netdev - RE: [PATCH] net: fec: fix regression on i.MX28 introduced by rx

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Date:	Wed, 8 Oct 2014 08:54:58 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Sergei Shtylyov' <sergei.shtylyov@...entembedded.com>,
	Lothar Waßmann <LW@...O-electronics.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"David S. Miller" <davem@...emloft.net>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Frank Li <Frank.Li@...escale.com>,
	"Fabio Estevam" <fabio.estevam@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: fec: fix regression on i.MX28 introduced by
 rx_copybreak support

From: Sergei Shtylyov
> On 10/07/2014 05:19 PM, 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 <LW@...O-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
> [...]
> > @@ -1348,7 +1360,7 @@ fec_enet_new_rxbdp(struct net_device *ndev, struct bufdesc *bdp, struct
> sk_buff
> >   }
> >
> >   static bool fec_enet_copybreak(struct net_device *ndev, struct sk_buff **skb,
> > -			       struct bufdesc *bdp, u32 length)
> > +			       struct bufdesc *bdp, u32 length, int swap)
> 
>     'bool swap' perhaps?
> 
> > @@ -1393,6 +1408,7 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
> >   	u16	vlan_tag;
> >   	int	index = 0;
> >   	bool	is_copybreak;
> > +	bool need_swap = id_entry->driver_data & FEC_QUIRK_SWAP_FRAME;
> 
>     ... especially talking this into account...

Hmmm... in that case you may not want the compiler to convert the bit value
to a 'bool' at all.

Passing 'id_entry->driver_data' through (that doesn't look like a field name for
'quirk flags) would generate better code.

Even better would be to reference the flag directly from 'ndev'.
A pointer indirection for the test if probably faster then passing another argument.

	David