Re: [PATCH net-next] net: libwx: disable TX VLAN offload for packets with >2 VLAN tags

[Przemek Kitszel <przemyslaw.kitszel@intel.com>]

On 7/10/26 09:18, Jiawen Wu wrote:
> The current hardware does not support TX VLAN offload for packets with
> three or more VLAN tags. When such packets are transmitted with hardware
> VLAN offload enabled, the hardware may malfunction or produce corrupted
> frames.
> 
> Add a check in wx_features_check() to parse the VLAN depth of the
> skb. If more than two VLAN tags are detected (including both the
> hardware tag and in-band tags), strip NETIF_F_HW_VLAN_CTAG_TX and
> NETIF_F_HW_VLAN_STAG_TX from the feature set. This forces the
> kernel networking stack to handle VLAN insertion in software for
> these specific packets, ensuring correct transmission.
> 
> Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
> ---
>   drivers/net/ethernet/wangxun/libwx/wx_lib.c | 25 +++++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/net/ethernet/wangxun/libwx/wx_lib.c b/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> index 814d88d2aee4..65dab6bd8a39 100644
> --- a/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> +++ b/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> @@ -3223,12 +3223,37 @@ netdev_features_t wx_fix_features(struct net_device *netdev,
>   EXPORT_SYMBOL(wx_fix_features);
>   
>   #define WX_MAX_TUNNEL_HDR_LEN	80
> +#define WX_VLAN_MAX_DEPTH	8
>   netdev_features_t wx_features_check(struct sk_buff *skb,
>   				    struct net_device *netdev,
>   				    netdev_features_t features)
>   {
>   	struct wx *wx = netdev_priv(netdev);
> +	u16 parse_depth = WX_VLAN_MAX_DEPTH;
> +	__be16 type = skb->protocol;
> +	u16 vlan_depth = ETH_HLEN;
> +	u32 vlan_num = 0;
>   
> +	if (!skb_vlan_tag_present(skb))

this if jumping over the loop with essentially the same condition
does not help much, I would just remove

> +		goto tunnel_check;
> +
> +	vlan_num++;
> +	while (eth_type_vlan(type) && --parse_depth) {
> +		struct vlan_hdr vhdr, *vh;
> +
> +		vh = skb_header_pointer(skb, vlan_depth, sizeof(vhdr), &vhdr);
> +		if (unlikely(!vh))
> +			break;
> +
> +		type = vh->h_vlan_encapsulated_proto;
> +		vlan_depth += VLAN_HLEN;
> +		vlan_num++;

parse depth of 8 does not make sense if you are detecting
"are the three first protocols a VLAN"

> +	}
> +
> +	if (vlan_num > 2)
> +		features &= ~(NETIF_F_HW_VLAN_CTAG_TX |
> +			      NETIF_F_HW_VLAN_STAG_TX);

you could move this if condition inside a loop with an added "break"

> +tunnel_check:
>   	if (!skb->encapsulation)
>   		return features;
>