igc: recalculate Qbv end_time by considering cycle time

Qbv users can specify a cycle time that is not equal to the total GCL
intervals. Hence, recalculation is necessary here to exclude the time
interval that exceeds the cycle time. As those GCL which exceeds the
cycle time will be truncated.

According to IEEE Std. 802.1Q-2018 section 8.6.9.2, once the end of
the list is reached, it will switch to the END_OF_CYCLE state and
leave the gates in the same state until the next cycle is started.

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

@@ -6067,6 +6067,21 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 
 		end_time += e->interval;
 
+		/* If any of the conditions below are true, we need to manually
+		 * control the end time of the cycle.
+		 * 1. Qbv users can specify a cycle time that is not equal
+		 * to the total GCL intervals. Hence, recalculation is
+		 * necessary here to exclude the time interval that
+		 * exceeds the cycle time.
+		 * 2. According to IEEE Std. 802.1Q-2018 section 8.6.9.2,
+		 * once the end of the list is reached, it will switch
+		 * to the END_OF_CYCLE state and leave the gates in the
+		 * same state until the next cycle is started.
+		 */
+		if (end_time > adapter->cycle_time ||
+		    n + 1 == qopt->num_entries)
+			end_time = adapter->cycle_time;
+
 		for (i = 0; i < adapter->num_tx_queues; i++) {
 			struct igc_ring *ring = adapter->tx_ring[i];