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

[Juerg Haefliger]

I believe this is a regression in the Pi 5 bootloader. The overlay
pathname must not be longer than 63 characters, otherwise the overlay
isn't loaded. On core with pi-kernel 1047, the resulting pathname of the
vc4-kms-v3d-pi5 overlay is '/piboot/ubuntu/pi-
kernel_1047.snap/overlays/vc4-kms-v3d-pi5.dtbo` which is one character
too long. Ugg.

Can you copy the overlay to vc4-pi5.dtbo and use 'dtoverlay=vc4-pi5' in
config.txt and confirm vc4 is working? Note that this modification
obviously only works on Pi 5.

** Also affects: rpi-eeprom (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: canonical-kernel-snaps
       Status: New => Invalid

** Changed in: linux-raspi (Ubuntu)
       Status: Confirmed => Invalid

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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:
  New

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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