-----Original Message-----
From: Rafal Ozieblo 
Sent: 28 grudnia 2016 14:23
Subject: RE: [RFC PATCH net-next v4 1/2] macb: Add 1588 support in Cadence GEM.

quoted

+static void gem_ptp_tx_hwtstamp(struct macb *bp, struct sk_buff *skb,
+				int peer_ev)
+{
+	struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
+	struct timespec64 ts;
+	u64 ns;
+
+	/* PTP Peer Event Frame packets */
+	if (peer_ev) {
+		ts.tv_sec = gem_readl(bp, PEFTSL);
+		ts.tv_nsec = gem_readl(bp, PEFTN);
+
+	/* PTP Event Frame packets */
+	} else {
+		ts.tv_sec = gem_readl(bp, EFTSL);
+		ts.tv_nsec = gem_readl(bp, EFTN);
+	}

I'm wondering what is a difference between timestamp in transmit buffer descriptor (Word 2 and 3) and PTP Event Frame Transmitted Seconds/Nanoseconds Register (0x1E0, 0x1E4).

According Cadence Hardware team:
"It is just that some customers prefer to have the time in the descriptors as that is provided per frame.
The registers are simply overwritten when a new event frame is transmitted/received and so software could miss it."
The question is are you sure that you read timestamp for current frame? (not for the next frame).