[PATCH net-next 4/6] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

["Alvin Šipraga" <alvin@pqrs.dk>]

From: Alvin Šipraga <alsi@bang-olufsen.dk>

This commit implements a basic version of the 8 byte tag protocol used
in the Realtek RTL8365MB-VC unmanaged switch, which carries with it a
protocol version of 0x04.

The implementation itself only handles the parsing of the EtherType
value and Realtek protocol version, together with the source or
destination port fields. The rest is left unimplemented for now.

The tag format is described in a confidential document provided to my
company by Realtek Semiconductor Corp. Permission has been granted by
the vendor to publish this driver based on that material, together with
an extract from the document describing the tag format and its fields.
It is hoped that this will help future implementors who do not have
access to the material but who wish to extend the functionality of
drivers for chips which use this protocol.

In addition, two possible values of the REASON field are specified,
based on experiments on my end. Realtek does not specify what value this
field can take.

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
---

RFC -> v1:
  - minor changes to the big comment at the top, including some
    empirical information about the REASON code
  - use dev_*_ratelimited() instead of netdev_*() for logging
  - use warning instead of debug messages
  - use ETH_P_REALTEK from if_ether.h
  - set LEARN_DIS on xmit
  - remove superfluous variables/expressions and use __b16 for tag
    variable
  - use new helper functions to insert/remove CPU tag
  - set offload_fwd_mark properly using helper function

 include/net/dsa.h    |   2 +
 net/dsa/Kconfig      |   6 ++
 net/dsa/Makefile     |   1 +
 net/dsa/tag_rtl8_4.c | 166 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 175 insertions(+)
 create mode 100644 net/dsa/tag_rtl8_4.c

diff --git a/include/net/dsa.h b/include/net/dsa.h
index d784e76113b8..783060e851a9 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -51,6 +51,7 @@ struct phylink_link_state;
 #define DSA_TAG_PROTO_SEVILLE_VALUE		21
 #define DSA_TAG_PROTO_BRCM_LEGACY_VALUE		22
 #define DSA_TAG_PROTO_SJA1110_VALUE		23
+#define DSA_TAG_PROTO_RTL8_4_VALUE		24
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -77,6 +78,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_OCELOT_8021Q	= DSA_TAG_PROTO_OCELOT_8021Q_VALUE,
 	DSA_TAG_PROTO_SEVILLE		= DSA_TAG_PROTO_SEVILLE_VALUE,
 	DSA_TAG_PROTO_SJA1110		= DSA_TAG_PROTO_SJA1110_VALUE,
+	DSA_TAG_PROTO_RTL8_4		= DSA_TAG_PROTO_RTL8_4_VALUE,
 };
 
 struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 6c7f79e45886..57fc52b17d55 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -130,6 +130,12 @@ config NET_DSA_TAG_RTL4_A
 	  Realtek switches with 4 byte protocol A tags, sich as found in
 	  the Realtek RTL8366RB.
 
