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

["Jiawen Wu" <jiawenwu@trustnetic.com>]

On Wed, Jul 15, 2026 8:27 AM, Jacob Keller wrote:
> 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

Probably because I couldn't find a Fixes tag for it...

> 
> > ---
> > 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;
> 
>