igc: Set Qbv start_time and end_time to end_time if not being configured in GCL

The default setting of end_time minus start_time is whole 1 second.
Thus, if it's not being configured in any GCL entry then it will be
staying at original 1 second.

This patch is changing the start_time and end_time to be end_time as
if setting zero will be having weird HW behavior where the gate will
not be fully closed.

Fixes: ec50a9d4 ("igc: Add support for taprio offloading")
Signed-off-by: Tan Tee Min <tee.min.tan@linux.intel.com>
Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_main.c

@@ -6043,6 +6043,7 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 	bool queue_configured[IGC_MAX_TX_QUEUES] = { };
 	u32 start_time = 0, end_time = 0;
 	size_t n;
+	int i;
 
 	adapter->qbv_enable = qopt->enable;
 
@@ -6063,7 +6064,6 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 
 	for (n = 0; n < qopt->num_entries; n++) {
 		struct tc_taprio_sched_entry *e = &qopt->entries[n];
-		int i;
 
 		end_time += e->interval;
 
@@ -6102,6 +6102,18 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 		start_time += e->interval;
 	}
 
+	/* Check whether a queue gets configured.
+	 * If not, set the start and end time to be end time.
+	 */
+	for (i = 0; i < adapter->num_tx_queues; i++) {
+		if (!queue_configured[i]) {
+			struct igc_ring *ring = adapter->tx_ring[i];
+
+			ring->start_time = end_time;
+			ring->end_time = end_time;
+		}
+	}
+
 	return 0;
 }