[U-Boot] Bug: RealTek chipset does not work at 100/1000 Mbps

[Mike <shotgunjack108@yahoo.com>]

Hello, I have been experiencing VERY slow TFTP speeds using the Realtek
RTL8111GS-CG Ethernet chipset. The board I am using is a Minnowboard Max
(revision A2) and the version of U-Boot is 2015.10-rc3.

After booting the board into the U-Boot command prompt I set the envs
'ipaddr' and 'serverip' and run the command 'tftp 0x3000000 <my file>'.
The file is downloaded at 700-800 KiB/s, even though the board is
directly connected to my laptop and the link speed is 100 Mbs (courtesy
of ethtool). Performing the same test but with the board and laptop
connected to a switch doesn't change the transfer speed. Enabling
DEBUG_RTL8169 in drivers/net/rtl8169.c results in the following error
message being displayed:

eth_rtl8169: 1000Mbps Full-duplex operation, TBI Link Failed!

Attempting to force gigabit speeds in the uboot driver results in a
TFTP download rate of up to 1.5 MiB/s, and ethtool shows a link speed
of 1000Mbps. Looking at the rtl8111 PHY status register I can see that
the ethernet chip also thinks it is in a full duplex, 1000Mbps
connection. Forcing the chip to 100Mbit (half and full duplex) results
in transfer rates of 700-800 KB/s.Looking at the actual packets sent
during the TFTP session shows no large number of missed packets,
retries etc.; nothing unusual.

After booting the board into Linux I am able to establish a 1 gigabit
connection and achieve transfer rates of over 100 MB/s, so its most
likely something to do with U-Boot's rtl8169 driver not setting up the
chip correctly. I would greatly appreciate if someone with more
experience in this field can look into this; it is likely that this
issue affects multiple Realtek Ethernet chipsets.

Lastly, creating a ROM with an invalid (blank) vga.bin increases TFTP
speeds to 2.4 MB/s; which is completely counterintuitive.


Please let me know if I can be of any help, I would really like to get
to the bottom of this.


-Mike