> -----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.
>
> > +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).
