[RFC PATCH 1/9] net: dsa: Add tag handling for Hirschmann Hellcreek switches

[Kurt Kanzenbach <kurt@linutronix.de>]

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>
---
 include/net/dsa.h       |   2 +
 net/dsa/Kconfig         |   6 +++
 net/dsa/Makefile        |   1 +
 net/dsa/tag_hellcreek.c | 101 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 110 insertions(+)
 create mode 100644 net/dsa/tag_hellcreek.c

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 50389772c597..2784c4851d92 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -44,6 +44,7 @@ struct phylink_link_state;
 #define DSA_TAG_PROTO_KSZ8795_VALUE		14
 #define DSA_TAG_PROTO_OCELOT_VALUE		15
 #define DSA_TAG_PROTO_AR9331_VALUE		16
+#define DSA_TAG_PROTO_HELLCREEK_VALUE		17
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -63,6 +64,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_KSZ8795		= DSA_TAG_PROTO_KSZ8795_VALUE,
 	DSA_TAG_PROTO_OCELOT		= DSA_TAG_PROTO_OCELOT_VALUE,
 	DSA_TAG_PROTO_AR9331		= DSA_TAG_PROTO_AR9331_VALUE,
+	DSA_TAG_PROTO_HELLCREEK		= DSA_TAG_PROTO_HELLCREEK_VALUE,
 };
 
 struct packet_type;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index d5bc6ac599ef..edc0c3ab6a4e 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -121,4 +121,10 @@ config NET_DSA_TAG_TRAILER
 	  Say Y or M if you want to enable support for tagging frames at
 	  with a trailed. e.g. Marvell 88E6060.
 
+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.
+
 endif
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index 108486cfdeef..ed72f4ea899b 100644
--- a/net/dsa/Makefile
+++ b/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-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o
 obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o
diff --git a/net/dsa/tag_hellcreek.c b/net/dsa/tag_hellcreek.c
new file mode 100644
index 000000000000..0895eda94bb5
--- /dev/null
+++ b/net/dsa/tag_hellcreek.c
@@ -0,0 +1,101 @@
+// 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);
+	struct sk_buff *nskb;
+	int padlen;
+	u8 *tag;
+
+	padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len;
+
+	if (skb_tailroom(skb) >= padlen + HELLCREEK_TAG_LEN) {
+		/* Let dsa_slave_xmit() free skb */
+		if (__skb_put_padto(skb, skb->len + padlen, false))
+			return NULL;
+
+		nskb = skb;
+	} else {
+		nskb = alloc_skb(NET_IP_ALIGN + skb->len +
+				 padlen + HELLCREEK_TAG_LEN, GFP_ATOMIC);
+		if (!nskb)
+			return NULL;
+		skb_reserve(nskb, NET_IP_ALIGN);
+
+		skb_reset_mac_header(nskb);
+		skb_set_network_header(nskb,
+				       skb_network_header(skb) - skb->head);
+		skb_set_transport_header(nskb,
+					 skb_transport_header(skb) - skb->head);
+		skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
+
+		/* Let skb_put_padto() free nskb, and let dsa_slave_xmit() free
+		 * skb
+		 */
+		if (skb_put_padto(nskb, nskb->len + padlen))
+			return NULL;
+
+		consume_skb(skb);
+	}
+
+	if (!nskb)
+		return NULL;
+
+	/* Tag encoding */
+	tag  = skb_put(nskb, HELLCREEK_TAG_LEN);
+	*tag = BIT(dp->index);
+
+	return nskb;
+}
+
+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,
+};
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_HELLCREEK);
+
+module_dsa_tag_driver(hellcreek_netdev_ops);
-- 
2.20.1