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

[Marcin Szycik <marcin.szycik@linux.intel.com>]

On 24/06/2026 11:05, Florian Bezdeka via Intel-wired-lan wrote:
> On Tue, 2026-06-23 at 09:46 +0000, Kwapulinski, Piotr wrote:
>>> -----Original Message-----
>>> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf Of Ding Meng via Intel-wired-lan
>>> Sent: Monday, June 22, 2026 6:13 AM
>>> To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel, Przemyslaw <przemyslaw.kitszel@intel.com>; andrew+netdev@lunn.ch; davem@davemloft.net; edumazet@google.com; kuba@kernel.org; pabeni@redhat.com; Kiszka, Jan <jan.kiszka@siemens.com>; Bezdeka, Florian <florian.bezdeka@siemens.com>
>>> Cc: intel-wired-lan@lists.osuosl.org; linux-kernel@vger.kernel.org; netdev@vger.kernel.org; meng.ding@siemens.com; wq.wang@siemens.com
>>> 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@siemens.com>
>>> Signed-off-by: Florian Bezdeka <florian.bezdeka@siemens.com>
>>> Signed-off-by: Ding Meng <meng.ding@siemens.com>
>>> ---
>>> 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.

Put it under #ifndef CONFIG_NET_RX_BUSY_POLL. Variable declarations
need to be on top.

Thanks,
Marcin

> 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@intel.com
>>
>>> +
>>> +	tstamps = ctx->rx_ts;
>>> +	skb_hwtstamps(skb)->hwtstamp = igc_ptp_rx_pktstamp(adapter,
>>> +							   tstamps->timer0);
>>> +#endif
>>> +}
>>> +
> 
> [snip]