netdev - Re: [PATCH net-next 09/12] ionic: add and enable tx and rx timestamp handling

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Date:   Mon, 5 Apr 2021 11:20:42 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Shannon Nelson <snelson@...sando.io>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        drivers@...sando.io, Allen Hubbe <allenbh@...sando.io>
Subject: Re: [PATCH net-next 09/12] ionic: add and enable tx and rx timestamp
 handling

On Mon, Apr 05, 2021 at 09:28:44AM -0700, Shannon Nelson wrote:
> On 4/4/21 4:41 PM, Richard Cochran wrote:
> > On Thu, Apr 01, 2021 at 10:56:07AM -0700, Shannon Nelson wrote:
> > 
> > > @@ -1150,6 +1232,10 @@ netdev_tx_t ionic_start_xmit(struct sk_buff *skb, struct net_device *netdev)
> > >   		return NETDEV_TX_OK;
> > >   	}
> > > +	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))
> > > +		if (lif->hwstamp_txq)
> > > +			return ionic_start_hwstamp_xmit(skb, netdev);
> > The check for SKBTX_HW_TSTAMP and hwstamp_txq is good, but I didn't
> > see hwstamp_txq getting cleared in ionic_lif_hwstamp_set() when the
> > user turns off Tx time stamping via the SIOCSHWTSTAMP ioctl.
> 
> Once the hwstamp queues are up, we leave them there for future use until the
> interface is stopped,

Fine, but

> assuming that the stack isn't going to send us
> SKBTX_HW_STAMP after it has disabled the offload.

you can't assume that.  This is an important point, especially
considering the possibiliy of stacked HW time stamp providers.  I'm
working on a patch set that will allow the user to switch between MAC
and PHY time stamping at run time.

Thanks,
Richard