ACK: [SRU][R][PATCH 0/1] igc: Increase Thunderbolt MAC passthrough delay to 1000ms

[Tim Whisonant]

On Wed, Mar 11, 2026 at 03:51:06PM +0800, AceLan Kao wrote:
> From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/2143197
> 
> [Impact]
> Dell Thunderbolt dock ethernet (Intel I226 NIC) can fail to initialize after
> hotplug with MAC passthrough enabled. After unplug/replug, the interface may appear with an dock MAC address but not MAC passthrough address then cause stale MAC and wired networking does not work.
> Cold boot is unaffected; issue is hotplug-specific.
> 
> Affected systems include Dell platforms with Thunderbolt docks such as
> SD25TB5-class docks carrying Intel I226 ethernet.
> 
> [Fix]
> Increase the existing Thunderbolt MAC passthrough wait in igc probe path:
> - from 600ms
> - to 1000ms
> 
> Ubuntu already carries a SAUCE workaround (commit 534981aaa831) that uses
> fixed delay timing. Newer Dell docks need a longer timing window.
> 
> Debug testing shows BIOS MAC update timing:
> - cold boot: MAC already correct at probe start
> - hotplug: MAC becomes correct at ~300-800ms after probe starts
> 
> Use 1000ms (observed 800ms worst-case + margin) to make hotplug reliable.
> 
> Upstream context:
> https://lore.kernel.org/lkml/20210702045120.22855-2-aaron.ma@canonical.com/
> (Upstream preferred polling over fixed delay; Ubuntu keeps minimal stable
> fixed-delay workaround.)
> 
> [Test Plan]
> 1. Boot with dock attached; confirm interface has valid MAC and link works.
> 2. Unplug dock, wait 5s, replug, wait for enumeration.
> 3. Verify MAC is valid/correct and connectivity works.
> 4. Repeat hotplug cycle 10 times.
> 
> Expected results:
> - Without this change: intermittent hotplug failures (~50-80% observed).
> - With this change: MAC is correct and networking works on every cycle.
> 
> [Where problems could occur]
> - Probe time for Thunderbolt-attached igc devices increases by 400ms.
> - Scope is limited to pci_is_thunderbolt_attached() path.
> - If a future dock requires >1000ms, hotplug failure could still occur.
> - No functional changes beyond extending an existing sleep.
> 
> Max Lee (1):
>   UBUNTU: SAUCE: igc: Increase Thunderbolt MAC passthrough delay to
>     1000ms
> 
>  drivers/net/ethernet/intel/igc/igc_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --
> 2.53.0
> 
> 

Acked-by: Tim Whisonant <tim.whisonant at canonical.com>