Re: [PATCH iwl-net] e1000e: fix flow control stuck off after link partner reset

[Matt Vollrath <tactii@gmail.com>]

On 9/23/26 19:58, Craig I. Hagan wrote:
> On an I219 (pch_spt+) copper with jumbo MTU enabled, a link partner
> reset (e.g. a switch reboot) can leave the PHY's pause advertisement
> bits dropped. Nothing re-asserts them on link-up, so every renegotiation
> resolves flow control to none. rx_crc_errors climb and traffic stalls until
> the interface is manually reset. Observed on I219-LM (8086:15b7) at
> MTU 9000 behind a switch that was power-cycled.
> 
> In the watchdog, detect a completed autonegotiation that resolved
> to no flow control despite pause being requested and the pause bits
> missing from the advertisement, and schedule reset_task to rebuild
> the advertisement (as ethtool -r does). Remediation is limited to three
> attempts, 30s apart, until the next link down.
> 
> Remediate via the existing reset path rather than re-asserting the
> advertisement on link-up; a root-cause rework can follow in net-next.
> 
> Fixes: 79849ebc0e06 ("e1000e: initial support for i219")
> Cc: stable@vger.kernel.org
> Link: https://github.com/systemd/systemd/issues/25925
> Assisted-by: LLM
> Signed-off-by: Craig I. Hagan <hagan@amazon.com>
> ---
I was able to repro this on an I219-LM laptop by link cycling with MEI
runtime PM enabled while the NIC runtime PM was disabled.

At 1500 MTU flow control still doesn't end up in the right state, but
traffic otherwise flows normally. I don't think traffic is stalling
because flow control is off, I think it's stalling because
e1000_lv_jumbo_workaround_ich8lan didn't run after the PHY reset.

I didn't try your patch, but there's a four line fix. Where the watchdog
resets just the PHY when the MAC exits DMoff state, set FLAG_RESTART_NOW
instead of resetting the PHY, then goto link_up. This works for me at
both 1500 and 9000 MTU.

If runtime PM were enabled on your NIC it would reset anyway and avoid
this error.

See:

https://lore.kernel.org/netdev/20190628224932.3389-16-jeffrey.t.kirsher@intel.com/