From: Lothar Waßmann
> David Laight wrote:
> > From: Eric Dumazet
> > > On Tue, 2014-10-07 at 15:19 +0200, Lothar Wamann wrote:
> > > > commit 1b7bde6d659d ("net: fec: implement rx_copybreak to improve rx
> > > > performance")
> > > > introduced a regression for i.MX28. The swap_buffer() function doing
> > > > the endian conversion of the received data on i.MX28 may access memory
> > > > beyond the actual packet size in the DMA buffer. fec_enet_copybreak()
> > > > does not copy those bytes, so that the last bytes of a packet may be
> > > > filled with invalid data after swapping.
> > > > This will likely lead to checksum errors on received packets.
> > > > E.g. when trying to mount an NFS rootfs:
> > > > UDP: bad checksum. From 192.168.1.225:111 to 192.168.100.73:44662 ulen
> > > > 36
> > > >
> > > > Do the byte swapping and copying to the new skb in one go if
> > > > necessary.
> > > >
> > > > Signed-off-by: Lothar Wamann <l...@karo-electronics.de>
> > > > ---
> > > > drivers/net/ethernet/freescale/fec_main.c | 25
> > > > +++++++++++++++++++++----
> > > > 1 file changed, 21 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > > > b/drivers/net/ethernet/freescale/fec_main.c
> > > > index 87975b5..eaaebad 100644
> > > > --- a/drivers/net/ethernet/freescale/fec_main.c
> > > > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > > > @@ -339,6 +339,18 @@ static void *swap_buffer(void *bufaddr, int len)
> > > > return bufaddr;
> > > > }
> > > >
> > > > +static void *swap_buffer2(void *dst_buf, void *src_buf, int len)
> > > > +{
> > > > + int i;
> > > > + unsigned int *src = src_buf;
> > > > + unsigned int *dst = dst_buf;
> > > > +
> > > > + for (i = 0; i < DIV_ROUND_UP(len, 4); i++, src++, dst++)
> > > > + *dst = cpu_to_be32(*src);
> > >
> > > No need for the DIV :
> > >
> > > for (i = 0; i < len; i += sizeof(*dst), src++, dst++)
> > > *dst = cpu_to_be32(*src);
> > >
> > > Also are you sure both src/dst are aligned to word boundaries, or is
> > > this architecture OK with possible misalignment ?
> >
> > I wondered about that as well.
> > I wouldn't have expected ppc to support misaligned transfers, and you'd also
> > want to make sure that cpu_to_be(*src) was using a byte-swapping
> > instruction.
> > Hmmm... cpu_to_be() doesn't sound like the right 'swap' macro name.
> >
> ??? So what is cpu_to_be32() then?
> The new swap function is an exact copy of the original one already in
> use except for the fact that it uses distinct source and destination
> buffers.
cpu_to_be32() is for converting a 'cpu' endianness value to 'big-endian'.
Here you are processing receive data - so you probably want be32_to_cpu().
(Yes, I know they are functionally identical....)
Alternatively, since these aren't actually 32bit numbers and you know
whether you want to swap, something like the __swab32p() from swab.h
- but I'm not entirely sure that one is expected to be used.
Clearly you are well inside the ppc 'endianness' hell.
David
