Merge branch 'net-stmmac-fix-double-vlan-802-1ad-tag-handling'

Ovidiu Panait says:

====================
net: stmmac: Fix double VLAN 802.1ad tag handling

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 --

Note that this series only fixes the issue on dwmac4. dwxgmac2 has the same
issue but I do not have access to hw to test on.

Since dwmac4 does not expose the tag type in the RDES3 descriptor, it
cannot support hardware S-Tag stripping correctly. This series
disables S-tag stripping for it, so the 802.1ad tags are left in
place and are handled by the software VLAN path.
====================

Link: https://patch.msgid.link/20260928203441.34876-1-ovidiu.panait.rb@renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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