[PATCH v3 net-next 10/17] net: dsa: sja1105: Build a minimal understanding of meta frames

[Vladimir Oltean <olteanv@gmail.com>]

Meta frames are sent on the CPU port by the switch if RX timestamping is
enabled. They contain a partial timestamp of the previous frame.

They are Ethernet frames with the Ethernet header constructed out of:

- SJA1105_META_DMAC
- SJA1105_META_SMAC
- ETH_P_SJA1105_META

The Ethernet payload will be decoded in a follow-up patch.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
---
Changes in v3:

Split from previous 09/10 patch (no functional changes).

Changes in v2:

None.

 include/linux/dsa/sja1105.h | 11 +++++++++++
 net/dsa/tag_sja1105.c       | 15 +++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/dsa/sja1105.h b/include/linux/dsa/sja1105.h
index f5d5f7823da6..4f09743b4713 100644
--- a/include/linux/dsa/sja1105.h
+++ b/include/linux/dsa/sja1105.h
@@ -12,6 +12,7 @@
 #include <net/dsa.h>
 
 #define ETH_P_SJA1105				ETH_P_DSA_8021Q
+#define ETH_P_SJA1105_META			0x0008
 
 /* IEEE 802.3 Annex 57A: Slow Protocols PDUs (01:80:C2:xx:xx:xx) */
 #define SJA1105_LINKLOCAL_FILTER_A		0x0180C2000000ull
@@ -20,6 +21,16 @@
 #define SJA1105_LINKLOCAL_FILTER_B		0x011B19000000ull
 #define SJA1105_LINKLOCAL_FILTER_B_MASK		0xFFFFFF000000ull
 
+/* Source and Destination MAC of follow-up meta frames.
+ * Whereas the choice of SMAC only affects the unique identification of the
+ * switch as sender of meta frames, the DMAC must be an address that is present
+ * in the DSA master port's multicast MAC filter.
+ * 01-80-C2-00-00-0E is a good choice for this, as all profiles of IEEE 1588
+ * over L2 use this address for some purpose already.
+ */
+#define SJA1105_META_SMAC			0x222222222222ull
+#define SJA1105_META_DMAC			0x0180C200000Eull
+
 struct sja1105_port {
 	struct dsa_port *dp;
 	bool hwts_tx_en;
diff --git a/net/dsa/tag_sja1105.c b/net/dsa/tag_sja1105.c
index 7a56a27a1fd2..9ff7cfa6ea20 100644
--- a/net/dsa/tag_sja1105.c
+++ b/net/dsa/tag_sja1105.c
@@ -7,6 +7,21 @@
 #include <linux/packing.h>
 #include "dsa_priv.h"
 
+static inline bool sja1105_is_meta_frame(const struct sk_buff *skb)
+{
+	const struct ethhdr *hdr = eth_hdr(skb);
+	u64 smac = ether_addr_to_u64(hdr->h_source);
+	u64 dmac = ether_addr_to_u64(hdr->h_dest);
+
+	if (smac != SJA1105_META_SMAC)
+		return false;
+	if (dmac != SJA1105_META_DMAC)
+		return false;
+	if (ntohs(hdr->h_proto) != ETH_P_SJA1105_META)
+		return false;
+	return true;
+}
+
 /* 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.
-- 
2.17.1