Pi 5: continuous Ethernet link flapping since EEE enabled by default in rpi-6.18.y (#7270), mostly with AVM Fritz!Box link partners

[agners]

Note: The report below was largely generated with AI assistance. I have read through it to verify that the claims are accurate and reflect what our users report in the Home Assistant OS issue tracker.

Describe the bug

Since Home Assistant OS moved from a rpi-6.12.y based kernel to rpi-6.18.y, we have received multiple reports of Raspberry Pi 5 devices whose onboard Ethernet link flaps continuously:

macb 1f00100000.ethernet end0: Link is Down
macb 1f00100000.ethernet end0: Link is Up - 1Gbps/Full - flow control off

This repeats every few seconds (in some cases starting within seconds after boot), with packet loss towards the default gateway and effectively unusable networking. Rolling back to the 6.12-based OS release restores a stable link on identical hardware, cabling and switch port.

Setting dtparam=eee=off resolves the problem on 6.18. This has been confirmed by three affected users, one of them with a full on/off/on cycle: flapping with EEE enabled, stable for two days with it disabled, flapping returned after re-enabling.

Disabling EEE on the link partner side also resolves the flapping: confirmed on Fritz!Box 7490 and 7590 (LAN port energy setting changed from "automatic" to "none") and on managed switches that offer an EEE toggle. Partners without such an option keep flapping unless EEE is disabled on the Pi.

Our 6.12-based releases used rpi-6.12.y at 89050b1, which still contained the eee-broken-1000t/eee-broken-100tx properties from #6900 — EEE was never negotiated there. rpi-6.18.y enables EEE by default on the RP1 GEM since #7270 (macb EEE/TX LPI support, BCM54213PE switched from AutogrEEEn to native EEE mode, eee_enabled_default = true with a 250 ms TX LPI timer; earlier testing round in #7251). This matches the observed behavior change exactly.

Affected setups (from our issue tracker)

Four users have reported the link flapping so far, one more with the same hardware combination is holding back the update in anticipation. Where the direct link partner is known:

• AVM Fritz!Box 7590 — three users (at least two directly connected, no switch in between)
• One of the four reproduced the flapping against a whole range of devices: TP-Link TL-SG608E, TP-Link TL-SG1016DE, TP-Link ER605, Netgear GS105NA, Fritz!Box 7490 and Fritz!Box 7590. This user verified the link behavior (LAN LED fully down and back up in ~5 s intervals, matching the dmesg pattern above) and confirmed that disabling EEE on either side — the Pi or a partner that offers an EEE setting — stops the flapping, while unmanaged partners without an EEE option keep flapping until EEE is disabled on the Pi.

AVM Fritz!Box devices are clearly overrepresented as link partner, but the last report suggests the problem is not limited to a single vendor's LPI handling: on that Pi, every EEE-capable partner tested triggered the flapping.

For scale: we have roughly 100 000 Raspberry Pi 5 installations on 6.18-based OS releases, so the overall incidence is low — most link partners appear to handle the newly negotiated EEE fine.

Environment

• Raspberry Pi 5 Model B (one confirmed Rev 1.1, revision d04171)
• Kernels: rpi-6.18.y 6.18.33 (stable_20260527) and 6.18.34 (stable_20260609)
• Not reproducible on rpi-6.12.y (6.12.75, which contains the dts: cm5/pi5: Disable EEE on rp1 #6900 DT workaround)

Steps to reproduce

1. Raspberry Pi 5 with an affected link partner (e.g. Fritz!Box 7590), rpi-6.18.y kernel with default EEE configuration
2. Boot and run dmesg | grep "Link is" — the link flaps every few seconds
3. Add dtparam=eee=off to config.txt and reboot — the link is stable

Additional context

• Symptom-wise this resembles the Raspberry Pi 4 / bcmgenet situation after EEE was enabled there (Rpi4 loses network connectivity via eth0 after kernel update to 6.18.24 #7365): a broad, vendor-diverse set of link partners affected, resolved by Pi-side fixes ([RPi4-bcmgenet] regression: EEE reporting/dtparam support broken (EEE always enabled) #7372, net: phy: honor eee_disabled_modes in phy_support_eee() #7373, net: bcmgenet: keep RBUF EEE/PM disabled #7388) rather than by blaming partner equipment. We have not ruled out either direction for the Pi 5 yet — partner devices mishandling LPI vs. marginal TX LPI signaling from the RP1 GEM.
• Downstream reports: HAOS 18 regression: Ethernet link flapping on Raspberry Pi 5 after upgrading to HAOS 18.0 / 18.1 home-assistant/operating-system#4861, Raspberry Pi 5: HAOS 18.1 causes repeated Ethernet link up/down events, packet loss and unstable network (17.3 is stable) home-assistant/operating-system#4881

Device(s)

Raspberry Pi 5

System

Home Assistant OS 18.0/18.1 (rpi-6.18.y 6.18.33 / 6.18.34, stable_20260527 / stable_20260609)

[nbuchwitz]

Does the behavior change with a lower / higher lpi timer value?