[PATCH net] net: lan966x: fix the DB dataptr of frames from ndo_xdp_xmit

[Daniel Machon <daniel.machon@microchip.com>]

lan966x_fdma_xmit_xdpf() transmits both XDP_TX frames and xdp_frames
from ndo_xdp_xmit, and builds the DB with
lan966x_fdma_xdp_tx_dataptr_cb(), which adds XDP_PACKET_HEADROOM to the
stored DMA address.

Before this patch, the headroom is also added for xdp_frames. For
XDP_TX the stored address is the start of the page pool page, but for an
xdp_frame it is the mapping of the IFH placed in front of the frame
data, so frames from ndo_xdp_xmit are read from XDP_PACKET_HEADROOM
bytes after their IFH.

Use the plain tx dataptr callback for xdp_frames.

Found by an AI code review agent. Reproduced on a lan9668 board with an
XDP program redirecting frames from one port to another: none of the 20
frames arrived intact on the link partner. With the fix all 20 did.

Fixes: 29cc3a66a81d ("net: lan966x: use FDMA library for adding DCB's in the tx path")
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
---
 drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index a7940eca5df31..8ea86b800af75 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -686,7 +686,8 @@ int lan966x_fdma_xmit_xdpf(struct lan966x_port *port, void *ptr, u32 len)
 		       FDMA_DCB_STATUS_BLOCKO(0) |
 		       FDMA_DCB_STATUS_BLOCKL(next_dcb_buf->len),
 		       &fdma_nextptr_cb,
-		       &lan966x_fdma_xdp_tx_dataptr_cb);
+		       len ? &lan966x_fdma_xdp_tx_dataptr_cb :
+			     &lan966x_fdma_tx_dataptr_cb);
 
 	/* Start the transmission */
 	lan966x_fdma_tx_start(tx);

---
base-commit: 6430fb7f1cc4e329e386521b7b208df443de92f2
change-id: 20261023-lan966x-xdp-xmit-dataptr-b0aee56bcdb8

Best regards,
-- 
Daniel Machon <daniel.machon@microchip.com>