+config NET_DSA_TAG_RTL8_4
+	tristate "Tag driver for Realtek 8 byte protocol 4 tags"
+	help
+	  Say Y or M if you want to enable support for tagging frames for Realtek
+	  switches with 8 byte protocol 4 tags, such as the Realtek RTL8365MB-VC.
+
 config NET_DSA_TAG_LAN9303
 	tristate "Tag driver for SMSC/Microchip LAN9303 family of switches"
 	help
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index f78d537044db..9f75820e7c98 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -16,6 +16,7 @@ obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
 obj-$(CONFIG_NET_DSA_TAG_OCELOT_8021Q) += tag_ocelot_8021q.o
 obj-$(CONFIG_NET_DSA_TAG_QCA) += tag_qca.o
 obj-$(CONFIG_NET_DSA_TAG_RTL4_A) += tag_rtl4_a.o
+obj-$(CONFIG_NET_DSA_TAG_RTL8_4) += tag_rtl8_4.o
 obj-$(CONFIG_NET_DSA_TAG_SJA1105) += tag_sja1105.o
 obj-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o
 obj-$(CONFIG_NET_DSA_TAG_XRS700X) += tag_xrs700x.o
diff --git a/net/dsa/tag_rtl8_4.c b/net/dsa/tag_rtl8_4.c
new file mode 100644
index 000000000000..da22fd12b645
--- /dev/null
+++ b/net/dsa/tag_rtl8_4.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Handler for Realtek 8 byte switch tags
+ *
+ * Copyright (C) 2021 Alvin Šipraga <alsi@bang-olufsen.dk>
+ *
+ * NOTE: Currently only supports protocol "4" found in the RTL8365MB, hence
+ * named tag_rtl8_4.
+ *
+ * This tag header has the following format:
+ *
+ *  -------------------------------------------
+ *  | MAC DA | MAC SA | 8 byte tag | Type | ...
+ *  -------------------------------------------
+ *     _______________/            \______________________________________
+ *    /                                                                   \
+ *  0                                  7|8                                 15
+ *  |-----------------------------------+-----------------------------------|---
+ *  |                               (16-bit)                                | ^
+ *  |                       Realtek EtherType [0x8899]                      | |
+ *  |-----------------------------------+-----------------------------------| 8
+ *  |              (8-bit)              |              (8-bit)              |
+ *  |          Protocol [0x04]          |              REASON               | b
+ *  |-----------------------------------+-----------------------------------| y
+ *  |   (1)  | (1) | (2) |   (1)  | (3) | (1)  | (1) |    (1)    |   (5)    | t
+ *  | FID_EN |  X  | FID | PRI_EN | PRI | KEEP |  X  | LEARN_DIS |    X     | e
+ *  |-----------------------------------+-----------------------------------| s
+ *  |   (1)  |                       (15-bit)                               | |
+ *  |  ALLOW |                        TX/RX                                 | v
+ *  |-----------------------------------+-----------------------------------|---
+ *
+ * With the following field descriptions:
+ *
+ *    field      | description
+ *   ------------+-------------
+ *    Realtek    | 0x8899: indicates that this is a proprietary Realtek tag;
+ *     EtherType |         note that Realtek uses the same EtherType for
+ *               |         other incompatible tag formats (e.g. tag_rtl4_a.c)
+ *    Protocol   | 0x04: indicates that this tag conforms to this format
+ *    X          | reserved
+ *   ------------+-------------
+ *    REASON     | reason for forwarding packet to CPU
+ *               | 0: packet was forwarded or flooded to CPU
+ *               | 80: packet was trapped to CPU
+ *    FID_EN     | 1: packet has an FID
+ *               | 0: no FID
+ *    FID        | FID of packet (if FID_EN=1)
+ *    PRI_EN     | 1: force priority of packet
+ *               | 0: don't force priority
+ *    PRI        | priority of packet (if PRI_EN=1)
+ *    KEEP       | preserve packet VLAN tag format
+ *    LEARN_DIS  | don't learn the source MAC address of the packet
+ *    ALLOW      | 1: treat TX/RX field as an allowance port mask, meaning the
+ *               |    packet may only be forwarded to ports specified in the
+ *               |    mask
+ *               | 0: no allowance port mask, TX/RX field is the forwarding
+ *               |    port mask
+ *    TX/RX      | TX (switch->CPU): port number the packet was received on
+ *               | RX (CPU->switch): forwarding port mask (if ALLOW=0)
+ *               |                   allowance port mask (if ALLOW=1)
+ */
+
+#include <linux/bits.h>
+#include <linux/etherdevice.h>
+
+#include "dsa_priv.h"
+
+#define RTL8_4_TAG_LEN			8
+/* 0x04 = RTL8365MB DSA protocol
+ */
+#define RTL8_4_PROTOCOL_RTL8365MB	0x04
+
+static struct sk_buff *rtl8_4_tag_xmit(struct sk_buff *skb,
+				       struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(dev);
+	__be16 *tag;
+
+	/* Pad out so the (stripped) packet is at least 64 bytes long
+	 * (including FCS), otherwise the switch will drop the packet.
+	 * Then we need an additional 8 bytes for the Realtek tag.
+	 */
+	if (unlikely(__skb_put_padto(skb, ETH_ZLEN + RTL8_4_TAG_LEN, false)))
+		return NULL;
+
+	skb_push(skb, RTL8_4_TAG_LEN);
+
+	dsa_alloc_etype_header(skb, RTL8_4_TAG_LEN);
+	tag = dsa_etype_header_pos_tx(skb);
+
+	/* Set Realtek EtherType */
+	tag[0] = htons(ETH_P_REALTEK);
+
+	/* Set Protocol; zero REASON */
+	tag[1] = htons(RTL8_4_PROTOCOL_RTL8365MB << 8);
+
+	/* Zero FID_EN, FID, PRI_EN, PRI, KEEP; set LEARN_DIS */
+	tag[2] = htons(1 << 5);
+
+	/* Zero ALLOW; set RX (CPU->switch) forwarding port mask */
+	tag[3] = htons(BIT(dp->index));
+
+	return skb;
+}
+
+static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
+				      struct net_device *dev)
+{
+	__be16 *tag;
+	u16 etype;
+	u8 proto;
+	u8 port;
+
+	if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
+		return NULL;
+
+	tag = dsa_etype_header_pos_rx(skb);
+
+	/* Parse Realtek EtherType */
+	etype = ntohs(tag[0]);
+	if (unlikely(etype != ETH_P_REALTEK)) {
+		dev_warn_ratelimited(&dev->dev,
+				     "non-realtek ethertype 0x%04x\n", etype);
+		return NULL;
+	}
+
+	/* Parse Protocol */
+	proto = ntohs(tag[1]) >> 8;
+	if (unlikely(proto != RTL8_4_PROTOCOL_RTL8365MB)) {
+		dev_warn_ratelimited(&dev->dev,
+				     "unknown realtek protocol 0x%02x\n",
+				     proto);
+		return NULL;
+	}
+
+	/* Parse TX (switch->CPU) */
+	port = ntohs(tag[3]) & 0xf; /* Port number is the LSB 4 bits */
+	skb->dev = dsa_master_find_slave(dev, 0, port);
+	if (!skb->dev) {
+		dev_warn_ratelimited(&dev->dev,
+				     "could not find slave for port %d\n",
+				     port);
+		return NULL;
+	}
+
+	/* Remove tag and recalculate checksum */
+	skb_pull_rcsum(skb, RTL8_4_TAG_LEN);
+
+	dsa_strip_etype_header(skb, RTL8_4_TAG_LEN);
+
+	dsa_default_offload_fwd_mark(skb);
+
+	return skb;
+}
+
+static const struct dsa_device_ops rtl8_4_netdev_ops = {
+	.name = "rtl8_4",
+	.proto = DSA_TAG_PROTO_RTL8_4,
+	.xmit = rtl8_4_tag_xmit,
+	.rcv = rtl8_4_tag_rcv,
+	.needed_headroom = RTL8_4_TAG_LEN,
+};
+module_dsa_tag_driver(rtl8_4_netdev_ops);
+
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL8_4);
-- 
2.32.0