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

[Florian Bezdeka]

On Tue, 2026-06-23 at 09:46 +0000, Kwapulinski, Piotr wrote:
> > -----Original Message-----
> > From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf Of Ding Meng via Intel-wired-lan
> > Sent: Monday, June 22, 2026 6:13 AM
> > To: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel, Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>; andrew+netdev@xxxxxxx; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; Kiszka, Jan <jan.kiszka@xxxxxxxxxxx>; Bezdeka, Florian <florian.bezdeka@xxxxxxxxxxx>
> > Cc: intel-wired-lan@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; meng.ding@xxxxxxxxxxx; wq.wang@xxxxxxxxxxx
> > Subject: [Intel-wired-lan] [PATCH net] igc: Fix RX HW timestamp reporting when NET_RX_BUSY_POLL is disabled
> > 
> > When CONFIG_NET_RX_BUSY_POLL is deactivated, fetching RX HW timestamps from the NIC no longer works as expected.
> > 
> > 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.
> > 
> > Fixes: 069b142f5819 ("igc: Add support for PTP .getcyclesx64()")
> > Co-developed-by: Florian Bezdeka <florian.bezdeka@xxxxxxxxxxx>
> > Signed-off-by: Florian Bezdeka <florian.bezdeka@xxxxxxxxxxx>
> > Signed-off-by: Ding Meng <meng.ding@xxxxxxxxxxx>
> > ---
> > drivers/net/ethernet/intel/igc/igc_main.c | 38 ++++++++++++++++-------
> > 1 file changed, 26 insertions(+), 12 deletions(-)
> > 
> > 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
> > +	skb_shinfo(skb)->tx_flags |= SKBTX_HW_TSTAMP_NETDEV;
> > +	skb_hwtstamps(skb)->netdev_data = ctx->rx_ts; #else
> > +	struct igc_inline_rx_tstamps *tstamps;
> Please move at the top of the function and add:

That would trigger a "unused variable" warning in the
CONFIG_NET_RX_BUSY_POLL case.

Btw: I was really confused that the #else statement moved to the end of
the previous line. Might someone be using a wrongly configured mail
client here?

Florian

> Reviewed-by: Piotr Kwapulinski <piotr.kwapulinski@xxxxxxxxx
> 
> > +
> > +	tstamps = ctx->rx_ts;
> > +	skb_hwtstamps(skb)->hwtstamp = igc_ptp_rx_pktstamp(adapter,
> > +							   tstamps->timer0);
> > +#endif
> > +}
> > +

[snip]