netdev - [PATCH iwl-net v3] igc: Restore default Qbv schedule when changing channels

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Message-Id: <20251120-igc_mqprio_channels-v3-1-ce7d6f00720d@linutronix.de>
Date: Thu, 20 Nov 2025 09:18:29 +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>, 
 "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>, 
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, 
 Kurt Kanzenbach <kurt@...utronix.de>
Subject: [PATCH iwl-net v3] igc: Restore default Qbv schedule when changing
 channels

The Multi-queue Priority (MQPRIO) and Earliest TxTime First (ETF) offloads
utilize the Time Sensitive Networking (TSN) Tx mode. This mode is always
coupled to IEEE 802.1Qbv time aware shaper (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
   igc_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 CPUs.

 - 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), causing Tx to stall/fail

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

Furthermore, add a restriction to not allow queue reconfiguration when
TSN/Qbv is enabled, because it may lead to inconsistent states.

Fixes: c814a2d2d48f ("igc: Use default cycle 'start' and 'end' values for queues")
Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
---
Changes in v3:
- Adjust commit message and comments (Aleksandr)
- Link to v2: https://lore.kernel.org/r/20251118-igc_mqprio_channels-v2-1-c32563dede2f@linutronix.de

Changes in v2:
- Explain abbreviations (Aleksandr)
- Only clear schedule if no error happened (Aleksandr)
- Add restriction to avoid inconsistent states (Vinicius)
- Target net tree (Vinicius)
- Link to v1: https://lore.kernel.org/r/20251107-igc_mqprio_channels-v1-1-42415562d0f8@linutronix.de
---
 drivers/net/ethernet/intel/igc/igc_ethtool.c | 4 ++--
 drivers/net/ethernet/intel/igc/igc_main.c    | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
index bb783042d1af9c86f18fc033fa4c3e75abb0efe8..4b39329e9e32bf34cef66e69b59d05b54cfeabff 100644
--- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
+++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
@@ -1561,8 +1561,8 @@ static int igc_ethtool_set_channels(struct net_device *netdev,
 	if (ch->other_count != NON_Q_VECTORS)
 		return -EINVAL;

-	/* Do not allow channel reconfiguration when mqprio is enabled */
-	if (adapter->strict_priority_enable)
+	/* Do not allow channel reconfiguration when any TSN qdisc is enabled */
+	if (adapter->flags & IGC_FLAG_TSN_ANY_ENABLED)
 		return -EINVAL;

 	/* Verify the number of channels doesn't exceed hw limits */
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 728d7ca5338bf27c3ce50a2a497b238c38cfa338..21e67e7534562ccfa7bad8769bbafc866ecbc85f 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -7761,6 +7761,11 @@ int igc_reinit_queues(struct igc_adapter *adapter)
 	if (netif_running(netdev))
 		err = igc_open(netdev);

+	if (!err) {
+		/* Restore default IEEE 802.1Qbv schedule after queue reinit */
+		igc_tsn_clear_schedule(adapter);
+	}
+
 	return err;
 }

---
base-commit: bc41fbbf6faa9ffeaf0148019ed631077f7f150f
change-id: 20251107-igc_mqprio_channels-2329166e898b

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