[PATCH net v2 2/5] net: mvneta: fix the removal of the mqprio offload

[Josef Schlehofer <pepe.schlehofer@gmail.com>]

Deleting an offloaded mqprio qdisc leaves its traffic classes and
per-queue rate limits in place.

mqprio_disable_offload() passes an all-zero configuration, so qopt.hw
is 0 and mvneta_setup_mqprio() returns before it reaches the teardown
code.

Check qopt.hw only when traffic classes are set up.

A replacement qdisc is set up before the old one is torn down.
Replacing an offloaded mqprio qdisc with another mqprio under a new
handle therefore loses the new configuration, as with software mqprio.

Tested on a Turris Omnia (Armada 385) with 10 Mbit/s limits on a
100 Mbit/s link. After the qdisc was deleted, only TX queues 0-3 were
used and the link carried 19 Mbit/s. With this patch and the previous
one, the queues above 3 are used again and the link reaches 94 Mbit/s.

Fixes: e7ca75fe6662 ("net: mvneta: Don't force-set the offloading flag")
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 9b9efac2846e..79711a117c39 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -5251,11 +5251,12 @@ static int mvneta_setup_mqprio(struct net_device *dev,
 	int rxq, txq, tc, ret;
 	u8 num_tc;
 
-	if (mqprio->qopt.hw != TC_MQPRIO_HW_OFFLOAD_TCS)
-		return 0;
-
 	num_tc = mqprio->qopt.num_tc;
 
+	/* On removal the qdisc passes an all-zero qopt, with hw 0 */
+	if (num_tc && mqprio->qopt.hw != TC_MQPRIO_HW_OFFLOAD_TCS)
+		return 0;
+
 	if (num_tc > rxq_number)
 		return -EINVAL;
 
-- 
2.54.0 (Apple Git-157)