Subject: [PATCH 05/26] net: mscc: ocelot: fix hardware timestamp dequeue logic

From: laurent brando <[email-masked]>
Date: Mon, 27 Jul 2020 18:26:14 +0800

[ Upstream commit 5fd82200d870a5dd3e509c98ef2041f580b2c0e1 ]

The next hw timestamp should be snapshoot to the read registers
only once the current timestamp has been read.
If none of the pending skbs matches the current HW timestamp
just gracefully flush the available timestamp by reading it.

Signed-off-by: laurent brando <[email-masked]>
Signed-off-by: Vladimir Oltean <[email-masked]>
Signed-off-by: Yangbo Lu <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 drivers/net/ethernet/mscc/ocelot.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index efb3965a3e42..76dbf9ac8ad5 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -749,21 +749,21 @@ void ocelot_get_txtstamp(struct ocelot *ocelot)
 
 		spin_unlock_irqrestore(&port->tx_skbs.lock, flags);
 
-		/* Next ts */
-		ocelot_write(ocelot, SYS_PTP_NXT_PTP_NXT, SYS_PTP_NXT);
+		/* Get the h/w timestamp */
+		ocelot_get_hwtimestamp(ocelot, &ts);
 
 		if (unlikely(!skb_match))
 			continue;
 
-		/* Get the h/w timestamp */
-		ocelot_get_hwtimestamp(ocelot, &ts);
-
 		/* Set the timestamp into the skb */
 		memset(&shhwtstamps, 0, sizeof(shhwtstamps));
 		shhwtstamps.hwtstamp = ktime_set(ts.tv_sec, ts.tv_nsec);
 		skb_tstamp_tx(skb_match, &shhwtstamps);
 
 		dev_kfree_skb_any(skb_match);
+
+		/* Next ts */
+		ocelot_write(ocelot, SYS_PTP_NXT_PTP_NXT, SYS_PTP_NXT);
 	}
 }
 EXPORT_SYMBOL(ocelot_get_txtstamp);
-- 
2.26.2