[PATCH RFC net 1/2] net: dsa: provide a way to exclude switch ports from VLAN untagging

[Robert Hodaszi <robert.hodaszi@digi.com>]

Even if a switch driver sets 'untag_vlan_aware_bridge_pvid' or
'untag_bridge_pvid', it may not enable tagging on one or more ports
(VLAN-unaware port). Without a way to exclude these ports,
dsa_software_vlan_untag() untags packets it shouldn't, and so it
corrupts the packet.

That happens currently with the felix driver. The driver always sets
'untag_vlan_aware_bridge_pvid', but enables inner tags
(push_inner_tag=1) only when VLAN-filtering is enabled.

To exclude a port from untagging, set dp->not_tagged=1. The inverse
logic is to keep backward compatibility, and avoid the need to
potentially change currently working users.

Fixes: f1288fd7293b ("net: dsa: felix: fix VLAN tag loss on CPU reception with ocelot-8021q")
Signed-off-by: Robert Hodaszi <robert.hodaszi@digi.com>
---
 include/net/dsa.h | 7 +++++++
 net/dsa/tag.h     | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 72ae65e7246a..99b1267f0c46 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -289,6 +289,13 @@ struct dsa_port {
 
 	u8			setup:1;
 
+	/* Use this to mark a switch port as "untagged", to avoid
+	 * dsa_software_vlan_untag() do a VLAN untagging on it if
+	 * ds->untag_bridge_pvid or ds->untag_vlan_aware_bridge_pvid is set to
+	 * true
+	 */
+	u8			not_tagged:1;
+
 	struct device_node	*dn;
 	unsigned int		ageing_time;
 
diff --git a/net/dsa/tag.h b/net/dsa/tag.h
index d5707870906b..c3d76a49b1c6 100644
--- a/net/dsa/tag.h
+++ b/net/dsa/tag.h
@@ -155,6 +155,10 @@ static inline struct sk_buff *dsa_software_vlan_untag(struct sk_buff *skb)
 	if (!br)
 		return skb;
 
+	/* This switch port is not tagged, no need for untagging */
+	if (dp->not_tagged)
+		return skb;
+
 	/* Move VLAN tag from data to hwaccel */
 	if (!skb_vlan_tag_present(skb)) {
 		skb = skb_vlan_untag(skb);
-- 
2.43.0