net: fec: add rx_shift to indicate the extra bytes padded in front of RX frame

The FEC of some platforms supports RX FIFO shift-16, it means the actual
frame data starts at bit 16 of the first word read from RX FIFO aligning
the Ethernet payload on a 32-bit boundary. The MAC writes two additional
bytes in front of each frame received into the RX FIFO. Currently, the
fec_enet_rx_queue() updates the data_start, sub_len and the rx_bytes
statistics by checking whether FEC_QUIRK_HAS_RACC is set. This makes the
code less concise, so rx_shift is added to represent the number of extra
bytes padded in front of the RX frame. Furthermore, when adding separate
RX handling functions for XDP copy mode and zero copy mode in the future,
it will no longer be necessary to check FEC_QUIRK_HAS_RACC to update the
corresponding variables.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260205085742.2685134-4-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: WeiFang-NXP

drivers/net/ethernet/freescale/fec.h

@@ -643,6 +643,7 @@ struct fec_enet_private {
 	struct pm_qos_request pm_qos_req;
 
 	unsigned int tx_align;
+	unsigned int rx_shift;
 
 	/* hw interrupt coalesce */
 	unsigned int rx_pkts_itr;

drivers/net/ethernet/freescale/fec_main.c

@@ -1800,22 +1800,14 @@ fec_enet_rx_queue(struct net_device *ndev, u16 queue_id, int budget)
 	struct	bufdesc_ex *ebdp = NULL;
 	int	index = 0;
 	bool	need_swap = fep->quirks & FEC_QUIRK_SWAP_FRAME;
+	u32 data_start = FEC_ENET_XDP_HEADROOM + fep->rx_shift;
 	struct bpf_prog *xdp_prog = READ_ONCE(fep->xdp_prog);
 	u32 ret, xdp_result = FEC_ENET_XDP_PASS;
-	u32 data_start = FEC_ENET_XDP_HEADROOM;
+	u32 sub_len = 4 + fep->rx_shift;
 	int cpu = smp_processor_id();
 	struct xdp_buff xdp;
 	struct page *page;
 	__fec32 cbd_bufaddr;
-	u32 sub_len = 4;
-
-	/*If it has the FEC_QUIRK_HAS_RACC quirk property, the bit of
-	 * FEC_RACC_SHIFT16 is set by default in the probe function.
-	 */
-	if (fep->quirks & FEC_QUIRK_HAS_RACC) {
-		data_start += 2;
-		sub_len += 2;
-	}
 
 #if defined(CONFIG_COLDFIRE) && !defined(CONFIG_COLDFIRE_COHERENT_DMA)
 	/*
@@ -1848,9 +1840,7 @@ fec_enet_rx_queue(struct net_device *ndev, u16 queue_id, int budget)
 		/* Process the incoming frame. */
 		ndev->stats.rx_packets++;
 		pkt_len = fec16_to_cpu(bdp->cbd_datlen);
-		ndev->stats.rx_bytes += pkt_len;
-		if (fep->quirks & FEC_QUIRK_HAS_RACC)
-			ndev->stats.rx_bytes -= 2;
+		ndev->stats.rx_bytes += pkt_len - fep->rx_shift;
 
 		index = fec_enet_get_bd_index(bdp, &rxq->bd);
 		page = rxq->rx_buf[index];
@@ -4603,6 +4593,11 @@ fec_probe(struct platform_device *pdev)
 
 	ndev->max_mtu = fep->max_buf_size - VLAN_ETH_HLEN - ETH_FCS_LEN;
 
+	if (fep->quirks & FEC_QUIRK_HAS_RACC)
+		fep->rx_shift = 2;
+	else
+		fep->rx_shift = 0;
+
 	ret = register_netdev(ndev);
 	if (ret)
 		goto failed_register;