igc: assign highest TX queue number as highest priority in mqprio

Previously, TX arbitration prioritized queues based on the TC they were
mapped to. A queue mapped to TC 3 had higher priority than one mapped to
TC 0.

To improve code reuse for upcoming patches and align with typical NIC
behavior, this patch updates the logic to prioritize higher queue numbers
when mqprio is used. As a result, queue 0 becomes the lowest priority and
queue 3 becomes the highest.

This patch also introduces igc_tsn_is_tc_to_queue_priority_ordered() to
preserve the original TC-based priority rule and reject configurations
where a higher TC maps to a lower queue offset.

Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: Faizal Rahim <[email protected]>
Tested-by: Mor Bar-Gabay <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index f3a312c9413b..1322a2db6dba 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -6724,6 +6724,20 @@ static void igc_save_mqprio_params(struct igc_adapter *adapter, u8 num_tc,
 		adapter->queue_per_tc[i] = offset[i];
 }
 
+static bool
+igc_tsn_is_tc_to_queue_priority_ordered(struct tc_mqprio_qopt_offload *mqprio)
+{
+	int num_tc = mqprio->qopt.num_tc;
+	int i;
+
+	for (i = 1; i < num_tc; i++) {
+		if (mqprio->qopt.offset[i - 1] > mqprio->qopt.offset[i])
+			return false;
+	}
+
+	return true;
+}
+
 static int igc_tsn_enable_mqprio(struct igc_adapter *adapter,
 				 struct tc_mqprio_qopt_offload *mqprio)
 {
@@ -6756,6 +6770,12 @@ static int igc_tsn_enable_mqprio(struct igc_adapter *adapter,
 		}
 	}
 
+	if (!igc_tsn_is_tc_to_queue_priority_ordered(mqprio)) {
+		NL_SET_ERR_MSG_MOD(mqprio->extack,
+				   "tc to queue mapping must preserve increasing priority (higher tc -> higher queue)");
+		return -EOPNOTSUPP;
+	}
+
 	/* Preemption is not supported yet. */
 	if (mqprio->preemptible_tcs) {
 		NL_SET_ERR_MSG_MOD(mqprio->extack,