net: stmmac: propagate FPE preemption-class mapping errors

stmmac_fpe_map_preemption_class() dispatches through the
stmmac_do_void_callback() helper, which forces the callback's return
value to 0 whenever the op pointer is populated. As a result the
-EINVAL returned by dwmac5_fpe_map_preemption_class() (e.g. when a
preemptible TC owns more than one TXQ under SP scheduling) is silently
swallowed by every caller.

Switch the dispatch macro to stmmac_do_callback() so the callback's real
result is propagated, and honour it in the taprio and mqprio qdisc
offload.

Note that the taprio "if (ret)" check in tc_taprio_configure() used to
be dead code and now becomes live: a preemptible TC spanning more than
one TXQ under SP scheduling cannot be programmed in hardware, so a
taprio or mqprio configuration that previously returned success while
leaving the preemption-class register unprogrammed now fails with
-EINVAL. For taprio, the failure also runs the disable path, tearing
down the schedule that was just installed; this is the intended
behaviour.

Fixes: 195e4f409a40 ("net: stmmac: support fp parameter of tc-mqprio")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>
Link: https://patch.msgid.link/20260911-stmmac-tc_setup_dwmac510_mqprio-error-path-v3-1-a76b1e2547c1@oss.qualcomm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 10 insertions, 11 deletions

diff --git a/drivers/net/ethernet/stmicro/stmmac/hwif.h b/drivers/net/ethernet/stmicro/stmmac/hwif.h
index 04dafec021b4..9314bcb85c22 100644
--- a/drivers/net/ethernet/stmicro/stmmac/hwif.h
+++ b/drivers/net/ethernet/stmicro/stmmac/hwif.h
@@ -494,7 +494,7 @@ struct stmmac_ops {
 #define stmmac_set_arp_offload(__priv, __args...) \
 	stmmac_do_void_callback(__priv, mac, set_arp_offload, __args)
 #define stmmac_fpe_map_preemption_class(__priv, __args...) \
-	stmmac_do_void_callback(__priv, mac, fpe_map_preemption_class, __args)
+	stmmac_do_callback(__priv, mac, fpe_map_preemption_class, __args)
 
 /* PTP and HW Timer helpers */
 struct stmmac_hwtimestamp {
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
index 14cabe76e53e..5398616fcdfe 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
@@ -970,7 +970,7 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
 	struct netlink_ext_ack *extack = qopt->mqprio.extack;
 	struct timespec64 time, current_time, qopt_time;
 	ktime_t current_time_ns;
-	int i, ret = 0;
+	int err, i, ret = 0;
 	u64 ctr;
 
 	if (qopt->base_time < 0)
@@ -1120,9 +1120,9 @@ disable:
 		mutex_unlock(&priv->est_lock);
 	}
 
-	stmmac_fpe_map_preemption_class(priv, priv->dev, extack, 0);
+	err = stmmac_fpe_map_preemption_class(priv, priv->dev, extack, 0);
 
-	return ret;
+	return qopt->cmd == TAPRIO_CMD_DESTROY ? err : ret;
 }
 
 static void tc_taprio_stats(struct stmmac_priv *priv,
@@ -1237,14 +1237,15 @@ static int tc_query_caps(struct stmmac_priv *priv,
 	}
 }
 
-static void stmmac_reset_tc_mqprio(struct net_device *ndev,
-				   struct netlink_ext_ack *extack)
+static int stmmac_reset_tc_mqprio(struct net_device *ndev,
+				  struct netlink_ext_ack *extack)
 {
 	struct stmmac_priv *priv = netdev_priv(ndev);
 
 	netdev_reset_tc(ndev);
 	netif_set_real_num_tx_queues(ndev, priv->plat->tx_queues_to_use);
-	stmmac_fpe_map_preemption_class(priv, ndev, extack, 0);
+
+	return stmmac_fpe_map_preemption_class(priv, ndev, extack, 0);
 }
 
 static int tc_setup_dwmac510_mqprio(struct stmmac_priv *priv,
@@ -1257,10 +1258,8 @@ static int tc_setup_dwmac510_mqprio(struct stmmac_priv *priv,
 	u32 num_tc = qopt->num_tc;
 	int err;
 
-	if (!num_tc) {
-		stmmac_reset_tc_mqprio(ndev, extack);
-		return 0;
-	}
+	if (!num_tc)
+		return stmmac_reset_tc_mqprio(ndev, extack);
 
 	err = netdev_set_num_tc(ndev, num_tc);
 	if (err)