[PATCH net 2/6] igc: only strip RX timestamp header from first buffer

[Tony Nguyen <anthony.l.nguyen@intel.com>]

From: Paul Moses <p@1g4.org>

igc_clean_rx_irq() strips IGC_TS_HDR_LEN whenever a descriptor reports
IGC_RXDADV_STAT_TSIP. For multi-buffer packets, continuation descriptors
retain TSIP even though the inline timestamp is present only in the first
RX buffer.

Subtracting the header length from each continuation buffer truncates
jumbo packets by 16 bytes per continuation and leaves the packet length
larger than the received data.

Only consume the timestamp header when skb is NULL, which identifies the
first buffer of a new packet. An skb carried in rx_ring->skb remains
non-NULL when packet assembly resumes in a later NAPI poll.

Link: https://lore.kernel.org/all/20260625-igb-rx-ts-fix-v3-1-99b3efa08dca@aweta.nl/
Fixes: e1ed4f92a625 ("igc: Refactor Rx timestamp handling")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Moses <p@1g4.org>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 95f7747b347b..b94a08791102 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2658,7 +2658,8 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
 
 		pktbuf = page_address(rx_buffer->page) + rx_buffer->page_offset;
 
-		if (igc_test_staterr(rx_desc, IGC_RXDADV_STAT_TSIP)) {
+		if (!skb &&
+		    igc_test_staterr(rx_desc, IGC_RXDADV_STAT_TSIP)) {
 			ctx.rx_ts = pktbuf;
 			pkt_offset = IGC_TS_HDR_LEN;
 			size -= IGC_TS_HDR_LEN;
-- 
2.47.1