[PATCH] wifi: ath12k: set OFFLOAD_ENCAP_4ADDR on interface bringup

[Ronald Ouyang <repaxan@gmail.com>]

I tried the WDS support added in https://lists.infradead.org/pipermail/ath12k/2026-May/009382.html.
With a ath12k WDS client, the frames received by the WDS AP had some extra bytes in the beginning of the frame.

My understanding of the problem:
1 - this is a WDS client, 4 address mode.
2 - on interface bringup (ath12k_mac_op_add_interface), it has OFFLOAD_ENCAP_ENABLED but not OFFLOAD_ENCAP_4ADDR.
    so it software encaps the ethernet frames and sends the resulting wifi frames to the vdev
3 - on vdev bringup (ath12k_mac_vdev_create -> ath12k_mac_update_vif_offload), it has OFFLOAD_ENCAP_ENABLED.
    so it expects to receive ethernet or "native wifi" frames.
    it also sets OFFLOAD_ENCAP_4ADDR but it's too late here
4 - the wifi frame from (2) gets passed to the vdev marked as "native wifi".
    it already had a QOS field in it, the vdev adds an extra one when doing the hardware encap

This fixes it by setting OFFLOAD_ENCAP_4ADDR during interface bringup.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.6-01243-QCAHKSWPL_SILICONZ-1
Fixes: 729cad3c3c9e ("wifi: ath12k: Add 4-address mode support for eth offload")

Signed-off-by: Ronald Ouyang <repaxan@gmail.com>
---
 drivers/net/wireless/ath/ath12k/mac.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath12k/mac.c b/drivers/net/wireless/ath/ath12k/mac.c
index afa3556480d3..1b1c3f738590 100644
--- a/drivers/net/wireless/ath/ath12k/mac.c
+++ b/drivers/net/wireless/ath/ath12k/mac.c
@@ -10275,7 +10275,8 @@ static void ath12k_mac_update_vif_offload(struct ath12k_link_vif *arvif)
 	if (ret) {
 		ath12k_warn(ab, "failed to set vdev %d tx encap mode: %d\n",
 			    arvif->vdev_id, ret);
-		vif->offload_flags &= ~IEEE80211_OFFLOAD_ENCAP_ENABLED;
+		vif->offload_flags &= ~(IEEE80211_OFFLOAD_ENCAP_ENABLED |
+					IEEE80211_OFFLOAD_ENCAP_4ADDR);
 	}
 
 	if (vif->offload_flags & IEEE80211_OFFLOAD_ENCAP_ENABLED)
@@ -10939,6 +10940,9 @@ int ath12k_mac_op_add_interface(struct ieee80211_hw *hw,
 
 	vif->driver_flags |= IEEE80211_VIF_SUPPORTS_UAPSD;
 
+	if (vif->offload_flags & IEEE80211_OFFLOAD_ENCAP_ENABLED)
+		vif->offload_flags |= IEEE80211_OFFLOAD_ENCAP_4ADDR;
+
 	ath12k_mac_determine_vdev_type(vif, ahvif);
 
 	for_each_ar(ah, ar, i) {
-- 
2.56.1