Public bug reported:
Distribution: Ubuntu 26.04.1 LTS (Resolute)
Package: linux-raspi
Kernel version: 7.0.0-1017-raspi
Image: ubuntu-26.04.1-preinstalled-server-arm64+raspi.img.xz
Image SHA256: d59ef9c6e85b906995501f166d00726ab80b59be7b65cdeac0fa31b996053e13
---
SUMMARY
On a Raspberry Pi 4 Model B Rev 1.4 (8GB), the kernel hangs during boot at
xhci_hcd (VL805) initialization (~2.6 seconds in). The hardware watchdog then
resets the board, causing an infinite reboot loop.
This behavior only triggers if the EEPROM boot order attempts a network
boot prior to falling back to the SD card. If the default boot order is
used, the exact same image on the exact same board boots successfully to
userspace.
---
HARDWARE MATRIX & DIFFERENTIAL DIAGNOSIS
- Pi 4B Rev 1.4 (8GB, Board ID: d03114) + BOOT_ORDER=0xf12 -> HANGS & LOOPS
(3/3 attempts)
- Pi 4B Rev 1.4 (8GB, Board ID: d03114) + BOOT_ORDER=0xf41 -> BOOTS SUCCESSFULLY
- Pi 4B Rev 1.1 (2GB, Board ID: b03111) + BOOT_ORDER=0xf12 -> BOOTS SUCCESSFULLY
ENVIRONMENT CONTROLS (Tested on the failing Rev 1.4 board with 0xf12 nightly):
- Ubuntu 24.04.5 (Kernel 6.8.0-1064-raspi): BOOTS SUCCESSFULLY
- Raspberry Pi OS Bookworm/Trixie (Kernel 6.12.109+rpt-rpi-v8): BOOTS
SUCCESSFULLY
The regression is isolated exclusively to the 7.0.0-1017-raspi kernel on
Pi 4 revisions that lack a dedicated physical SPI EEPROM for the VL805
USB controller (where firmware must be side-loaded into controller RAM
by the bootloader). It appears the state of the PCIe endpoint/VL805 is
left in an unhandled state after a failed network boot fallback, which
causes kernel 7.0's xhci_hcd driver to hard lock.
---
EEPROM CONFIGURATION
Bootloader Version: 2026-09-23 (vcgencmd bootloader_version: 2026/09/23
12:02:14)
Config applied to both boards:
BOOT_ORDER=0xf12
DHCP_TIMEOUT=5000
DHCP_REQ_TIMEOUT=500
NET_INSTALL_ENABLED=0
---
STEPS TO REPRODUCE
1. Configure a Pi 4B Rev 1.4 with bootloader 2026-09-23 and BOOT_ORDER=0xf12.
2. Flash a stock ubuntu-26.04.1-preinstalled-server-arm64+raspi.img.xz to an SD
card.
3. Power on the Pi with Ethernet connected, ensuring no active netboot server
answers.
4. Observe the kernel hang at xhci_hcd initialization, followed by a watchdog
reset every ~47 seconds.
5. Change BOOT_ORDER to 0xf41; the board will boot completely normal.
---
HDMI CONSOLE LOG (Last lines prior to watchdog reset)
[ 0.744509] brcm-pcie fd500000.pcie: clkreq-mode set to default
[ 0.746587] brcm-pcie fd500000.pcie: link up, 5.0 GT/s PCIe x1 (SSC)
[ 0.746708] pci 0000:01:00.0: [1106:3483] type 00 class 0x0c0330 PCIe Endpoint
[ 0.746781] pci 0000:01:00.0: BAR 0 [mem 0x00000000-0x00000fff 64bit]
[ 0.746836] pci 0000:01:00.0: ASPM: VL805 fixup applied
[ 0.746905] pci 0000:01:00.0: PME# supported from D0 D3hot
[ 0.748514] pci 0000:01:00.0: ASPM: default states L0s L1 ...
[ 0.776288] printk: legacy console [ttyS0] enabled
[ 2.267371] iproc-rng200 fe104000.rng: hwrng registered
[ 2.271564] vc-mem: phys_addr:0x00000000 mem_base=0x3ec00000
mem_size:0x40000000(1024 MiB)
[ 2.283946] loop: module loaded
[ 2.287469] bcm2835-power bcm2835-power: Broadcom BCM2835 power domains driver
[ 2.295827] bcmgenet fd580000.ethernet: GENET 5.0 EPHY: 0x0000
[ 2.482547] unimac-mdio unimac-mdio.-19: Broadcom UniMAC MDIO bus
[ 2.488726] usbcore: registered new interface driver lan78xx
[ 2.493931] usbcore: registered new interface driver smsc95xx
[ 2.608538] xhci_hcd 0000:01:00.0: xHCI Host Controller
[ 2.613278] xhci_hcd 0000:01:00.0: new USB bus registered, assigned bus number 1
** Affects: linux-raspi (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2172394
Title:
Pi 4B Rev 1.4 hangs at xhci_hcd init / reboot-loops on Ubuntu 26.04
when BOOT_ORDER tries network first
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