netdev - [PATCH iwl-next] igc: Restore default Qbv schedule when changing channels

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Message-Id: <20251107-igc_mqprio_channels-v1-1-42415562d0f8@linutronix.de>
Date: Fri, 07 Nov 2025 14:31:36 +0100
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Tony Nguyen <anthony.l.nguyen@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Vinicius Costa Gomes <vinicius.gomes@...el.com>, 
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, 
 Kurt Kanzenbach <kurt@...utronix.de>
Subject: [PATCH iwl-next] igc: Restore default Qbv schedule when changing
 channels

The MQPRIO (and ETF) offload utilizes the TSN Tx mode. This mode is always
coupled to Qbv. Therefore, the driver sets a default Qbv schedule of all gates
opened and a cycle time of 1s. This schedule is set during probe.

However, the following sequence of events lead to Tx issues:

 - Boot a dual core system
   probe():
     igc_tsn_clear_schedule():
       -> Default Schedule is set
       Note: At this point the driver has allocated two Tx/Rx queues, because
       there are only two CPU(s).

 - ethtool -L enp3s0 combined 4
   igc_ethtool_set_channels():
     igc_reinit_queues()
       -> Default schedule is gone, per Tx ring start and end time are zero

  - tc qdisc replace dev enp3s0 handle 100 parent root mqprio \
      num_tc 4 map 3 3 2 2 0 1 1 1 3 3 3 3 3 3 3 3 \
      queues 1@0 1@1 1@2 1@3 hw 1
    igc_tsn_offload_apply():
      igc_tsn_enable_offload():
        -> Writes zeros to IGC_STQT(i) and IGC_ENDQT(i) -> Boom

Therefore, restore the default Qbv schedule after changing the amount of
channels.

Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 728d7ca5338bf27c3ce50a2a497b238c38cfa338..e4200fcb2682ccd5b57abb0d2b8e4eb30df117df 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -7761,6 +7761,8 @@ int igc_reinit_queues(struct igc_adapter *adapter)
 	if (netif_running(netdev))
 		err = igc_open(netdev);

+	igc_tsn_clear_schedule(adapter);
+
 	return err;
 }

---
base-commit: 6fc33710cd6c55397e606eeb544bdf56ee87aae5
change-id: 20251107-igc_mqprio_channels-2329166e898b

Best regards,
-- 
Kurt Kanzenbach <kurt@...utronix.de>