Re: [Intel-wired-lan] [PATCH net] igc: Fix RX HW timestamp reporting when NET_RX_BUSY_POLL is disabled

[Ding Meng]

Dear Paul,

Thanks for your comments.

On Mon, Jun 22, 2026 at 05:59:53PM +0200, Paul Menzel wrote: 
> Am 22.06.26 um 06:13 schrieb Ding Meng via Intel-wired-lan:
> > When CONFIG_NET_RX_BUSY_POLL is deactivated, fetching RX HW timestamps
> > from the NIC no longer works as expected.
> 
> Maybe paste some logs/errors, so it can be easier found by people with the
> same issue.

Will do.
 
> > This occurs because disabling CONFIG_NET_RX_BUSY_POLL disables the
> > SKB NAPI mapping in __skb_mark_napi_id(). Consequently, get_timestamp()
> > fails to perform its driver lookup, and the igc driver's struct
> > net_device_ops::ndo_get_tstamp is never invoked.
> > 
> > Instead, get_timestamp() falls back to use shhwtstamps(skb)->hwtstamp,
> > a field that the driver has not populated.
> > 
> > Fix this by populating the hwtstamp field with the correct timestamp
> > in the default timer when CONFIG_NET_RX_BUSY_POLL is disabled.
> 
> Maybe detail, why the adapter needs to be passed now.
> 
> Also, please describe a test case to check the change.

Will do.

> > diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> > index 8ac16808023..1da8d7aa76d 100644
> > --- a/drivers/net/ethernet/intel/igc/igc_main.c
> > +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> > @@ -1992,7 +1992,26 @@ static struct sk_buff *igc_build_skb(struct igc_ring *rx_ring,
> >   	return skb;
> >   }
> > -static struct sk_buff *igc_construct_skb(struct igc_ring *rx_ring,
> > +static void igc_construct_skb_timestamps(struct igc_adapter *adapter,
> > +					 struct sk_buff *skb,
> > +					 struct igc_xdp_buff *ctx)
> > +{
> > +	if (!ctx->rx_ts)
> > +		return;
> > +#ifdef CONFIG_NET_RX_BUSY_POLL
> 
> Is there a way to do this in C instead of the pre-processor. That way all
> the code gets build tested. (Is there a config with disabled
> NET_RX_BUSY_POLL?)
> 
 
How about defining a function to replace the pre-processor:

static inline bool is_net_rx_busy_poll()
{
#ifdef CONFIG_NET_RX_BUSY_POLL
        return true;
#else
        return false;
#endif
}

CONFIG_PREEMPT_RT=y && CONFIG_NETCONSOLE=y will cause NET_RX_BUSY_POLL
disabled.


Kind regards,
 
Ding Meng