[PATCH v2 net 2/8] net: mscc: ocelot: add locking for the port TX timestamp ID

[Vladimir Oltean <olteanv@gmail.com>]

From: Vladimir Oltean <vladimir.oltean@nxp.com>

The ocelot_port->ts_id is used to:
(a) populate skb->cb[0] for matching the TX timestamp in the PTP IRQ
    with an skb.
(b) populate the REW_OP from the injection header of the ongoing skb.
Only then is ocelot_port->ts_id incremented.

This is a problem because, at least theoretically, another timestampable
skb might use the same ocelot_port->ts_id before that is incremented.
Normally all transmit calls are serialized by the netdev transmit
spinlock, but in this case, ocelot_port_add_txtstamp_skb() is also
called by DSA, which has started declaring the NETIF_F_LLTX feature
since commit 2b86cb829976 ("net: dsa: declare lockless TX feature for
slave ports").  So the logic of using and incrementing the timestamp id
should be atomic per port.

The solution is to use the global ocelot_port->ts_id only while
protected by the associated ocelot_port->ts_id_lock. That's where we
populate skb->cb[0]. Note that for ocelot, ocelot_port_add_txtstamp_skb
is called for the actual skb, but for felix, it is called for the skb's
clone. That is something which will also be changed in the future.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
---
Changes in v2:
Added an extra explanation about NETIF_F_LLTX in commit message.

 drivers/net/ethernet/mscc/ocelot.c     |  8 +++++++-
 drivers/net/ethernet/mscc/ocelot_net.c |  6 ++----
 include/soc/mscc/ocelot.h              |  1 +
 net/dsa/tag_ocelot.c                   | 11 +++++++----
 4 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 5abb7d2b0a9e..83eb7c325061 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -421,10 +421,15 @@ int ocelot_port_add_txtstamp_skb(struct ocelot_port *ocelot_port,
 
 	if (ocelot->ptp && shinfo->tx_flags & SKBTX_HW_TSTAMP &&
 	    ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
+		spin_lock(&ocelot_port->ts_id_lock);
+
 		shinfo->tx_flags |= SKBTX_IN_PROGRESS;
 		/* Store timestamp ID in cb[0] of sk_buff */
-		skb->cb[0] = ocelot_port->ts_id % 4;
+		skb->cb[0] = ocelot_port->ts_id;
+		ocelot_port->ts_id = (ocelot_port->ts_id + 1) % 4;
 		skb_queue_tail(&ocelot_port->tx_skbs, skb);
+
+		spin_unlock(&ocelot_port->ts_id_lock);
 		return 0;
 	}
 	return -ENODATA;
@@ -1300,6 +1305,7 @@ void ocelot_init_port(struct ocelot *ocelot, int port)
 	struct ocelot_port *ocelot_port = ocelot->ports[port];
 
 	skb_queue_head_init(&ocelot_port->tx_skbs);
+	spin_lock_init(&ocelot_port->ts_id_lock);
 
 	/* Basic L2 initialization */
 
diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
index cacabc23215a..8490e42e9e2d 100644
--- a/drivers/net/ethernet/mscc/ocelot_net.c
+++ b/drivers/net/ethernet/mscc/ocelot_net.c
@@ -349,10 +349,8 @@ static int ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	if (ocelot->ptp && shinfo->tx_flags & SKBTX_HW_TSTAMP) {
 		info.rew_op = ocelot_port->ptp_cmd;
-		if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
-			info.rew_op |= (ocelot_port->ts_id  % 4) << 3;
-			ocelot_port->ts_id++;
-		}
+		if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
+			info.rew_op |= skb->cb[0] << 3;
 	}
 
 	ocelot_gen_ifh(ifh, &info);
diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
index da369b12005f..4521dd602ddc 100644
--- a/include/soc/mscc/ocelot.h
+++ b/include/soc/mscc/ocelot.h
@@ -566,6 +566,7 @@ struct ocelot_port {
 	u8				ptp_cmd;
 	struct sk_buff_head		tx_skbs;
 	u8				ts_id;
+	spinlock_t			ts_id_lock;
 
 	phy_interface_t			phy_mode;
 
diff --git a/net/dsa/tag_ocelot.c b/net/dsa/tag_ocelot.c
index 42f327c06dca..b4fc05cafaa6 100644
--- a/net/dsa/tag_ocelot.c
+++ b/net/dsa/tag_ocelot.c
@@ -160,11 +160,14 @@ static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
 	packing(injection, &qos_class, 19,  17, OCELOT_TAG_LEN, PACK, 0);
 
 	if (ocelot->ptp && (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)) {
+		struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
+
 		rew_op = ocelot_port->ptp_cmd;
-		if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
-			rew_op |= (ocelot_port->ts_id  % 4) << 3;
-			ocelot_port->ts_id++;
-		}
+		/* Retrieve timestamp ID populated inside skb->cb[0] of the
+		 * clone by ocelot_port_add_txtstamp_skb
+		 */
+		if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
+			rew_op |= clone->cb[0] << 3;
 
 		packing(injection, &rew_op, 125, 117, OCELOT_TAG_LEN, PACK, 0);
 	}
-- 
2.25.1