Re: DSA mv88e6xxx RX frame errors and TCP/IP RX failure

Andrew Lunn
2017-08-31T17:41:50Z

> > I did fix an issue recently with that. See
> >
> > commit fbbeefdd21049fcf9437c809da3828b210577f36
> > Author: Andrew Lunn <andrew@lunn.ch>
> > Date: Sun Jul 30 19:36:05 2017 +0200
> >
> > net: fec: Allow reception of frames bigger than 1522 bytes
> >
> > The FEC Receive Control Register has a 14 bit field indicating the
> > longest frame that may be received. It is being set to 1522. Frames
> > longer than this are discarded, but counted as being in error.
> >
> > When using DSA, frames from the switch has an additional header,
> > either 4 or 8 bytes if a Marvell switch is used. Thus a full MTU frame
> > of 1522 bytes received by the switch on a port becomes 1530 bytes when
> > passed to the host via the FEC interface.
> >
> > Change the maximum receive size to 2048 - 64, where 64 is the maximum
> > rx_alignment applied on the receive buffer for AVB capable FEC
> > cores. Use this value also for the maximum receive buffer size. The
> > driver is already allocating a receive SKB of 2048 bytes, so this
> > change should not have any significant effects.
> >
> > Tested on imx51, imx6, vf610.
> >
> > Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> > Signed-off-by: David S. Miller <davem@davemloft.net>
> >
> >
> > However, this is was of an all/nothing problem. All frames with the
> > full MTU were getting dropped, where as i think you are only seeing a
> > few dropped?
> >
>
> Andrew,
>
> Indeed this does resolve the issue. I see a burst of FIFO overruns
> initially when receiving an iperf bandwidth test but that would be
> caused by the IMX6 errata and should be mitigated via pause frames.
> After that short burst I see no other errors and iperf works fine.
>
> Should we get this patch in the linux-stable tree for the 4.9 kernel?

Hi David

Please could you add

fbbeefdd2104 ("net: fec: Allow reception of frames bigger than 1522 bytes")

to stable.

Thanks
Andrew