[PATCH 5.7 41/79] net: mscc: ocelot: fix hardware timestamp dequeue logic

[Greg Kroah-Hartman]

From: laurent brando <laurent.brando@xxxxxxx>

[ 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 <laurent.brando@xxxxxxx>
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Signed-off-by: Yangbo Lu <yangbo.lu@xxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 efb3965a3e42b..76dbf9ac8ad50 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);
-- 
2.25.1