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

On 2026-09-24, Matt Vollrath wrote:

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.

Thanks Matt,
I've tested this approach on two I219-LM boxes, each attached to a different switch:
one a TP-Link TL-SG108PE V3, and the other a Cisco Catalyst 9200.

On the Cisco with jumbo frames, I'm seeing, via a diagnostic message, that
the fix appears to fire and work. I have also noticed that I no longer see
it on every boot, but this may be correct as I've not seen traffic stalls.

With 1500 mtu, I'm seeing it engage fairly regularly with the TP-Link but
not the Cisco. I'm guessing it is related to how the Cisco negotiates. In both cases
traffic doesn't seem to stall.

I think you are correct about flow control being a red herring since
both switches advertise no pause (Flow Control: None) before and after
recovery.

I'd like to drop my patch in favour of your fix.

How should I proceed, should I propose a patch with suggested-by you, or with your authorship and
tested by me?

For completeness, here is the diff I tested (I added an e_info so I could see it fire on the
test rig; happy to drop that line - it isn't needed for the fix):

--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c

@@ -5254,9 +5254,16 @@
 					usleep_range(10000, 20000);
 					pcim_state = er32(STATUS);
 
-					/* Checking if MAC exited DMoff state */
-					if (!(pcim_state & E1000_STATUS_PCIM_STATE))
-						e1000_phy_hw_reset(&adapter->hw);
+					/* Checking if MAC exited DMoff state.  A bare
+					 * PHY reset here does not re-run the jumbo
+					 * workaround (e1000_lv_jumbo_workaround_ich8lan),
+					 * so request a full reset instead, which does.
+					 */
+					if (!(pcim_state & E1000_STATUS_PCIM_STATE)) {
+						e_info("full reset on DMoff exit to restore jumbo-frame configuration\n");
+						adapter->flags |= FLAG_RESTART_NOW;
+						goto link_up;
+					}
 				}
 			}