net: dsa: tag_ocelot: create separate tagger for Seville

The ocelot tagger is a hot mess currently, it relies on memory
initialized by the attached driver for basic frame transmission.
This is against all that DSA tagging protocols stand for, which is that
the transmission and reception of a DSA-tagged frame, the data path,
should be independent from the switch control path, because the tag
protocol is in principle hot-pluggable and reusable across switches
(even if in practice it wasn't until very recently). But if another
driver like dsa_loop wants to make use of tag_ocelot, it couldn't.

This was done to have common code between Felix and Ocelot, which have
one bit difference in the frame header format. Quoting from commit
67c2404922c2 ("net: dsa: felix: create a template for the DSA tags on
xmit"):

    Other alternatives have been analyzed, such as:
    - Create a separate tag_seville.c: too much code duplication for just 1
      bit field difference.
    - Create a separate DSA_TAG_PROTO_SEVILLE under tag_ocelot.c, just like
      tag_brcm.c, which would have a separate .xmit function. Again, too
      much code duplication for just 1 bit field difference.
    - Allocate the template from the init function of the tag_ocelot.c
      module, instead of from the driver: couldn't figure out a method of
      accessing the correct port template corresponding to the correct
      tagger in the .xmit function.

The really interesting part is that Seville should have had its own
tagging protocol defined - it is not compatible on the wire with Ocelot,
even for that single bit. In principle, a packet generated by
DSA_TAG_PROTO_OCELOT when booted on NXP LS1028A would look in a certain
way, but when booted on NXP T1040 it would look differently. The reverse
is also true: a packet generated by a Seville switch would be
interpreted incorrectly by Wireshark if it was told it was generated by
an Ocelot switch.

Actually things are a bit more nuanced. If we concentrate only on the
DSA tag, what I said above is true, but Ocelot/Seville also support an
optional DSA tag prefix, which can be short or long, and it is possible
to distinguish the two taggers based on an integer constant put in that
prefix. Nonetheless, creating a separate tagger is still justified,
since the tag prefix is optional, and without it, there is again no way
to distinguish.

Claiming backwards binary compatibility is a bit more tough, since I've
already changed the format of tag_ocelot once, in commit 5124197ce58b
("net: dsa: tag_ocelot: use a short prefix on both ingress and egress").
Therefore I am not very concerned with treating this as a bugfix and
backporting it to stable kernels (which would be another mess due to the
fact that there would be lots of conflicts with the other DSA_TAG_PROTO*
definitions). It's just simpler to say that the string values of the
taggers have ABI value starting with kernel 5.12, which will be when the
changing of tag protocol via /sys/class/net/<dsa-master>/dsa/tagging
goes live.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 53 insertions, 15 deletions

diff --git a/net/dsa/tag_ocelot.c b/net/dsa/tag_ocelot.c
index fe00519229d7..a7dd61c8e005 100644
--- a/net/dsa/tag_ocelot.c
+++ b/net/dsa/tag_ocelot.c
@@ -24,33 +24,52 @@ static void ocelot_xmit_ptp(struct dsa_port *dp, void *injection,
 	ocelot_ifh_set_rew_op(injection, rew_op);
 }
 
-static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
-				   struct net_device *netdev)
+static void ocelot_xmit_common(struct sk_buff *skb, struct net_device *netdev,
+			       __be32 ifh_prefix, void **ifh)
 {
 	struct dsa_port *dp = dsa_slave_to_port(netdev);
 	struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
 	struct dsa_switch *ds = dp->ds;
-	struct ocelot *ocelot = ds->priv;
-	struct ocelot_port *ocelot_port;
-	u8 *prefix, *injection;
-
-	ocelot_port = ocelot->ports[dp->index];
+	void *injection;
+	__be32 *prefix;
 
 	injection = skb_push(skb, OCELOT_TAG_LEN);
-
 	prefix = skb_push(skb, OCELOT_SHORT_PREFIX_LEN);
 
-	memcpy(prefix, ocelot_port->xmit_template, OCELOT_TOTAL_TAG_LEN);
-
-	/* Fix up the fields which are not statically determined
-	 * in the template
-	 */
+	*prefix = ifh_prefix;
+	memset(injection, 0, OCELOT_TAG_LEN);
+	ocelot_ifh_set_bypass(injection, 1);
+	ocelot_ifh_set_src(injection, ds->num_ports);
 	ocelot_ifh_set_qos_class(injection, skb->priority);
 
 	/* TX timestamping was requested */
 	if (clone)
 		ocelot_xmit_ptp(dp, injection, clone);
 
+	*ifh = injection;
+}
+
+static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
+				   struct net_device *netdev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(netdev);
+	void *injection;
+
+	ocelot_xmit_common(skb, netdev, cpu_to_be32(0x8880000a), &injection);
+	ocelot_ifh_set_dest(injection, BIT(dp->index));
+
+	return skb;
+}
+
+static struct sk_buff *seville_xmit(struct sk_buff *skb,
+				    struct net_device *netdev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(netdev);
+	void *injection;
+
+	ocelot_xmit_common(skb, netdev, cpu_to_be32(0x88800005), &injection);
+	seville_ifh_set_dest(injection, BIT(dp->index));
+
 	return skb;
 }
 
@@ -147,7 +166,26 @@ static const struct dsa_device_ops ocelot_netdev_ops = {
 	.promisc_on_master	= true,
 };
 
-MODULE_LICENSE("GPL v2");
+DSA_TAG_DRIVER(ocelot_netdev_ops);
 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_OCELOT);
 
-module_dsa_tag_driver(ocelot_netdev_ops);
+static const struct dsa_device_ops seville_netdev_ops = {
+	.name			= "seville",
+	.proto			= DSA_TAG_PROTO_SEVILLE,
+	.xmit			= seville_xmit,
+	.rcv			= ocelot_rcv,
+	.overhead		= OCELOT_TOTAL_TAG_LEN,
+	.promisc_on_master	= true,
+};
+
+DSA_TAG_DRIVER(seville_netdev_ops);
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_SEVILLE);
+
+static struct dsa_tag_driver *ocelot_tag_driver_array[] = {
+	&DSA_TAG_DRIVER_NAME(ocelot_netdev_ops),
+	&DSA_TAG_DRIVER_NAME(seville_netdev_ops),
+};
+
+module_dsa_tag_drivers(ocelot_tag_driver_array);
+
+MODULE_LICENSE("GPL v2");