From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH v6 net] stmmac: strip all VLAN tag types when kernel
 802.1Q support is selected
Date: Sun, 10 Jun 2018 12:29:18 -0700 (PDT)
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From: Elad Nachman <eladv6@gmail.com>
Date: Fri, 8 Jun 2018 12:19:29 +0300

> stmmac reception handler calls stmmac_rx_vlan() to strip the vlan before 
> calling napi_gro_receive().
> 
> The function assumes VLAN tagged frames are always tagged with 
> 802.1Q protocol, and assigns ETH_P_8021Q to the skb by hard-coding
> the parameter on call to __vlan_hwaccel_put_tag() .
> 
> This causes packets not to be passed to the VLAN slave if it was created 
> with 802.1AD protocol
> (ip link add link eth0 eth0.100 type vlan proto 802.1ad id 100).
> 
> This fix passes the protocol from the VLAN header into 
> __vlan_hwaccel_put_tag() instead of using the hard-coded value of
> ETH_P_8021Q.
> 
> NETIF_F_HW_VLAN_CTAG_RX check was removed and instead the strip action 
> is dependent upon a preprocessor define which is defined when 802.1Q 
> support is selected in the kernel config. 
> 
> NETIF_F_HW_VLAN_STAG_RX feature was added to be in line with the driver 
> actual abilities.
> 
> Signed-off-by: Elad Nachman <eladn@gilat.com>

You can't remove the NETIF_F_* checks.

If the user doesn't have VLAN offloading enabled, the VLAN tags should
be left in the packet as-is.

It can't be controlled by a CPP check.