[U-Boot] T4240 SGMII "Tx buffer not ready"

[Danny Gale <Daniel.Gale@coloradoengineeringinc.com>]

Hi everybody,

We're trying to bring up a 100M/1G ethernet interface on a custom T4240 
board over SGMII and running into the following errors:

Immediately after board reset:
=> ping 192.168.1.53
Using FM2 at DTSEC6 device
FM2 at DTSEC6: Tx error
FM2 at DTSEC6: Rx error
ping failed; host 192.168.1.53 is not alive

On any subsequent attempts:
=> ping 192.168.1.53
Using FM2 at DTSEC6 device
FM2 at DTSEC6: Tx buffer not ready. txbd->status = 0x8800
FM2 at DTSEC6: Tx buffer not ready. txbd->status = 0x8800
ping failed; host 192.168.1.53 is not alive

We're running from u-boot 2014.07-rc3. Our custom board ethernet 
bring-up code is closely based on the code for the t4rdb. The SGMII 
interface hardware is coming up out of reset (we're seeing the interface 
toggling at the expected rate) but it looks like u-boot isn't 
communicating with it properly. There's very little information to go on 
in the source code related to this error (drivers/net/fm/eth.c, in 
fm_eth_send). What can cause this problem?

Here are my environment variables related to networking:
eth1addr=00:50:C2:72:01:04
eth2addr=00:50:C2:72:01:06
eth3addr=00:50:C2:72:01:08
eth4addr=00:50:C2:72:01:0a
eth5addr=00:50:C2:72:01:0c
eth6addr=00:50:C2:72:01:0e
ethact=FM2 at DTSEC6
ethaddr=00:50:C2:72:01:02
ethprime=FM2 at DTSEC6
ipaddr=192.168.1.230
netmask=255.255.255.0
gatewayip=192.168.1.11

Thanks for any help you can provide. Let me know if you need more 
information,
Danny Gale
daniel.gale at coloradoengineeringinc.com