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 3fb11f9..692ee24 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -180,6 +180,7 @@
/* 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 @@
#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 @@
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);