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

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Date:   Sat, 11 Jul 2020 13:38:10 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
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 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@...il.com>