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>
3ac72b7b63