 latest/stable canonical** base
  mesa-2404 24.2.8-snap185 917 latest/stable canonical** -
  pi 24-3 151 24/stable canonical** gadget
  pi-kernel 6.8.0-1039.43 1047 24/stable canonical** kernel
  snapd 2.71 25205 latest/stable canonical** snapd
  ubuntu-frame 211-mir2.20.1 12494 24/stable canonical** -

  Linux kernel:

  Linux localhost 6.8.0-1039-raspi #43-Ubuntu SMP PREEMPT_DYNAMIC Tue
  Sep 9 12:15:05 UTC 2025 aarch64 aarch64 aarch64 GNU/Linux

  config.txt:

  dtoverlay=vc4-kms-v3d

  Is there a solution to make VC4-KMS work on core24?

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