net: dsa: sja1105: Receive and decode meta frames

This adds support in the tagger for understanding the source port and
switch id of meta frames.  Their timestamp is also extracted but not
used yet - this needs to be done in a state machine that modifies the
previously received timestampable frame - will be added in a follow-up
patch.

Also take the opportunity to:
- Remove a comment in sja1105_filter made obsolete by e8d67fa5
  ("net: dsa: sja1105: Don't store frame type in skb->cb")
- Reorder the checks in sja1105_filter to optimize for the most likely
  scenario first: regular traffic.
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_sja1105.c

@@ -24,6 +24,36 @@ static inline bool sja1105_is_link_local(const struct sk_buff *skb)
 	return false;
 }
 
+struct sja1105_meta {
+	u64 tstamp;
+	u64 dmac_byte_4;
+	u64 dmac_byte_3;
+	u64 source_port;
+	u64 switch_id;
+};
+
+static void sja1105_meta_unpack(const struct sk_buff *skb,
+				struct sja1105_meta *meta)
+{
+	u8 *buf = skb_mac_header(skb) + ETH_HLEN;
+
+	/* UM10944.pdf section 4.2.17 AVB Parameters:
+	 * Structure of the meta-data follow-up frame.
+	 * It is in network byte order, so there are no quirks
+	 * while unpacking the meta frame.
+	 *
+	 * Also SJA1105 E/T only populates bits 23:0 of the timestamp
+	 * whereas P/Q/R/S does 32 bits. Since the structure is the
+	 * same and the E/T puts zeroes in the high-order byte, use
+	 * a unified unpacking command for both device series.
+	 */
+	packing(buf,     &meta->tstamp,     31, 0, 4, UNPACK, 0);
+	packing(buf + 4, &meta->dmac_byte_4, 7, 0, 1, UNPACK, 0);
+	packing(buf + 5, &meta->dmac_byte_3, 7, 0, 1, UNPACK, 0);
+	packing(buf + 6, &meta->source_port, 7, 0, 1, UNPACK, 0);
+	packing(buf + 7, &meta->switch_id,   7, 0, 1, UNPACK, 0);
+}
+
 static inline bool sja1105_is_meta_frame(const struct sk_buff *skb)
 {
 	const struct ethhdr *hdr = eth_hdr(skb);
@@ -40,14 +70,15 @@ static inline bool sja1105_is_meta_frame(const struct sk_buff *skb)
 }
 
 /* This is the first time the tagger sees the frame on RX.
- * Figure out if we can decode it, and if we can, annotate skb->cb with how we
- * plan to do that, so we don't need to check again in the rcv function.
+ * Figure out if we can decode it.
  */
 static bool sja1105_filter(const struct sk_buff *skb, struct net_device *dev)
 {
+	if (!dsa_port_is_vlan_filtering(dev->dsa_ptr))
+		return true;
 	if (sja1105_is_link_local(skb))
 		return true;
-	if (!dsa_port_is_vlan_filtering(dev->dsa_ptr))
+	if (sja1105_is_meta_frame(skb))
 		return true;
 	return false;
 }
@@ -83,16 +114,19 @@ static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
 				   struct net_device *netdev,
 				   struct packet_type *pt)
 {
+	struct sja1105_meta meta = {0};
 	int source_port, switch_id;
 	struct vlan_ethhdr *hdr;
 	u16 tpid, vid, tci;
 	bool is_link_local;
 	bool is_tagged;
+	bool is_meta;
 
 	hdr = vlan_eth_hdr(skb);
 	tpid = ntohs(hdr->h_vlan_proto);
 	is_tagged = (tpid == ETH_P_SJA1105);
 	is_link_local = sja1105_is_link_local(skb);
+	is_meta = sja1105_is_meta_frame(skb);
 
 	skb->offload_fwd_mark = 1;
 
@@ -113,6 +147,10 @@ static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
 		/* Clear the DMAC bytes that were mangled by the switch */
 		hdr->h_dest[3] = 0;
 		hdr->h_dest[4] = 0;
+	} else if (is_meta) {
+		sja1105_meta_unpack(skb, &meta);
+		source_port = meta.source_port;
+		switch_id = meta.switch_id;
 	} else {
 		return NULL;
 	}