net: dsa: free skb->cb usage in core driver

Free skb->cb usage in core driver and let device drivers decide to
use or not. The reason having a DSA_SKB_CB(skb)->clone was because
dsa_skb_tx_timestamp() which may set the clone pointer was called
before p->xmit() which would use the clone if any, and the device
driver has no way to initialize the clone pointer.

This patch just put memset(skb->cb, 0, sizeof(skb->cb)) at beginning
of dsa_slave_xmit(). Some new features in the future, like one-step
timestamp may need more bytes of skb->cb to use in
dsa_skb_tx_timestamp(), and p->xmit().
Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/ocelot/felix.c

@@ -1408,7 +1408,7 @@ static void felix_txtstamp(struct dsa_switch *ds, int port,
 			return;
 
 		ocelot_port_add_txtstamp_skb(ocelot, port, clone);
-		DSA_SKB_CB(skb)->clone = clone;
+		OCELOT_SKB_CB(skb)->clone = clone;
 	}
 }
 

drivers/net/dsa/sja1105/sja1105_main.c

@@ -3137,7 +3137,7 @@ static void sja1105_port_deferred_xmit(struct kthread_work *work)
 	struct sk_buff *skb;
 
 	while ((skb = skb_dequeue(&sp->xmit_queue)) != NULL) {
-		struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
+		struct sk_buff *clone = SJA1105_SKB_CB(skb)->clone;
 
 		mutex_lock(&priv->mgmt_lock);
 

drivers/net/dsa/sja1105/sja1105_ptp.c

@@ -432,7 +432,7 @@ bool sja1105_port_rxtstamp(struct dsa_switch *ds, int port,
 }
 
 /* Called from dsa_skb_tx_timestamp. This callback is just to clone
- * the skb and have it available in DSA_SKB_CB in the .port_deferred_xmit
+ * the skb and have it available in SJA1105_SKB_CB in the .port_deferred_xmit
  * callback, where we will timestamp it synchronously.
  */
 void sja1105_port_txtstamp(struct dsa_switch *ds, int port, struct sk_buff *skb)
@@ -448,7 +448,7 @@ void sja1105_port_txtstamp(struct dsa_switch *ds, int port, struct sk_buff *skb)
 	if (!clone)
 		return;
 
-	DSA_SKB_CB(skb)->clone = clone;
+	SJA1105_SKB_CB(skb)->clone = clone;
 }
 
 static int sja1105_ptp_reset(struct dsa_switch *ds)

drivers/net/ethernet/mscc/ocelot.c

@@ -538,8 +538,8 @@ void ocelot_port_add_txtstamp_skb(struct ocelot *ocelot, int port,
 	spin_lock(&ocelot_port->ts_id_lock);
 
 	skb_shinfo(clone)->tx_flags |= SKBTX_IN_PROGRESS;
-	/* Store timestamp ID in cb[0] of sk_buff */
-	clone->cb[0] = ocelot_port->ts_id;
+	/* Store timestamp ID in OCELOT_SKB_CB(clone)->ts_id */
+	OCELOT_SKB_CB(clone)->ts_id = ocelot_port->ts_id;
 	ocelot_port->ts_id = (ocelot_port->ts_id + 1) % 4;
 	skb_queue_tail(&ocelot_port->tx_skbs, clone);
 
@@ -604,7 +604,7 @@ void ocelot_get_txtstamp(struct ocelot *ocelot)
 		spin_lock_irqsave(&port->tx_skbs.lock, flags);
 
 		skb_queue_walk_safe(&port->tx_skbs, skb, skb_tmp) {
-			if (skb->cb[0] != id)
+			if (OCELOT_SKB_CB(skb)->ts_id != id)
 				continue;
 			__skb_unlink(skb, &port->tx_skbs);
 			skb_match = skb;

drivers/net/ethernet/mscc/ocelot_net.c

@@ -520,7 +520,7 @@ static netdev_tx_t ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
 
 			ocelot_port_add_txtstamp_skb(ocelot, port, clone);
 
-			rew_op |= clone->cb[0] << 3;
+			rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
 		}
 	}
 

include/linux/dsa/sja1105.h

@@ -47,11 +47,12 @@ struct sja1105_tagger_data {
 };
 
 struct sja1105_skb_cb {
+	struct sk_buff *clone;
 	u32 meta_tstamp;
 };
 
