netdev - Re: [PATCH 1/3] net: macb: Fix PTP one step sync support

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Date:   Wed, 18 May 2022 09:53:29 +0530
From:   Harini Katakam <harinik@...inx.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Harini Katakam <harini.katakam@...inx.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        David Miller <davem@...emloft.net>,
        Richard Cochran <richardcochran@...il.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
Subject: Re: [PATCH 1/3] net: macb: Fix PTP one step sync support

Hi Jakub,

On Wed, May 18, 2022 at 8:12 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 17 May 2022 13:02:57 +0530 Harini Katakam wrote:
> > PTP one step sync packets cannot have CSUM padding and insertion in
> > SW since time stamp is inserted on the fly by HW.
> > In addition, ptp4l version 3.0 and above report an error when skb
> > timestamps are reported for packets that not processed for TX TS
> > after transmission.
> > Add a helper to identify PTP one step sync and fix the above two
> > errors.
> > Also reset ptp OSS bit when one step is not selected.
> >
> > Fixes: ab91f0a9b5f4 ("net: macb: Add hardware PTP support")
> > Fixes: 653e92a9175e ("net: macb: add support for padding and fcs computation")
>
> Please make sure to CC authors of the patches under fixes.
> ./scripts/get_maintainer should point them out.

Thanks for the review.
Rafal Ozieblo <rafalo@...ence.com> is the author of the first Fixes
patch but that
address hasn't worked in the last ~4 yrs.
I have cced Claudiu and everyone else from the maintainers
(Eric Dumazet <edumazet@...gle.com> also doesn't work)

<snip>
> > +/* IEEE1588 PTP flag field values  */
> > +#define PTP_FLAG_TWOSTEP     0x2
>
> Shouldn't this go into the PTP header?

Let me add it to ptp_classify where the relevant helpers are present.

<snip>
> > +static inline bool ptp_oss(struct sk_buff *skb)
>
> Please spell out then name more oss == open source software.

Will change to ptp_one_step_sync

>
> No inline here, please, let the compiler decide if the function is
> small enough. One step timestamp may be a rare use case so inlining
> this twice is not necessarily the right choice.

One step is a rare case but the check happens on every PTP packet in the
transmit data path and hence I wanted to explicitly inline it.

<snip>
> > @@ -1158,13 +1192,14 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
> >
> >                       /* First, update TX stats if needed */
> >                       if (skb) {
> > -                             if (unlikely(skb_shinfo(skb)->tx_flags &
> > -                                          SKBTX_HW_TSTAMP) &&
> > -                                 gem_ptp_do_txstamp(queue, skb, desc) == 0) {
> > -                                     /* skb now belongs to timestamp buffer
> > -                                      * and will be removed later
> > -                                      */
> > -                                     tx_skb->skb = NULL;
> > +                             if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) &&
>
> ptp_oss already checks if HW_TSTAMP is set.

The check for SKBTX_HW_TSTAMP is required here universally and not
just inside ptp_oss.
I will remove the redundant check in ptp_oss instead. Please see the
reply below.

>
> > +                                 !ptp_oss(skb)) {
> > +                                     if (gem_ptp_do_txstamp(queue, skb, desc) == 0) {
>
> Why convert the gem_ptp_do_txstamp check from a && in the condition to
> a separate if?

The intention is that ptp_oss should only be evaluated when
SKBTX_HW_TSTAMP is set and
gem_ptp_do_txstamp should only be called if ptp_oss is false. Since
compiler follows the order
of evaluation, I'll simplify this to:

if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) && !ptp_oss(skb) &&
    gem_ptp_do_txstamp(queue, skb, desc) == 0) {
...
}

Regards,
Harini