[PATCH net 2/5] net: stmmac: Enable double VLAN processing only when supported

[Ovidiu Panait]

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.

Fixes: 3cd1cfcba26e ("net: stmmac: Implement VLAN Hash Filtering in XGMAC")
Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@xxxxxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index fc9f1342ea45..ecb8eb7e29ab 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -6802,6 +6802,9 @@ 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);
 }
 
-- 
2.34.1