BUG: fsl FEC ethernet tx checksum offloading doesn't work with RMII interface

[Russell King - ARM Linux]

On Wed, Oct 28, 2015 at 10:48:54AM +0100, David Jander wrote:
> 
> Hi all,
> 
> I was unable to figure out who's maintaining
> drivers/net/ethernet/freescale/fec_main.c, so I hope someone can help out on
> this list...
> 
> We have a board with a RMII phy connected to an i.MX6S. The hardware seems to
> be ok, since I can receive and transmit ethernet frames without drops or
> errors. However only simple things like ping and dhcp seemed to work. TCP/IP
> connections could not be made. When looking at both ends with tcpdump, I
> realized that all transmitted packages arrived at the other end with the TCP
> and IP header checksums zeroed-out.
> 
> After issuing the following command, TCP/IP started working correctly:
> 
> $ ethtool --offload eth0 tx off
> 
> This works around the issue. For some reason, when the FEC is in RMII mode, it
> isn't filling in the checksums.
> 
> On another board with an RGMII phy the same kernel works fine without the need
> to disable offloading. What can possibly relate this functionality to the
> choice of MAC interface?

You don't mention which kernel version you're using.  There has been a bug
here with older kernels...

-- 
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.