net: dsa: check tx timestamp request in core driver

Check tx timestamp request in core driver at very beginning of
dsa_skb_tx_timestamp(), so that most skbs not requiring tx
timestamp just return. And drop such checking in device drivers.
Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Tested-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/hirschmann/hellcreek_hwtstamp.c

@@ -382,10 +382,6 @@ bool hellcreek_port_txtstamp(struct dsa_switch *ds, int port,
 
 	ps = &hellcreek->ports[port].port_hwtstamp;
 
-	/* Check if the driver is expected to do HW timestamping */
-	if (!(skb_shinfo(clone)->tx_flags & SKBTX_HW_TSTAMP))
-		return false;
-
 	/* Make sure the message is a PTP message that needs to be timestamped
 	 * and the interaction with the HW timestamping is enabled. If not, stop
 	 * here

drivers/net/dsa/mv88e6xxx/hwtstamp.c

@@ -475,9 +475,6 @@ bool mv88e6xxx_port_txtstamp(struct dsa_switch *ds, int port,
 	struct mv88e6xxx_port_hwtstamp *ps = &chip->port_hwtstamp[port];
 	struct ptp_header *hdr;
 
-	if (!(skb_shinfo(clone)->tx_flags & SKBTX_HW_TSTAMP))
-		return false;
-
 	hdr = mv88e6xxx_should_tstamp(chip, port, clone, type);
 	if (!hdr)
 		return false;

drivers/net/dsa/ocelot/felix.c

@@ -1401,8 +1401,7 @@ static bool felix_txtstamp(struct dsa_switch *ds, int port,
 	struct ocelot *ocelot = ds->priv;
 	struct ocelot_port *ocelot_port = ocelot->ports[port];
 
-	if (ocelot->ptp && (skb_shinfo(clone)->tx_flags & SKBTX_HW_TSTAMP) &&
-	    ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
+	if (ocelot->ptp && ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
 		ocelot_port_add_txtstamp_skb(ocelot, port, clone);
 		return true;
 	}

net/dsa/slave.c

@@ -559,6 +559,9 @@ static void dsa_skb_tx_timestamp(struct dsa_slave_priv *p,
 	struct sk_buff *clone;
 	unsigned int type;
 
+	if (!(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))
+		return;
+
 	type = ptp_classify_raw(skb);
 	if (type == PTP_CLASS_NONE)
 		return;