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Date:   Tue, 12 Mar 2019 21:37:14 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Paul Thomas <pthomas8589@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH] Check for SKBTX_HW_TSTAMP in macb driver



> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
> Behalf Of Paul Thomas
> Sent: Tuesday, March 12, 2019 1:05 PM
> To: netdev@...r.kernel.org
> Subject: Re: [PATCH] Check for SKBTX_HW_TSTAMP in macb driver
> 
> On Tue, Mar 12, 2019 at 3:51 PM Paul Thomas <pthomas8589@...il.com> wrote:
> >
> > Make sure SKBTX_HW_TSTAMP (i.e. SOF_TIMESTAMPING_TX_HARDWARE) has
> been enabled for this skb
> > This is a concept for discussion, more testing is needed.
> > It does fix the issue where normal socks that aren't expecting a timestamp will not
> wake
> > up on select.
> > ---
> >  drivers/net/ethernet/cadence/macb_main.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/cadence/macb_main.c
> b/drivers/net/ethernet/cadence/macb_main.c
> > index ad099fd01b45..b2f184fc1370 100644
> > --- a/drivers/net/ethernet/cadence/macb_main.c
> > +++ b/drivers/net/ethernet/cadence/macb_main.c
> > @@ -898,11 +898,13 @@ static void macb_tx_interrupt(struct macb_queue
> *queue)
> >
> >                         /* First, update TX stats if needed */
> >                         if (skb) {
> > -                               if (gem_ptp_do_txstamp(queue, skb, desc) == 0) {
> > -                                       /* skb now belongs to timestamp buffer
> > -                                        * and will be removed later
> > -                                        */
> I think the above does the same thing as if CONFIG_MACB_USE_HWSTAMP is
> undefined regarding cleanup, so there is no extra cleanup if the
> gem_ptp_do_txstamp() path isn't taken, but I wasn't sure about the
> "skb now belongs to the timestamp buffer" if we don't go down that
> path.

The path they're taking here seems a bit weird... I suspect the function gem_ptp_do_txstamp is doing something.

Normally the driver should use something like skb_get to obtain a reference to the skb.

However, the main goal of this patch is correct.

Thanks,
Jake

> > -                                       tx_skb->skb = NULL;
> > +                               if(unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)) {
> This looks like how other drivers are doing things
> > +                                       if (gem_ptp_do_txstamp(queue, skb, desc) == 0) {
> > +                                               /* skb now belongs to timestamp buffer
> > +                                                * and will be removed later
> > +                                                */
> > +                                               tx_skb->skb = NULL;
> > +                                       }
> >                                 }
> >                                 netdev_vdbg(bp->dev, "skb %u (data %p) TX complete\n",
> >                                             macb_tx_ring_wrap(bp, tail),
> > --
> > 2.17.1
> >

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