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

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

[David Jander]

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?

Best regards,

-- 
David Jander
Protonic Holland.

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.

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

[David Jander]

On Wed, 28 Oct 2015 11:14:14 +0000
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> 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...

Sorry, I somehow assumed it was obvious I'd report against latest mainline...
I'm on 4.3-rc7.

Best regards,

-- 
David Jander
Protonic Holland.

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

[Fabio Estevam]

On Wed, Oct 28, 2015 at 9:19 AM, David Jander <david@protonic.nl> wrote:

> Sorry, I somehow assumed it was obvious I'd report against latest mainline...
> I'm on 4.3-rc7.

Are you able to find out a previous kernel version that does not
exhibit this failure?

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

[David Jander]

On Wed, 28 Oct 2015 10:31:17 -0200
Fabio Estevam <festevam@gmail.com> wrote:

> On Wed, Oct 28, 2015 at 9:19 AM, David Jander <david@protonic.nl> wrote:
> 
> > Sorry, I somehow assumed it was obvious I'd report against latest
> > mainline... I'm on 4.3-rc7.
> 
> Are you able to find out a previous kernel version that does not
> exhibit this failure?

I can search further down, but 4.1 is also broken.
Are there specific changes or versions you are suspicious of?
Russel mentioned something similar being fixed in the past... any pointers to
this fix, so I can investigate whether this has any relation?

Best regards,

-- 
David Jander
Protonic Holland.

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

[Fabio Estevam]

On Wed, Oct 28, 2015 at 10:36 AM, David Jander <david@protonic.nl> wrote:

> I can search further down, but 4.1 is also broken.
> Are there specific changes or versions you are suspicious of?

I was just trying to understand if this was a regression or if it has
always been broken.