netdev - RE: [PATCH] Check for SKBTX_HW

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Date:   Wed, 13 Mar 2019 14:50:31 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Harini Katakam <harinik@...inx.com>
CC:     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: Harini Katakam [mailto:harinik@...inx.com]
> Sent: Tuesday, March 12, 2019 11:00 PM
> To: Keller, Jacob E <jacob.e.keller@...el.com>
> Cc: Paul Thomas <pthomas8589@...il.com>; netdev@...r.kernel.org
> Subject: Re: [PATCH] Check for SKBTX_HW_TSTAMP in macb driver
> 
> Hi Paul, Jake,
> On Wed, Mar 13, 2019 at 3:08 AM Keller, Jacob E
> <jacob.e.keller@...el.com> wrote:
> >
> >
> >
> > > -----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:
> > > >
> <snip>
> > > >                         /* 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.
> 
> Just FYI, this is the historical reason for the skb implementation here:
> https://patchwork.kernel.org/patch/9473937/
> 
> Regards,
> Harini

I'm not sure I follow that logic, but I obviously haven't dug into what gem_ptp_do_txstamp does, or what calls its making.

Either way, I think this patch is a strict improvement on what was previously happening. It can be someone else's responsibility to change how the skb is handled if they find an issue with it.

Thanks,
Jake