Port of the new em(4) to RELENG_6 and some problems with 82540EM

[Eygene Ryabinkin]

Jack, good day.

I happened to make a quick and dirty patch for your latest (for the
16.05.2007) em(4) driver from 7-CURRENT. I had seen that you mentioned
TSO and 6.3, so I assume that you're going to merge the driver to
the RELENG_6 someday, so maybe my effort may be helpful.

To my problems.

I have the '82540EM Gigabit Ethernet Controller' branded card
(PWLA8390MT) and I am currently expiriencing troubles with the
Gigabit switch (D-Link DGS-1008, the cheap one). Plugged into that
switch I have

 - broken packets and SSH messages 'Disconnecting: Corrupted MAC
 on input.' when checksumming is turned on and gigabit speed,

 - abyssmal rates for the HTTP downloads (about 10Mbit/sec) when
 checksums are turned off and the speed is gigabit again,

 - having switched the media on the adapter to the 100BaseTX
 full-duplex, but still using the same switch the speed drops to
 200Kbit/sec,

 - using another D-Link switch (sorry, have no other brand in
 hand) the above situation is completely reproducible.

 - working in the half-duplex mode (for 10BaseT/UTP and 100BaseTX)
 I have no problems to reach the 90% of the theoretical bandwidth
 of the link via HTTP either with checksums enabled or disabled.

So, the full-duplex mode is not usable to me now. If someone can
help in this situation, I am all ears.

I thought that new driver may introduce some fixes, but it isn't:
the situation is the same. I will continue my investigations, but
just in case you're interested in my port, it is available from

    http://codelabs.ru/patches/fbsd/em-6.5.0-initial.patch.bz2

RELENG_6 and 7-CURRENT sources were CVSupped yesterday, 16 May 2007.
TSO-related stuff is completely disabled for the RELENG_6.

My limited testing of the driver revealed no problems yet, but if
they will arise I will report them.
-- 
Eygene