Re: [PATCH net-next v2] net: libwx: disable TX VLAN offload for packets with >2 VLAN tags

[Jacob Keller <jacob.e.keller@intel.com>]

On 7/12/2026 11:04 PM, 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>


Is there a reason this was targeted at net-next instead of as a bug fix
to net with a Fixes tag to the commit which first introduced VLAN tagging?

Thanks,
Jake

> ---
> v2:
> - Remove redundant 'parse_depth'.
> - Optimize the loop.
> 
> v1: https://lore.kernel.org/all/C1BF77C0E073A40C+20260710071831.210196-1-jiawenwu@trustnetic.com
> ---
>  drivers/net/ethernet/wangxun/libwx/wx_lib.c | 24 +++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/net/ethernet/wangxun/libwx/wx_lib.c b/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> index 814d88d2aee4..34542b3dc884 100644
> --- a/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> +++ b/drivers/net/ethernet/wangxun/libwx/wx_lib.c
> @@ -3228,6 +3228,30 @@ netdev_features_t wx_features_check(struct sk_buff *skb,
>  				    netdev_features_t features)
>  {
>  	struct wx *wx = netdev_priv(netdev);
> +	__be16 type = skb->protocol;
> +	u16 vlan_depth = ETH_HLEN;
> +	u32 vlan_num = 0;
> +
> +	if (skb_vlan_tag_present(skb))
> +		vlan_num++;
> +
> +	while (eth_type_vlan(type)) {
> +		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++;
> +
> +		if (vlan_num > 2) {
> +			features &= ~(NETIF_F_HW_VLAN_CTAG_TX |
> +				      NETIF_F_HW_VLAN_STAG_TX);
> +			break;
> +		}
> +	}
>  
>  	if (!skb->encapsulation)
>  		return features;