Re: [PATCH net v6 5/5] net: stmmac: Disable S-Tag processing on dwmac4

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

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 <ovidiu.panait.rb@renesas.com>
> 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

> ---
> 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;