Re: [PATCH v1 4/8] net: dsa: hellcreek: Add support for hardware timestamping

On Fri, Jul 10, 2020 at 01:36:07PM +0200, Kurt Kanzenbach wrote:

+static void hellcreek_get_rxts(struct hellcreek *hellcreek,
+			       struct hellcreek_port_hwtstamp *ps,
+			       struct sk_buff *skb, struct sk_buff_head *rxq,
+			       int port)
+{
+	struct skb_shared_hwtstamps *shwt;
+	struct sk_buff_head received;
+	unsigned long flags;
+
+	/* The latched timestamp belongs to one of the received frames. */
+	__skb_queue_head_init(&received);
+
+	/* Lock & disable interrupts */
+	spin_lock_irqsave(&rxq->lock, flags);
+
+	/* Add the reception queue "rxq" to the "received" queue an reintialize
+	 * "rxq".  From now on, we deal with "received" not with "rxq"
+	 */
+	skb_queue_splice_tail_init(rxq, &received);
+
+	spin_unlock_irqrestore(&rxq->lock, flags);
+
+	for (; skb; skb = __skb_dequeue(&received)) {
+		unsigned int type;
+		u8 *hdr;
+		u64 ns;
+
+		/* Get nanoseconds from ptp packet */
+		type = SKB_PTP_TYPE(skb);
+		hdr  = parse_ptp_header(skb, type);
+		ns   = hellcreek_get_reserved_field(hdr);

You might consider clearing the reserved field at this point.  Some
user space SW might consider non-zero reserved fields as corrupt!

(The LinuxPTP stack doesn't do this, but still maybe others are more
pedantic.)


Acked-by: Richard Cochran <richardcochran@gmail.com>