[PATCH net v2 2/6] net: stmmac: Enable double VLAN processing only when supported

stmmac_vlan_update() turns on double/S-VLAN processing whenever an
802.1ad VLAN is registered, without checking whether the MAC actually
supports double VLAN processing. That capability is reported in
dma_cap.dvlan.

This was found while investigating a separate bug in the double VLAN RX
stripping path. The outer 802.1ad tags were unexpectedly stripped by the
MAC (because the ESVL bit was set).

Check dma_cap.dvlan before enabling EDVLP/ESVL/DOVLTC bits, so that double
VLAN processing is enabled only on supported hardware. Also, advertise
NETIF_F_HW_VLAN_STAG_RX and NETIF_F_HW_VLAN_STAG_FILTER only when
dma_cap.dvlan is set.

Fixes: 3cd1cfcba26e ("net: stmmac: Implement VLAN Hash Filtering in XGMAC")
Signed-off-by: Ovidiu Panait <[email protected]>
---
v2 changes:
- Advertised NETIF_F_HW_VLAN_STAG_RX and NETIF_F_HW_VLAN_STAG_FILTER only
  when dma_cap.dvlan is set (reported by Sashiko).

 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 16fe56a1f617..880cf3fab913 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -6820,6 +6820,9 @@ static int stmmac_vlan_update(struct stmmac_priv *priv, bool is_double)
 	if (!netif_running(priv->dev))
 		return 0;
 
+	if (!priv->dma_cap.dvlan)
+		is_double = false;
+
 	return stmmac_update_vlan_hash(priv, priv->hw, hash, is_double);
 }
 
@@ -7954,14 +7957,18 @@ static int __stmmac_dvr_probe(struct device *device,
 	ndev->watchdog_timeo = msecs_to_jiffies(watchdog);
 #ifdef STMMAC_VLAN_TAG_USED
 	/* Both mac100 and gmac support receive VLAN tag detection */
-	ndev->features |= NETIF_F_HW_VLAN_CTAG_RX | NETIF_F_HW_VLAN_STAG_RX;
+	ndev->features |= NETIF_F_HW_VLAN_CTAG_RX;
+	if (priv->dma_cap.dvlan)
+		ndev->features |= NETIF_F_HW_VLAN_STAG_RX;
+
 	if (dwmac_is_xmac(priv->plat->core_type)) {
 		ndev->hw_features |= NETIF_F_HW_VLAN_CTAG_RX;
 		priv->hw->hw_vlan_en = true;
 	}
 	if (priv->dma_cap.vlhash) {
 		ndev->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
-		ndev->features |= NETIF_F_HW_VLAN_STAG_FILTER;
+		if (priv->dma_cap.dvlan)
+			ndev->features |= NETIF_F_HW_VLAN_STAG_FILTER;
 	}
 	if (priv->dma_cap.vlins)
 		ndev->features |= NETIF_F_HW_VLAN_CTAG_TX;
-- 
2.34.1