netdev - [PATCH] net: mscc: ocelot: fix hardware timestamp dequeue logic

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Date:   Mon, 27 Jul 2020 18:26:14 +0800
From:   Yangbo Lu <yangbo.lu@....com>
To:     netdev@...r.kernel.org
Cc:     Yangbo Lu <yangbo.lu@....com>,
        laurent brando <laurent.brando@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>
Subject: [PATCH] net: mscc: ocelot: fix hardware timestamp dequeue logic

From: laurent brando <laurent.brando@....com>

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@....com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
Signed-off-by: Yangbo Lu <yangbo.lu@....com>
---
 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 e05a48c..82bde07 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -731,21 +731,21 @@ 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);
-- 
2.7.4