[PATCH net v2] net: stmmac: hold runtime PM reference in setup_tc

[Lorenzo Bianconi]

The qdisc offload callbacks invoked by stmmac_setup_tc() program
MTL/MAC registers, but they can be reached while the interface is down,
when stmmac_release() has dropped the runtime PM usage counter and the
device may be suspended with its clocks gated. Accessing the registers
in that state can trigger a bus error.

Hold a runtime PM reference while configuring the register-touching
qdisc offloads (mqprio, cbs and taprio) so the device is active, and its
clocks enabled, whenever the MTL/MAC registers are programmed.

The TC block callback stmmac_setup_tc_block_cb() programs the MTL/MAC
registers as well, but it runs asynchronously from stmmac_setup_tc(),
outside the runtime PM reference held there. Hold a runtime PM reference
for the whole stmmac_setup_tc_block_cb() call as well, covering the
cls_u32/cls_flower setup and the queue enable/disable accesses.

No reference is held for the TC_SETUP_BLOCK bookkeeping itself, the
TC_QUERY_CAPS query or the tc-etf path, since none of them touch the
registers synchronously. In particular the block bind/unbind must reach
flow_block_cb_setup_simple() even when the device is suspended, so the
driver never leaves a stale flow_block_cb on its block list.

Fixes: 1f705bc61aee ("net: stmmac: Add support for CBS QDISC")
Fixes: 4dbbe8dde848 ("net: stmmac: Add support for U32 TC filter using Flexible RX Parser")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi at oss.qualcomm.com>
---
Changes in v2:
- Return -EOPNOTSUPP in stmmac_setup_tc_block_cb() for unsupported TC
  blocks.
- Link to v1: https://lore.kernel.org/r/20260824-stmmac-setup-tc-enable-pm-v1-1-45172d241a4b@oss.qualcomm.com
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 35 ++++++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index efa35cfecc4f..90753d5af6d6 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -6393,9 +6393,13 @@ static int stmmac_setup_tc_block_cb(enum tc_setup_type type, void *type_data,
 				    void *cb_priv)
 {
 	struct stmmac_priv *priv = cb_priv;
-	int ret = -EOPNOTSUPP;
+	int ret;
 
 	if (!tc_cls_can_offload_and_chain0(priv->dev, type_data))
+		return -EOPNOTSUPP;
+
+	ret = pm_runtime_resume_and_get(priv->device);
+	if (ret < 0)
 		return ret;
 
 	__stmmac_disable_all_queues(priv);
@@ -6408,10 +6412,13 @@ static int stmmac_setup_tc_block_cb(enum tc_setup_type type, void *type_data,
 		ret = stmmac_tc_setup_cls(priv, priv, type_data);
 		break;
 	default:
+		ret = -EOPNOTSUPP;
 		break;
 	}
 
 	stmmac_enable_all_queues(priv);
+	pm_runtime_put(priv->device);
+
 	return ret;
 }
 
@@ -6421,26 +6428,46 @@ static int stmmac_setup_tc(struct net_device *ndev, enum tc_setup_type type,
 			   void *type_data)
 {
 	struct stmmac_priv *priv = netdev_priv(ndev);
+	int ret;
 
 	switch (type) {
 	case TC_QUERY_CAPS:
 		return stmmac_tc_query_caps(priv, priv, type_data);
 	case TC_SETUP_QDISC_MQPRIO:
-		return stmmac_tc_setup_mqprio(priv, priv, type_data);
+		ret = pm_runtime_resume_and_get(priv->device);
+		if (ret < 0)
+			return ret;
+
+		ret = stmmac_tc_setup_mqprio(priv, priv, type_data);
+		break;
 	case TC_SETUP_BLOCK:
 		return flow_block_cb_setup_simple(type_data,
 						  &stmmac_block_cb_list,
 						  stmmac_setup_tc_block_cb,
 						  priv, priv, true);
 	case TC_SETUP_QDISC_CBS:
-		return stmmac_tc_setup_cbs(priv, priv, type_data);
+		ret = pm_runtime_resume_and_get(priv->device);
+		if (ret < 0)
+			return ret;
+
+		ret = stmmac_tc_setup_cbs(priv, priv, type_data);
+		break;
 	case TC_SETUP_QDISC_TAPRIO:
-		return stmmac_tc_setup_taprio(priv, priv, type_data);
+		ret = pm_runtime_resume_and_get(priv->device);
+		if (ret < 0)
+			return ret;
+
+		ret = stmmac_tc_setup_taprio(priv, priv, type_data);
+		break;
 	case TC_SETUP_QDISC_ETF:
 		return stmmac_tc_setup_etf(priv, priv, type_data);
 	default:
 		return -EOPNOTSUPP;
 	}
+
+	pm_runtime_put(priv->device);
+
+	return ret;
 }
 
 static u16 stmmac_select_queue(struct net_device *dev, struct sk_buff *skb,

---
base-commit: f967455fb2a5a2079b9eb5823e9ccf359174bf9f
change-id: 20260824-stmmac-setup-tc-enable-pm-149aa563d797

Best regards,
-- 
Lorenzo Bianconi <lorenzo.bianconi at oss.qualcomm.com>