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

[Nazle Asmade, Muhammad Nazim Amirul]

On 30/7/2026 9:57 pm, Ovidiu Panait wrote:
> Hi Nazim Amirul,
> 
>> On 29/7/2026 7:35 pm, Maxime Chevallier wrote:
>>> + Nazim Amirul
>>>
>>> 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.
>>> Nazim Amirul, as you seem to have access to some AgileX5 with XGMAC, can
>> you
>>> see if you can reproduce the issue on your side and if this series
>> solves it ?
>>
>> Hi Maxime,
>>
>> Tested on my end and seeing the same failure as above without this
>> series, is this patch 5 is the only patch needed to fix the problem?
> 
> For dwxgmac2 yes, patch 5 is the only one that is needed. Dwmac4 doesn't report
> the type of the stripped tag (802.1ad vs 802.1Q) so the other patches are needed
> to disable the double VLAN stripping.
> 
> Thanks,
> Ovidiu
> 
>>> Thanks :)
>>>
>>> Maxime
> 
Hi Maxime, Ovidiu

I tested patch 5 alone on Agilex5 :)

Setup (back-to-back):

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
# DUT1: 172.16.3.1/24 on eth0.100.200
# DUT2: 172.16.3.2/24 on eth0.100.200
Results:

ethtool -K eth0 rx-vlan-offload off → QinQ ping PASS
ethtool -K eth0 rx-vlan-offload on → QinQ ping FAIL (100% loss)
ethtool -k eth0 shows rx-vlan-offload: on and rx-vlan-stag-hw-parse: on.

So the software VLAN path is fine, but with HW RX VLAN stripping 
enabled, patch 5 alone does not fix QinQ on this XGMAC. I will be happy 
to collect more data (tcpdump / RDES3 ET-LT) or try additional patches 
from the series if you have a preferred next step.

BR,
Nazim