Re: [PATCH net v6 5/5] net: stmmac: Disable S-Tag processing on dwmac4
flat view
From: Maxime Chevallier <maxime.chevallier@bootlin.com>
Date: 2026-09-30 21:51:32
Also in:
linux-arm-kernel, lkml
Hi, On 9/28/26 22:34, Ovidiu Panait wrote:
Currently, hardware VLAN stripping is broken for 802.1ad tags. vlan_rx_hw()
hardcodes ETH_P_8021Q when putting the hardware tag into the skb, rather
than using the actual protocol from the packet. Because of this, packets
that contain a 802.1ad outer tag are incorrectly passed up the stack as
having an 802.1Q tag. This causes QinQ ping between two hosts to fail.
vlan_rx_hw() is shared by dwxgmac2 and dwmac4: on dwxgmac2 the tag type
is available in the RDES3 write-back descriptor (the ET_LT field), so the
outer tag type can be determined based on that info. However, dwmac4
doesn't seem to provide the tag type. The Length/Type field in RDES3 only
indicates whether the packet is single or double-tagged, not which tag
type was stripped.
Since dwmac4 cannot report the stripped tag type, it cannot support
hardware S-Tag stripping correctly. Therefore, restrict the
NETIF_F_HW_VLAN_STAG_RX and NETIF_F_HW_VLAN_STAG_FILTER advertisement
to dwxgmac2 only.
With this, 802.1ad tags are left in place and handled by the software
VLAN path.
Fixes: 750011e239a5 ("net: stmmac: Add support for HW-accelerated VLAN stripping")
Signed-off-by: Ovidiu Panait <redacted>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>I ran your proposed QinQ selftests on stm32mp157a (dwmac4), and it correctly fixes the problem on that core. Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com> Maxime
quoted hunk ↗ jump to hunk
--- v6 changes: None. v5 changes: - Rebased on top of latest changes. - Added Reviewed-by tag from Maxime. v4 changes: - Dropped all "double VLAN" references from the commit title/message. - Rebased on top of the S-VLAN rework. drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index b007ff120471..5af245fd9ba0 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c@@ -6211,7 +6211,7 @@ static netdev_features_t stmmac_fix_features(struct net_device *dev, if (priv->plat->bugged_jumbo && (dev->mtu > ETH_DATA_LEN)) features &= ~NETIF_F_CSUM_MASK; - if (dwmac_is_xmac(priv->plat->core_type)) { + if (priv->plat->core_type == DWMAC_CORE_XGMAC) { if (features & NETIF_F_HW_VLAN_CTAG_RX) features |= NETIF_F_HW_VLAN_STAG_RX; else@@ -7990,14 +7990,18 @@ 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->plat->core_type == DWMAC_CORE_XGMAC) + 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->plat->core_type == DWMAC_CORE_XGMAC) + ndev->features |= NETIF_F_HW_VLAN_STAG_FILTER; } if (priv->dma_cap.vlins) ndev->features |= NETIF_F_HW_VLAN_CTAG_TX;