Messages in this thread | | | Date | Tue, 28 Oct 2014 14:30:36 +0100 | From | Lothar Waßmann <> | Subject | Re: [PATCHv2 6/6] net: fec: fix regression on i.MX28 introduced by rx_copybreak support |
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Hi,
David Laight wrote: > From: Lothar Waßmann > > David Laight wrote: > > > From: Lothar Waßmann > > > > 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 <LW@KARO-electronics.de> > > > > --- > > > > drivers/net/ethernet/freescale/fec_main.c | 25 +++++++++++++++++++++---- > > > > 1 file changed, 21 insertions(+), 4 deletions(-) > > > > > > > > @@ -1455,7 +1472,7 @@ 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 (fep->quirks & FEC_QUIRK_SWAP_FRAME) > > > > + if (!is_copybreak && need_swap) > > > > swap_buffer(data, pkt_len); > > > > > > It has to be better to set the 'copybreak' limit to be larger than the > > > maximum frame size and so always go through the 'copybreak' paths. > > > > > Since the copybreak support is all about performance optimistation, we > > should IMO buy the additional advantage for i.MX28 by not having to > > access the buffer twice (once for copying and once again for swapping). > > You definitely want to do the byteswap at the same time as the copy. > > The point I'm trying to make that if you need to do the byteswap you > probably might as well copy the data to an skb of the correct size at > the same time. > Certainly I'd expect the 'break even' length will be much higher. > I didn't implement the copybreak support. I'm only trying to fix a bug it introduced for i.MX28. So, I won't mess with the copybreak parameters.
Lothar Waßmann -- ___________________________________________________________
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