net: dsa: Add tag handling for Hirschmann Hellcreek switches

The Hirschmann Hellcreek TSN switches have a special tagging protocol for frames
exchanged between the CPU port and the master interface. The format is a one
byte trailer indicating the destination or origin port.

It's quite similar to the Micrel KSZ tagging. That's why the implementation is
based on that code.
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/dsa.h

@@ -45,6 +45,7 @@ struct phylink_link_state;
 #define DSA_TAG_PROTO_OCELOT_VALUE		15
 #define DSA_TAG_PROTO_AR9331_VALUE		16
 #define DSA_TAG_PROTO_RTL4_A_VALUE		17
+#define DSA_TAG_PROTO_HELLCREEK_VALUE		18
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -65,6 +66,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_OCELOT		= DSA_TAG_PROTO_OCELOT_VALUE,
 	DSA_TAG_PROTO_AR9331		= DSA_TAG_PROTO_AR9331_VALUE,
 	DSA_TAG_PROTO_RTL4_A		= DSA_TAG_PROTO_RTL4_A_VALUE,
+	DSA_TAG_PROTO_HELLCREEK		= DSA_TAG_PROTO_HELLCREEK_VALUE,
 };
 
 struct packet_type;

net/dsa/Kconfig

@@ -56,6 +56,12 @@ config NET_DSA_TAG_BRCM_PREPEND
 	  Broadcom switches which places the tag before the Ethernet header
 	  (prepended).
 
+config NET_DSA_TAG_HELLCREEK
+	tristate "Tag driver for Hirschmann Hellcreek TSN switches"
+	help
+	  Say Y or M if you want to enable support for tagging frames
+	  for the Hirschmann Hellcreek TSN switches.
+
 config NET_DSA_TAG_GSWIP
 	tristate "Tag driver for Lantiq / Intel GSWIP switches"
 	help

net/dsa/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_NET_DSA_TAG_BRCM_COMMON) += tag_brcm.o
 obj-$(CONFIG_NET_DSA_TAG_DSA) += tag_dsa.o
 obj-$(CONFIG_NET_DSA_TAG_EDSA) += tag_edsa.o
 obj-$(CONFIG_NET_DSA_TAG_GSWIP) += tag_gswip.o
+obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o
 obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o
 obj-$(CONFIG_NET_DSA_TAG_RTL4_A) += tag_rtl4_a.o
 obj-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o

net/dsa/tag_hellcreek.c

+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/*
+ * net/dsa/tag_hellcreek.c - Hirschmann Hellcreek switch tag format handling
+ *
+ * Copyright (C) 2019,2020 Linutronix GmbH
+ * Author Kurt Kanzenbach <kurt@linutronix.de>
+ *
+ * Based on tag_ksz.c.
+ */
+
+#include <linux/etherdevice.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <net/dsa.h>
+
+#include "dsa_priv.h"
+
+#define HELLCREEK_TAG_LEN	1
+
+static struct sk_buff *hellcreek_xmit(struct sk_buff *skb,
+				      struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(dev);
+	u8 *tag;
+
+	/* Tag encoding */
+	tag  = skb_put(skb, HELLCREEK_TAG_LEN);
+	*tag = BIT(dp->index);
+
+	return skb;
+}
+
+static struct sk_buff *hellcreek_rcv(struct sk_buff *skb,
+				     struct net_device *dev,
+				     struct packet_type *pt)
+{
+	/* Tag decoding */
+	u8 *tag = skb_tail_pointer(skb) - HELLCREEK_TAG_LEN;
+	unsigned int port = tag[0] & 0x03;
+
+	skb->dev = dsa_master_find_slave(dev, 0, port);
+	if (!skb->dev) {
+		netdev_warn(dev, "Failed to get source port: %d\n", port);
+		return NULL;
+	}
+
+	pskb_trim_rcsum(skb, skb->len - HELLCREEK_TAG_LEN);
+
+	skb->offload_fwd_mark = true;
+
+	return skb;
+}
+
+static const struct dsa_device_ops hellcreek_netdev_ops = {
+	.name	  = "hellcreek",
+	.proto	  = DSA_TAG_PROTO_HELLCREEK,
+	.xmit	  = hellcreek_xmit,
+	.rcv	  = hellcreek_rcv,
+	.overhead = HELLCREEK_TAG_LEN,
+	.tail_tag = true,
+};
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_HELLCREEK);
+
+module_dsa_tag_driver(hellcreek_netdev_ops);