[PATCH 6.18 024/227] igc: Restore default Qbv schedule when changing channels

Greg Kroah-Hartman
2026-01-28T15:51:29Z

From: Kurt Kanzenbach <kurt@linutronix.de>

[ Upstream commit 41a9a6826f20a524242a6c984845c4855f629841 ]

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@linutronix.de>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 bb783042d1af9..4b39329e9e32b 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 728d7ca5338bf..21e67e7534562 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;
}

--
2.51.0