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

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Message-ID: <87pn8zncqo.fsf@kurt>
Date:   Mon, 13 Jul 2020 08:35:43 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org, Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH v1 4/8] net: dsa: hellcreek: Add support for hardware timestamping

On Sat Jul 11 2020, Richard Cochran wrote:
> 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!

Indeed. Never thought about it.

Thanks,
Kurt

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