Subject: Realtek 8139 problem on 486.

From: Nikolai Zhubr <[email-masked]>
Date: Sat, 29 May 2021 17:08:02 +0300

Hello all,

I'm observing a problem with Realtek 8139 cards on a couple of 486 
boxes. The respective driver is 8139too. It starts operation 
successfully, obtains an ip address via dhcp, replies to pings steadily, 
but some subsequent communication fails apparently. At least, nfsroot is 
unusable (it gets stuck in "... not responding, still trying" forever), 
and also iperf3 -c xxx when run against a neighbour box on a lan prints 
2-3 lines with some reasonable 7Mbit/s rate, then just prints 0s and 
subsequently throws a panic about output queue full or some such.

My kernel is 4.14.221 at the moment, but I can compile another if 
necessary.
I've already tried the "#define RTL8139_DEBUG 3" and "8139TOO_PIO=y" and 
"#define RX_DMA_BURST 4" and "#define TX_DMA_BURST 4" (in case there is 
a PCI burst issue, as mentioned somewhere) and nothing changed whatsoever.

Some additional notes:
- the problem is 100% reproducable;
- replacing this 8139 card with some entirely different 8139-based card 
changes nothing;
- if I replace this 8139 with a (just random) intel Pro/1000 card, 
everything seem to work fine;
- if I insert this 8139 into some other 486 motherboard (with a 
different chipset), everything seem to work fine again;
- etherboot and pxelinux work fine.

I'm willing to do some debugging but unfortunately I'm not anywhere 
familiar with this driver and network controllers in general, therefore 
I'm asking for some hints/advice first.

Thank you,

Regards,
Nikolai