net: dsa: tag_ocelot_8021q: break circular dependency with ocelot switch lib

Michael reported that when using the "ocelot-8021q" tagging protocol,
the switch driver module must be manually loaded before the tagging
protocol can be loaded/is available.

This appears to be the same problem described here:
https://lore.kernel.org/netdev/20210908220834.d7gmtnwrorhharna@skbuf/
where due to the fact that DSA tagging protocols make use of symbols
exported by the switch drivers, circular dependencies appear and this
breaks module autoloading.

The ocelot_8021q driver needs the ocelot_can_inject() and
ocelot_port_inject_frame() functions from the switch library. Previously
the wrong approach was taken to solve that dependency: shims were
provided for the case where the ocelot switch library was compiled out,
but that turns out to be insufficient, because the dependency when the
switch lib _is_ compiled is problematic too.

We cannot declare ocelot_can_inject() and ocelot_port_inject_frame() as
static inline functions, because these access I/O functions like
__ocelot_write_ix() which is called by ocelot_write_rix(). Making those
static inline basically means exposing the whole guts of the ocelot
switch library, not ideal...

We already have one tagging protocol driver which calls into the switch
driver during xmit but not using any exported symbol: sja1105_defer_xmit.
We can do the same thing here: create a kthread worker and one work item
per skb, and let the switch driver itself do the register accesses to
send the skb, and then consume it.

Fixes: 0a6f17c6ae21 ("net: dsa: tag_ocelot_8021q: add support for PTP timestamping")
Reported-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 25 insertions, 15 deletions

diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index d166377d7085..d8ee15f1c7a9 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -112,8 +112,6 @@ config NET_DSA_TAG_OCELOT
 
 config NET_DSA_TAG_OCELOT_8021Q
 	tristate "Tag driver for Ocelot family of switches, using VLAN"
-	depends on MSCC_OCELOT_SWITCH_LIB || \
-	          (MSCC_OCELOT_SWITCH_LIB=n && COMPILE_TEST)
 	help
 	  Say Y or M if you want to enable support for tagging frames with a
 	  custom VLAN-based header. Frames that require timestamping, such as
diff --git a/net/dsa/tag_ocelot_8021q.c b/net/dsa/tag_ocelot_8021q.c
index 1e4e66ea6796..d05c352f96e5 100644
--- a/net/dsa/tag_ocelot_8021q.c
+++ b/net/dsa/tag_ocelot_8021q.c
@@ -10,10 +10,31 @@
  */
 #include <linux/dsa/8021q.h>
 #include <linux/dsa/ocelot.h>
-#include <soc/mscc/ocelot.h>
-#include <soc/mscc/ocelot_ptp.h>
 #include "dsa_priv.h"
 
+static struct sk_buff *ocelot_defer_xmit(struct dsa_port *dp,
+					 struct sk_buff *skb)
+{
+	struct felix_deferred_xmit_work *xmit_work;
+	struct felix_port *felix_port = dp->priv;
+
+	xmit_work = kzalloc(sizeof(*xmit_work), GFP_ATOMIC);
+	if (!xmit_work)
+		return NULL;
+
+	/* Calls felix_port_deferred_xmit in felix.c */
+	kthread_init_work(&xmit_work->work, felix_port->xmit_work_fn);
+	/* Increase refcount so the kfree_skb in dsa_slave_xmit
+	 * won't really free the packet.
+	 */
+	xmit_work->dp = dp;
+	xmit_work->skb = skb_get(skb);
+
+	kthread_queue_work(felix_port->xmit_worker, &xmit_work->work);
+
+	return NULL;
+}
+
 static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
 				   struct net_device *netdev)
 {
@@ -21,18 +42,9 @@ static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
 	u16 tx_vid = dsa_8021q_tx_vid(dp->ds, dp->index);
 	u16 queue_mapping = skb_get_queue_mapping(skb);
 	u8 pcp = netdev_txq_to_tc(netdev, queue_mapping);
-	struct ocelot *ocelot = dp->ds->priv;
-	int port = dp->index;
-	u32 rew_op = 0;
 
-	rew_op = ocelot_ptp_rew_op(skb);
-	if (rew_op) {
-		if (!ocelot_can_inject(ocelot, 0))
-			return NULL;
-
-		ocelot_port_inject_frame(ocelot, port, 0, rew_op, skb);
-		return NULL;
-	}
+	if (ocelot_ptp_rew_op(skb))
+		return ocelot_defer_xmit(dp, skb);
 
 	return dsa_8021q_xmit(skb, netdev, ETH_P_8021Q,
 			      ((pcp << VLAN_PRIO_SHIFT) | tx_vid));