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

[AceLan Kao]

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(-)

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2.53.0