igc: Lift TAPRIO schedule restriction

Add support for Qbv schedules where one queue stays open
in consecutive entries. Currently that's not supported.

Example schedule:

|tc qdisc replace dev ${INTERFACE} handle 100 parent root taprio num_tc 3 \
|   map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
|   queues 1@0 1@1 2@2 \
|   base-time ${BASETIME} \
|   sched-entry S 0x01 300000 \ # Stream High/Low
|   sched-entry S 0x06 500000 \ # Management and Best Effort
|   sched-entry S 0x04 200000 \ # Best Effort
|   flags 0x02

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Vinicius Costa Gomes <vinicius.gomes@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

@@ -5813,9 +5813,10 @@ static bool validate_schedule(struct igc_adapter *adapter,
 		return false;
 
 	for (n = 0; n < qopt->num_entries; n++) {
-		const struct tc_taprio_sched_entry *e;
+		const struct tc_taprio_sched_entry *e, *prev;
 		int i;
 
+		prev = n ? &qopt->entries[n - 1] : NULL;
 		e = &qopt->entries[n];
 
 		/* i225 only supports "global" frame preemption
@@ -5828,7 +5829,12 @@ static bool validate_schedule(struct igc_adapter *adapter,
 			if (e->gate_mask & BIT(i))
 				queue_uses[i]++;
 
-			if (queue_uses[i] > 1)
+			/* There are limitations: A single queue cannot be
+			 * opened and closed multiple times per cycle unless the
+			 * gate stays open. Check for it.
+			 */
+			if (queue_uses[i] > 1 &&
+			    !(prev->gate_mask & BIT(i)))
 				return false;
 		}
 	}
@@ -5872,6 +5878,7 @@ static int igc_tsn_clear_schedule(struct igc_adapter *adapter)
 static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 				 struct tc_taprio_qopt_offload *qopt)
 {
+	bool queue_configured[IGC_MAX_TX_QUEUES] = { };
 	u32 start_time = 0, end_time = 0;
 	size_t n;
 
@@ -5887,9 +5894,6 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 	adapter->cycle_time = qopt->cycle_time;
 	adapter->base_time = qopt->base_time;
 
-	/* FIXME: be a little smarter about cases when the gate for a
-	 * queue stays open for more than one entry.
-	 */
 	for (n = 0; n < qopt->num_entries; n++) {
 		struct tc_taprio_sched_entry *e = &qopt->entries[n];
 		int i;
@@ -5902,8 +5906,15 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
 			if (!(e->gate_mask & BIT(i)))
 				continue;
 
-			ring->start_time = start_time;
+			/* Check whether a queue stays open for more than one
+			 * entry. If so, keep the start and advance the end
+			 * time.
+			 */
+			if (!queue_configured[i])
+				ring->start_time = start_time;
 			ring->end_time = end_time;
+
+			queue_configured[i] = true;
 		}
 
 		start_time += e->interval;