DSI touchscreen fails to display anything on Pi 5 with Ubuntu Server

[Dave Jones]

Under the Ubuntu 24.04 LTS Server for Raspberry Pi image, with a Pi 5 8GB model (C1 stepping, but worth checking D0 too), the official 7" DSI touchscreen fails to display any output. This is with the stock server configuration, but persists when:

* the KMS overlay is commented out

* disable_fw_kms_setup=1 is commented out

* video=DSI-1:800x480M@60 is prefixed to the kernel command line

(or any combination of the above)

Curiously, the DSI display *does* work under the Desktop image.

We have also attempted installing ubuntu-desktop and ubuntu-raspi-settings-desktop under the Server image with no change, and have verified that the /etc/X11/xorg.conf.d/99-v3d.conf is created, although seemingly *not* with DSI-relevant settings in it because /dev/dri/by-path/*-card does not exist.

This *may* be a kernel issue, but I'm hesitant to believe that given the desktop image (which shares a kernel with the server) *does* work. My current suspicion is that we're missing *something* in the boot configuration, but I'm awaiting delivery of a MIPI-DSI adapter cable to replicate and debug this.

[Dave Jones (waveform)]

Note to self: check oracular and plucky images (both desktop and server) to see if they're equally affected. Also check legacy and updated bootloader variants to see if DSI recognition changes.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dave Jones (waveform)]

Okay, received the DSI adapter cable yesterday. Tested with noble .2 server image [1], and noble .2 desktop image [2] on a Pi 5 8GB (older C1 stepping), and oracular server image [3].

The server image didn't show anything *initially* (rainbow screen or typical initrd output), but midway through systemd starting stuff the screen came on, showing the console output. Logged in normally with an attached keyboard, the screen at least appears to work normally.

The desktop image also didn't show anything until the plymouth boot screen, but then proceeded to work normally through first time setup and for the desktop itself. That said, the ubiquity installer, the snap-store and various things do "fall off the bottom" of the display (clearly not designed for 800x480 resolution!).

To be clear, this is without any modification to the image: config.txt is stock (so KMS overlay is active), as is cmdline.txt (no specification of video=), touchscreen is the official 7" DSI connected display, connected to CSI/DSI port 0, with display's control board powered from the 5V and GND pins on the Pi's header; I'll attach an image of the setup.

[1]: https://cdimage.ubuntu.com/releases/noble/release/ubuntu-24.04.2-preinstalled-server-arm64+raspi.img.xz

[2]: https://cdimage.ubuntu.com/releases/noble/release/ubuntu-24.04.2-preinstalled-desktop-arm64+raspi.img.xz

[3]: https://cdimage.ubuntu.com/releases/oracular/release/ubuntu-24.10-preinstalled-server-arm64+raspi.img.xz

[Dave Jones (waveform)]

Shot of the server noble .2 image operating on the touchscreen (with keyboard attached)

[Dave Jones (waveform)]

Re-tested with the same image on a D0 stepping Pi 5 (2GB model). Same results: console boots happily on server image, desktop works happily too.

I'm afraid for now I'll have to mark this "incomplete" which will automatically close it in a couple of months if nothing new surfaces, but without a way to replicate the issue locally there's not much else I can do.

[Dave Jones (waveform)]

Confirmed this on noble. The root cause is an older boot EEPROM (specifically Dec 2023). On the older firmwares it appears the bootloader pre-allocates a framebuffer with an incorrect resolution for the DSI display, and (on the server images at least), the kernel attempts to re-use this framebuffer which fails. The newer bootloader (tested June 2024, and Dec 2024) honours the disable_fw_kms_setup=1 setting in config.txt, leaving the kernel to handle display setup, which it does correctly.

Ultimately, this is a duplicate of LP: #2085903 which, once it lands, will update the EEPROM image to June 2024. This is already fixed in plucky (devel) which has the later package. Marking accordingly.