net: fec: align IP header in hardware

The FEC receive accelerator (RACC) supports shifting the data payload of
received packets by 16-bits, which aligns the payload (IP header) on a
4-byte boundary, which is, if not required, at least strongly suggested
by the Linux networking layer.

Without this patch, a huge number of alignment faults will be taken by the
IP stack, as seen in /proc/cpu/alignment:

	~/$ cat /proc/cpu/alignment
	User:		0
	System:		72645 (inet_gro_receive+0x104/0x27c)
	Skipped:	0
	Half:		0
	Word:		0
	DWord:		0
	Multi:		72645
	User faults:	3 (fixup+warn)

This patch was suggested by Andrew Lunn in this message to linux-netdev:
	http://marc.info/?l=linux-arm-kernel&m=147465452108384&w=2

and adapted from a patch by Russell King from 2014:
	http://git.arm.linux.org.uk/cgit/linux-arm.git/commit/?id=70d8a8a

Signed-off-by: Eric Nelson <eric@nelint.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 3fb11f929adc85f70c6bb4c43c6e55dc3a4a7bff..692ee248e48640cd33d725096aafe52a74fa0c50 100644 (file)
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -180,6 +180,7 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet MAC address");
 /* FEC receive acceleration */
 #define FEC_RACC_IPDIS         (1 << 1)
 #define FEC_RACC_PRODIS                (1 << 2)
+#define FEC_RACC_SHIFT16       BIT(7)
 #define FEC_RACC_OPTIONS       (FEC_RACC_IPDIS | FEC_RACC_PRODIS)
 
 /*
@@ -945,9 +946,11 @@ fec_restart(struct net_device *ndev)
 
 #if !defined(CONFIG_M5272)
        if (fep->quirks & FEC_QUIRK_HAS_RACC) {
-               /* set RX checksum */
                val = readl(fep->hwp + FEC_RACC);
+               /* align IP header */
+               val |= FEC_RACC_SHIFT16;
                if (fep->csum_flags & FLAG_RX_CSUM_ENABLED)
+                       /* set RX checksum */
                        val |= FEC_RACC_OPTIONS;
                else
                        val &= ~FEC_RACC_OPTIONS;
@@ -1428,6 +1431,12 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
                prefetch(skb->data - NET_IP_ALIGN);
                skb_put(skb, pkt_len - 4);
                data = skb->data;
+
+#if !defined(CONFIG_M5272)
+               if (fep->quirks & FEC_QUIRK_HAS_RACC)
+                       data = skb_pull_inline(skb, 2);
+#endif
+
                if (!is_copybreak && need_swap)
                        swap_buffer(data, pkt_len);