[PATCH v2] net: dsa: push hwaccel VLAN tag into payload in dsa_user_xmit()
WARM1d
From: Amitesh Singh <hidden>
Date: 2026-09-30 03:33:12
Also in:
lkml
Subsystem:
networking [dsa], networking [general], the rest · Maintainers:
Andrew Lunn, Vladimir Oltean, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
When a socket buffer has a hardware-accelerated VLAN tag (skb->vlan_tci set), the conduit NIC inserts the 802.1Q header after whatever the DSA tagger prepends, producing the wrong on-wire ordering: [tagger header][802.1Q VID] instead of the correct: [802.1Q VID][tagger header] (for taggers that follow the VLAN) [tagger header][802.1Q VID] (for taggers that precede the VLAN — broken) This affects any platform where tx-vlan-offload is enabled or fixed:on and cannot be disabled (e.g. imx-dwmac). tag_rtl8_4 and tag_sja1105 both carried open-coded workarounds for this; rather than let each new tagger rediscover the problem, handle it once in dsa_user_xmit() before the skb is handed to any tagger. __vlan_hwaccel_push_inside() frees the skb internally on allocation failure, so returning NETDEV_TX_OK on NULL is correct. Remove the now-redundant per-tagger copies from tag_rtl8_4.c and tag_sja1105.c. Note: tag_lan9303.c is unaffected. Its xmit path never inspects skb->vlan_tci — it always writes its own fixed [8100 | port_index] header regardless. The skb_vlan_tag_present() call in lan9303_rcv is on the RX path, which this change does not touch. Signed-off-by: Amitesh Singh <redacted> --- net/dsa/tag_sja1105.c | 10 ---------- net/dsa/user.c | 13 +++++++++++++ 2 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/net/dsa/tag_sja1105.c b/net/dsa/tag_sja1105.c
index bfe1f746f55b..57bb9360f9d2 100644
--- a/net/dsa/tag_sja1105.c
+++ b/net/dsa/tag_sja1105.c@@ -244,16 +244,6 @@ static struct sk_buff *sja1105_pvid_tag_control_pkt(struct dsa_port *dp, __be16 xmit_tpid = htons(sja1105_xmit_tpid(dp)); struct vlan_ethhdr *hdr; - /* If VLAN tag is in hwaccel area, move it to the payload - * to deal with both cases uniformly and to ensure that - * the VLANs are added in the right order. - */ - if (unlikely(skb_vlan_tag_present(skb))) { - skb = __vlan_hwaccel_push_inside(skb); - if (!skb) - return NULL; - } - hdr = skb_vlan_eth_hdr(skb); /* If skb is already VLAN-tagged, leave that VLAN ID in place */
diff --git a/net/dsa/user.c b/net/dsa/user.c
index 041f9060c8ef..7c178634228c 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c@@ -20,6 +20,7 @@ #include <net/tc_act/tc_mirred.h> #include <linux/if_bridge.h> #include <linux/if_hsr.h> +#include <linux/if_vlan.h> #include <net/dcbnl.h> #include <linux/netpoll.h> #include <linux/string.h>
@@ -935,6 +936,18 @@ static netdev_tx_t dsa_user_xmit(struct sk_buff *skb, struct net_device *dev) if (dev->needed_tailroom) eth_skb_pad(skb); + /* If the conduit NIC has tx-vlan-offload enabled (or it is fixed:on and + * cannot be turned off, e.g. imx-dwmac), it will insert the 802.1Q + * header *after* whatever the tagger prepends, producing the wrong + * on-wire ordering. Materialise any hwaccel VLAN tag into the payload + * here, once, before handing the skb to the tagger. + */ + if (skb_vlan_tag_present(skb)) { + skb = __vlan_hwaccel_push_inside(skb); + if (!skb) + return NETDEV_TX_OK; + } + /* Transmit function may have to reallocate the original SKB, * in which case it must have freed it. Taggers will drop the * passed skb on error.
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2.43.0