 #define SJA1105_SKB_CB(skb) \
-	((struct sja1105_skb_cb *)DSA_SKB_CB_PRIV(skb))
+	((struct sja1105_skb_cb *)((skb)->cb))
 
 struct sja1105_port {
 	u16 subvlan_map[DSA_8021Q_N_SUBVLAN];

include/net/dsa.h

@@ -117,20 +117,6 @@ struct dsa_netdevice_ops {
 #define MODULE_ALIAS_DSA_TAG_DRIVER(__proto)				\
 	MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS __stringify(__proto##_VALUE))
 
-struct dsa_skb_cb {
-	struct sk_buff *clone;
-};
-
-struct __dsa_skb_cb {
-	struct dsa_skb_cb cb;
-	u8 priv[48 - sizeof(struct dsa_skb_cb)];
-};
-
-#define DSA_SKB_CB(skb) ((struct dsa_skb_cb *)((skb)->cb))
-
-#define DSA_SKB_CB_PRIV(skb)			\
-	((void *)(skb)->cb + offsetof(struct __dsa_skb_cb, priv))
-
 struct dsa_switch_tree {
 	struct list_head	list;
 

include/soc/mscc/ocelot.h

@@ -689,6 +689,14 @@ struct ocelot_policer {
 	u32 burst; /* bytes */
 };
 
+struct ocelot_skb_cb {
+	struct sk_buff *clone;
+	u8 ts_id;
+};
+
+#define OCELOT_SKB_CB(skb) \
+	((struct ocelot_skb_cb *)((skb)->cb))
+
 #define ocelot_read_ix(ocelot, reg, gi, ri) __ocelot_read_ix(ocelot, reg, reg##_GSZ * (gi) + reg##_RSZ * (ri))
 #define ocelot_read_gix(ocelot, reg, gi) __ocelot_read_ix(ocelot, reg, reg##_GSZ * (gi))
 #define ocelot_read_rix(ocelot, reg, ri) __ocelot_read_ix(ocelot, reg, reg##_RSZ * (ri))

net/dsa/slave.c

@@ -614,7 +614,7 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	dev_sw_netstats_tx_add(dev, 1, skb->len);
 
-	DSA_SKB_CB(skb)->clone = NULL;
+	memset(skb->cb, 0, sizeof(skb->cb));
 
 	/* Handle tx timestamp if any */
 	dsa_skb_tx_timestamp(p, skb);

net/dsa/tag_ocelot.c

@@ -15,11 +15,11 @@ static void ocelot_xmit_ptp(struct dsa_port *dp, void *injection,
 	ocelot_port = ocelot->ports[dp->index];
 	rew_op = ocelot_port->ptp_cmd;
 
-	/* Retrieve timestamp ID populated inside skb->cb[0] of the
-	 * clone by ocelot_port_add_txtstamp_skb
+	/* Retrieve timestamp ID populated inside OCELOT_SKB_CB(clone)->ts_id
+	 * by ocelot_port_add_txtstamp_skb
 	 */
 	if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
-		rew_op |= clone->cb[0] << 3;
+		rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
 
 	ocelot_ifh_set_rew_op(injection, rew_op);
 }
@@ -28,7 +28,7 @@ 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 sk_buff *clone = OCELOT_SKB_CB(skb)->clone;
 	struct dsa_switch *ds = dp->ds;
 	void *injection;
 	__be32 *prefix;

net/dsa/tag_ocelot_8021q.c

@@ -28,11 +28,11 @@ static struct sk_buff *ocelot_xmit_ptp(struct dsa_port *dp,
 	ocelot_port = ocelot->ports[port];
 	rew_op = ocelot_port->ptp_cmd;
 
-	/* Retrieve timestamp ID populated inside skb->cb[0] of the
-	 * clone by ocelot_port_add_txtstamp_skb
+	/* Retrieve timestamp ID populated inside OCELOT_SKB_CB(clone)->ts_id
+	 * by ocelot_port_add_txtstamp_skb
 	 */
 	if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
-		rew_op |= clone->cb[0] << 3;
+		rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
 
 	ocelot_port_inject_frame(ocelot, port, 0, rew_op, skb);
 
@@ -46,7 +46,7 @@ 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 sk_buff *clone = DSA_SKB_CB(skb)->clone;
+	struct sk_buff *clone = OCELOT_SKB_CB(skb)->clone;
 
 	/* TX timestamping was requested, so inject through MMIO */
 	if (clone)