[PATCH net 1/6] igc: Fix RX HW timestamp reporting when NET_RX_BUSY_POLL is disabled

[PATCH net 1/6] igc: Fix RX HW timestamp reporting when NET_RX_BUSY_POLL is disabled

[Tony Nguyen]

From: Ding Meng <meng.ding@siemens.com>

When CONFIG_NET_RX_BUSY_POLL is deactivated, fetching RX HW timestamps
from the NIC no longer works as expected, often resulting in incorrect
or negative values such as "HW raw -121948.050407424".

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. This results in incorrect
timestamps.

Fix this by populating the hwtstamp field with the correct timestamp
in the default timer when CONFIG_NET_RX_BUSY_POLL is disabled.
The "igc_adapter" is passed to igc_construct_skb() to enable
igc_ptp_rx_pktstamp() to access the necessary adapter details for
adjusting the timestamp.

Test case:
 Disable CONFIG_NET_RX_BUSY_POLL.
 Sender:
 # tools/testing/selftests/net/timestamping en0 \
        SOF_TIMESTAMPING_TX_HARDWARE PTPV2 IP_MULTICAST_LOOP
 Receiver:
 # tools/testing/selftests/net/timestamping en0 \
        SOF_TIMESTAMPING_RX_HARDWARE SOF_TIMESTAMPING_RAW_HARDWARE PTPV2

Before patch, receiver prints
 HW raw -121948.050407424
After patch, receiver prints
 HW raw 1760648763.746974064

Fixes: 069b142f5819 ("igc: Add support for PTP .getcyclesx64()")
Cc: stable@vger.kernel.org
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>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Piotr Kwapulinski <piotr.kwapulinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 41 ++++++++++++++++-------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 1fb5f3cbe93c..95f7747b347b 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1989,7 +1989,29 @@ 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)
+{
+#ifndef CONFIG_NET_RX_BUSY_POLL
+	struct igc_inline_rx_tstamps *tstamps;
+#endif
+
+	if (!ctx->rx_ts)
+		return;
+
+#ifndef CONFIG_NET_RX_BUSY_POLL
+	tstamps = ctx->rx_ts;
+	skb_hwtstamps(skb)->hwtstamp = igc_ptp_rx_pktstamp(adapter,
+							   tstamps->timer0);
+#else
+	skb_shinfo(skb)->tx_flags |= SKBTX_HW_TSTAMP_NETDEV;
+	skb_hwtstamps(skb)->netdev_data = ctx->rx_ts;
+#endif
+}
+
+static struct sk_buff *igc_construct_skb(struct igc_adapter *adapter,
+					 struct igc_ring *rx_ring,
 					 struct igc_rx_buffer *rx_buffer,
 					 struct igc_xdp_buff *ctx)
 {
@@ -2010,10 +2032,7 @@ static struct sk_buff *igc_construct_skb(struct igc_ring *rx_ring,
 	if (unlikely(!skb))
 		return NULL;
 
-	if (ctx->rx_ts) {
-		skb_shinfo(skb)->tx_flags |= SKBTX_HW_TSTAMP_NETDEV;
-		skb_hwtstamps(skb)->netdev_data = ctx->rx_ts;
-	}
+	igc_construct_skb_timestamps(adapter, skb, ctx);
 
 	/* Determine available headroom for copy */
 	headlen = size;
@@ -2683,7 +2702,7 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
 		else if (ring_uses_build_skb(rx_ring))
 			skb = igc_build_skb(rx_ring, rx_buffer, &ctx.xdp);
 		else
-			skb = igc_construct_skb(rx_ring, rx_buffer, &ctx);
+			skb = igc_construct_skb(adapter, rx_ring, rx_buffer, &ctx);
 
 		/* exit if we failed to retrieve a buffer */
 		if (!xdp_res && !skb) {
@@ -2735,7 +2754,8 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
 	return total_packets;
 }
 
-static struct sk_buff *igc_construct_skb_zc(struct igc_ring *ring,
+static struct sk_buff *igc_construct_skb_zc(struct igc_adapter *adapter,
+					    struct igc_ring *ring,
 					    struct igc_xdp_buff *ctx)
 {
 	struct xdp_buff *xdp = &ctx->xdp;
@@ -2757,10 +2777,7 @@ static struct sk_buff *igc_construct_skb_zc(struct igc_ring *ring,
 		__skb_pull(skb, metasize);
 	}
 
-	if (ctx->rx_ts) {
-		skb_shinfo(skb)->tx_flags |= SKBTX_HW_TSTAMP_NETDEV;
-		skb_hwtstamps(skb)->netdev_data = ctx->rx_ts;
-	}
+	igc_construct_skb_timestamps(adapter, skb, ctx);
 
 	return skb;
 }
@@ -2772,7 +2789,7 @@ static void igc_dispatch_skb_zc(struct igc_q_vector *q_vector,
 	struct igc_ring *ring = q_vector->rx.ring;
 	struct sk_buff *skb;
 
-	skb = igc_construct_skb_zc(ring, ctx);
+	skb = igc_construct_skb_zc(q_vector->adapter, ring, ctx);
 	if (!skb) {
 		ring->rx_stats.alloc_failed++;
 		set_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &ring->flags);
-- 
2.47.1

Re: [PATCH net 1/6] igc: Fix RX HW timestamp reporting when NET_RX_BUSY_POLL is disabled

[Jakub Kicinski]

On Thu,  1 Oct 2026 15:24:34 -0700 Tony Nguyen wrote:
> When CONFIG_NET_RX_BUSY_POLL is deactivated, fetching RX HW timestamps
> from the NIC no longer works as expected, often resulting in incorrect
> or negative values such as "HW raw -121948.050407424".
> 
> 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. This results in incorrect
> timestamps.
> 
> Fix this by populating the hwtstamp field with the correct timestamp
> in the default timer when CONFIG_NET_RX_BUSY_POLL is disabled.
> The "igc_adapter" is passed to igc_construct_skb() to enable
> igc_ptp_rx_pktstamp() to access the necessary adapter details for
> adjusting the timestamp.

looks like a driver workaround for a generic problem
a better fix is likely needed here