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

[Dave Jones]

I've now verified resolute (26.04) still boots and reboots on a Pi 4, Pi
5, and a Pi 500 on SD, NVMe, and SSD, and that the A/B mechanism still
works with them. Hence, I'm proceeding with the resolute upload -- will
work on the questing and noble SRUs once that's migrated.

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Title:
  [SRU][FFe] 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:
  Triaged
Status in linux-raspi source package in Noble:
  Invalid
Status in rpi-eeprom source package in Noble:
  Confirmed
Status in linux-raspi source package in Questing:
  Invalid
Status in rpi-eeprom source package in Questing:
  Confirmed

Bug description:
  [ Impact ]

  On Pi 5 (and CM5 by extension), the current EEPROM-based bootloader
  does not support the long paths required by Ubutu Core, with the
  result that video output fails (see comments 12 and 13 below for
  example of path length).

  Given that the bootloader is a binary blob within this package, we
  need to do a full version bump to incorporate the new bootloader,
  hence the FFe (for resolute) and SRU (for questing and noble).

  [ Test plan ]

  As this will affect the bootloader on the Pi 4 and Pi 5, we must test
  boot and reboot functionality on all affected models, for all
  supported boot media, as well as the video functionality that
  originated the report.

  For each affected $model (Pi 4, 400, CM4, Pi 5, 500, CM5) on each
  affected $series (noble, questing, resolute) for each supported boot
  $media (SD, USB MSD, NVMe (pi5 only)):

  * Flash Ubuntu $series to a spare $media device
  * Boot the $media device on the affected $model
  * Let cloud-init finish and login
  * Run sudo rpi-eeprom-update and confirm current EEPROM date is earlier than 2025-12-08 (pi5) or 2026-01-09 (pi4) and no update is available (if EEPROM is current, deliberately downgrade with sudo rpi-eeprom-update -f <date> and reboot to install)
  * Enable proposed pocket
  * sudo apt install $series-proposed rpi-eeprom
  * Run sudo rpi-eeprom-update and confirm update *is* available (to dates given above)
  * Run sudo rpi-eeprom-update -a and reboot to install update
  * Ensure system boots normally afterward (check both cold and warm boots)

  On questing and resolute only:

  * sudo flash-kernel
  * sudo reboot
  * If system comes back up normally this demonstrates the A/B boot functionality still operates correctly under the new EEPROM

  To test video functionality (Pi 5, CM5 only):

  * Flash Ubuntu Core 24 to a spare SD card
  * On Pi 5 and CM5 (lite), boot SD card and let the first time setup run
  * Ensure video output works correctly
  * Switch config.txt on boot partition from vc4-fkms-v3d to vc4-kms-v3d
  * Reboot and ensure video output still works correctly

  [ Where things could go wrong ]

  Fiddling with the bootloader EEPROM always carries the serious risk of
  breaking boot on some supported model in some supported boot mode.
  Hence, the comprehensive test plan covering all affected boards and
  boot media, in addition to covering the original issue.

  [ Original report ]

  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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