Re: [PATCH net v4 5/7] net: stmmac: Disable S-Tag processing on dwmac4

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi,

On 9/8/26 18:43, 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 a 802.1ad outer tag are incorrectly passed up the stack as
> having an 802.1Q tag. This causes QinQ ping between two hosts to fail.
> 
> vlan_rx_hw() is shared by dwxgmac2 and dwmac4: on dwxgmac2 the tag type
> is available in the RDES3 write-back descriptor (the ET_LT field), so the
> outer tag type can be determined based on that info. However, dwmac4
> doesn't seem to provide the tag type. The Length/Type field in RDES3 only
> indicates whether the packet is single or double-tagged, not which tag
> type was stripped.
> 
> Since dwmac4 cannot report the stripped tag type, it cannot support
> hardware S-Tag stripping correctly. Therefore, restrict the
> NETIF_F_HW_VLAN_STAG_RX and NETIF_F_HW_VLAN_STAG_FILTER advertisement
> to dwxgmac2 only.
> 
> With this, 802.1ad tags are left in place and handled by the software
> VLAN path.
> 
> Fixes: 750011e239a5 ("net: stmmac: Add support for HW-accelerated VLAN stripping")
> Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@renesas.com>

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime