Re: [PATCH net 0/5] net: stmmac: Fix double VLAN 802.1ad tag handling

[Maxime Chevallier]

Hi Ovidiu,

On 7/29/26 11:51, 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 an 802.1ad outer tag are incorrectly passed up the stack as
> having an 802.1Q tag.
> 
> This issue was observed on the Renesas RZ/V2H platform (which has a dwmac4
> IP), when testing QinQ ping:
> 
>   # DUT
>   ip link add link end0 name end0.100 type vlan proto 802.1ad id 100
>   ip link add link end0.100 name end0.100.200 type vlan proto 802.1q id 200
>   ip addr add 172.16.3.2/24 dev end0.100.200
>   ip link set end0 up
>   ip link set end0.100 up
>   ip link set end0.100.200 up
> 
>   # Peer
>   ip link add link eth0 name eth0.100 type vlan proto 802.1ad id 100
>   ip link add link eth0.100 name eth0.100.200 type vlan proto 802.1q id 200
>   ip addr add 172.16.3.1/24 dev eth0.100.200
>   ip link set eth0 up
>   ip link set eth0.100 up
>   ip link set eth0.100.200 up
>   ping 172.16.3.2
>     -- FAIL --
> 
> This series addresses the issue for both dwmac4 and dwxgmac2:
> - dwmac4: since dwmac4 does not expose the tag type in the RDES3
>   descriptor, it cannot support hardware double VLAN stripping correctly.
>   This series disables double VLAN stripping for it, so the 802.1ad tags
>   are left in place and are handled by the software VLAN path.
> 
> - dwxgmac2: the RDES3 descriptor does report the type, so the code was
>   updated to read it instead of hardcoding ETH_P_8021Q.
> 
> Note: patch 5/5 was compile tested only, as I do not have the hardware.
> However, it uses the same codepath as dwmac4, so it has the same issue.

I was able to reproduce the issue on imx8mp, and indeed this series fixes it.

I'll try to do a more thorough review soon, but this is a good finding, thanks
for fixing that :)

Maxime