net: dsa: tag_ksz: add tag handling for Microchip LAN937x

The Microchip LAN937X switches have a tagging protocol which is
very similar to KSZ tagging. So that the implementation is added to
tag_ksz.c and reused common APIs

Signed-off-by: Prasanna Vengateshan <[e-mail]>
Signed-off-by: Arun Ramadoss <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/dsa.h

···
 #define DSA_TAG_PROTO_RTL8_4_VALUE		24
 #define DSA_TAG_PROTO_RTL8_4T_VALUE		25
 #define DSA_TAG_PROTO_RZN1_A5PSW_VALUE		26
+#define DSA_TAG_PROTO_LAN937X_VALUE		27
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
···
 	DSA_TAG_PROTO_RTL8_4		= DSA_TAG_PROTO_RTL8_4_VALUE,
 	DSA_TAG_PROTO_RTL8_4T		= DSA_TAG_PROTO_RTL8_4T_VALUE,
 	DSA_TAG_PROTO_RZN1_A5PSW	= DSA_TAG_PROTO_RZN1_A5PSW_VALUE,
+	DSA_TAG_PROTO_LAN937X		= DSA_TAG_PROTO_LAN937X_VALUE,
 };
 
 struct dsa_switch;

net/dsa/Kconfig

···
 	  Mediatek switches.
 
 config NET_DSA_TAG_KSZ
-	tristate "Tag driver for Microchip 8795/9477/9893 families of switches"
+	tristate "Tag driver for Microchip 8795/937x/9477/9893 families of switches"
 	help
 	  Say Y if you want to enable support for tagging frames for the
-	  Microchip 8795/9477/9893 families of switches.
+	  Microchip 8795/937x/9477/9893 families of switches.
 
 config NET_DSA_TAG_OCELOT
 	tristate "Tag driver for Ocelot family of switches, using NPI port"

net/dsa/tag_ksz.c

···
 DSA_TAG_DRIVER(ksz9893_netdev_ops);
 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_KSZ9893);
 
+/* For xmit, 2 bytes are added before FCS.
+ * ---------------------------------------------------------------------------
+ * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|tag1(1byte)|FCS(4bytes)
+ * ---------------------------------------------------------------------------
+ * tag0 : represents tag override, lookup and valid
+ * tag1 : each bit represents port (eg, 0x01=port1, 0x02=port2, 0x80=port8)
+ *
+ * For rcv, 1 byte is added before FCS.
+ * ---------------------------------------------------------------------------
+ * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|FCS(4bytes)
+ * ---------------------------------------------------------------------------
+ * tag0 : zero-based value represents port
+ *	  (eg, 0x00=port1, 0x02=port3, 0x07=port8)
+ */
+#define LAN937X_EGRESS_TAG_LEN		2
+
+#define LAN937X_TAIL_TAG_BLOCKING_OVERRIDE	BIT(11)
+#define LAN937X_TAIL_TAG_LOOKUP			BIT(12)
+#define LAN937X_TAIL_TAG_VALID			BIT(13)
+#define LAN937X_TAIL_TAG_PORT_MASK		7
+
+static struct sk_buff *lan937x_xmit(struct sk_buff *skb,
+				    struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(dev);
+	const struct ethhdr *hdr = eth_hdr(skb);
+	__be16 *tag;
+	u16 val;
+
+	if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
+		return NULL;
+
+	tag = skb_put(skb, LAN937X_EGRESS_TAG_LEN);
+
+	val = BIT(dp->index);
+
+	if (is_link_local_ether_addr(hdr->h_dest))
+		val |= LAN937X_TAIL_TAG_BLOCKING_OVERRIDE;
+
+	/* Tail tag valid bit - This bit should always be set by the CPU */
+	val |= LAN937X_TAIL_TAG_VALID;
+
+	put_unaligned_be16(val, tag);
+
+	return skb;
+}
+
+static const struct dsa_device_ops lan937x_netdev_ops = {
+	.name	= "lan937x",
+	.proto	= DSA_TAG_PROTO_LAN937X,
+	.xmit	= lan937x_xmit,
+	.rcv	= ksz9477_rcv,
+	.needed_tailroom = LAN937X_EGRESS_TAG_LEN,
+};
+
+DSA_TAG_DRIVER(lan937x_netdev_ops);
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_LAN937X);
+
 static struct dsa_tag_driver *dsa_tag_driver_array[] = {
 	&DSA_TAG_DRIVER_NAME(ksz8795_netdev_ops),
 	&DSA_TAG_DRIVER_NAME(ksz9477_netdev_ops),
 	&DSA_TAG_DRIVER_NAME(ksz9893_netdev_ops),
+	&DSA_TAG_DRIVER_NAME(lan937x_netdev_ops),
 };
 
 module_dsa_tag_drivers(dsa_tag_driver_array);