net: stmmac: set IC bit when transmitting frames with HW timestamp

When transmitting certain PTP frames, e.g. SYNC and DELAY_REQ, the
PTP daemon, e.g. ptp4l, is polling the driver for the frame transmit
hardware timestamp. The polling will most likely timeout if the tx
coalesce is enabled due to the Interrupt-on-Completion (IC) bit is
not set in tx descriptor for those frames.

This patch will ignore the tx coalesce parameter and set the IC bit
when transmitting PTP frames which need to report out the frame
transmit hardware timestamp to user space.

Fixes: f748be53 ("net: stmmac: Rework coalesce timer and fix multi-queue races")
Signed-off-by: Roland Hii <roland.king.guan.hii@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -2947,12 +2947,15 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	/* Manage tx mitigation */
 	tx_q->tx_count_frames += nfrags + 1;
-	if (priv->tx_coal_frames <= tx_q->tx_count_frames) {
+	if (likely(priv->tx_coal_frames > tx_q->tx_count_frames) &&
+	    !(priv->synopsys_id >= DWMAC_CORE_4_00 &&
+	    (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
+	    priv->hwts_tx_en)) {
+		stmmac_tx_timer_arm(priv, queue);
+	} else {
+		tx_q->tx_count_frames = 0;
 		stmmac_set_tx_ic(priv, desc);
 		priv->xstats.tx_set_ic_bit++;
-		tx_q->tx_count_frames = 0;
-	} else {
-		stmmac_tx_timer_arm(priv, queue);
 	}
 
 	skb_tx_timestamp(skb);
@@ -3166,12 +3169,15 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	 * element in case of no SG.
 	 */
 	tx_q->tx_count_frames += nfrags + 1;
-	if (priv->tx_coal_frames <= tx_q->tx_count_frames) {
+	if (likely(priv->tx_coal_frames > tx_q->tx_count_frames) &&
+	    !(priv->synopsys_id >= DWMAC_CORE_4_00 &&
+	    (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
+	    priv->hwts_tx_en)) {
+		stmmac_tx_timer_arm(priv, queue);
+	} else {
+		tx_q->tx_count_frames = 0;
 		stmmac_set_tx_ic(priv, desc);
 		priv->xstats.tx_set_ic_bit++;
-		tx_q->tx_count_frames = 0;
-	} else {
-		stmmac_tx_timer_arm(priv, queue);
 	}
 
 	skb_tx_timestamp(skb);