netdev - RE: [RFC PATCH net-next v4 1/2] macb: Add 1588 support in Cadence GEM.

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Date:   Mon, 2 Jan 2017 09:36:10 +0000
From:   Rafal Ozieblo <rafalo@...ence.com>
To:     Andrei Pistirica <andrei.pistirica@...rochip.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "nicolas.ferre@...el.com" <nicolas.ferre@...el.com>,
        "harinikatakamlinux@...il.com" <harinikatakamlinux@...il.com>,
        "harini.katakam@...inx.com" <harini.katakam@...inx.com>
CC:     "punnaia@...inx.com" <punnaia@...inx.com>,
        "michals@...inx.com" <michals@...inx.com>,
        "anirudh@...inx.com" <anirudh@...inx.com>,
        "boris.brezillon@...e-electrons.com" 
        <boris.brezillon@...e-electrons.com>,
        "alexandre.belloni@...e-electrons.com" 
        <alexandre.belloni@...e-electrons.com>,
        "tbultel@...elsurmer.com" <tbultel@...elsurmer.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>
Subject: RE: [RFC PATCH net-next v4 1/2] macb: Add 1588 support in Cadence
 GEM.

> -----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).