netdev - Re: [PATCH] Check for SKBTX_HW

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Date:   Tue, 12 Mar 2019 16:05:11 -0400
From:   Paul Thomas <pthomas8589@...il.com>
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.
> -                                       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
>