[PATCH net 5/5] igc: fix the validation logic for taprio's gate list

[Tony Nguyen <anthony.l.nguyen@intel.com>]

From: AKASHI Takahiro <takahiro.akashi@linaro.org>

The check introduced in the commit a5fd39464a40 ("igc: Lift TAPRIO schedule
restriction") can detect a false positive error in some corner case.
For instance,
    tc qdisc replace ... taprio num_tc 4
	...
	sched-entry S 0x01 100000	# slot#1
	sched-entry S 0x03 100000	# slot#2
	sched-entry S 0x04 100000	# slot#3
	sched-entry S 0x08 200000	# slot#4
	flags 0x02			# hardware offload

Here the queue#0 (the first queue) is on at the slot#1 and #2,
and off at the slot#3 and #4. Under the current logic, when the slot#4
is examined, validate_schedule() returns *false* since the enablement
count for the queue#0 is two and it is already off at the previous slot
(i.e. #3). But this definition is truely correct.

Let's fix the logic to enforce a strict validation for consecutively-opened
slots.

Fixes: a5fd39464a40 ("igc: Lift TAPRIO schedule restriction")
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
Acked-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 | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 2928a6c73692..25fc6c65209b 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -6010,18 +6010,18 @@ static bool validate_schedule(struct igc_adapter *adapter,
 		if (e->command != TC_TAPRIO_CMD_SET_GATES)
 			return false;
 
-		for (i = 0; i < adapter->num_tx_queues; i++) {
-			if (e->gate_mask & BIT(i))
+		for (i = 0; i < adapter->num_tx_queues; i++)
+			if (e->gate_mask & BIT(i)) {
 				queue_uses[i]++;
 
-			/* 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;
-		}
+				/* 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;
+			}
 	}
 
 	return true;
-- 
2.38.1