Re: possible bug fix for 82550-based fxp packet truncation problem

> Don Lewis <truckman_at_freebsd.org> wrote
>   in <200305220823.h4M8N9M7075271_at_gw.catspoiler.org>:
> 
> truckman> If you are using one of my previous patches which worked around the
> truckman> problem by disabling the IPCB mode, you may want to try the patch below.
> 
>  This works fine in my environment.  My fxp has the following id:
> 
>   fxp0_at_pci7:2:0:  class=0x020000 card=0x10508086 chip=0x12298086 rev=0x0d hdr=0x00
> 
>  Without any patches, packets whose size is 216+(N*1480) are dropped
>  as I reported on -stable before.  Similarly I tried "ping -s X" with
>  various payload size from X=1 to X=6000 in the system using the
>  patched kernel, but no error is reported.  
> 

Just to let people know, I have been trying to investigate this, but
my time has been somewhat limited lately. The original reason I turned
off the IP checksumming on transmit was that there was one test case
where the chip seemed to be generating improper checksums. That is,
if you did something like: ping -s 1473 <otherhost>. This would result
in a full sized frame, plus a small IP fragment containing just one
byte of data. On the machine I used for testing, the small fragment
was rejected by the host on the other side due to a bad header checksum.

The machine I was testing on was an old Gateway 2000 Pentium 166 system.
I have since tried re-enabling the IP checksumming on transmit and
re-run the test on an Athlon system, and everything works correctly.
(Coincidentally, I ran a similar test on a PowerPC 440GP board running
VxWorks and everything worked correctly there too.)

So my theory is that the original bug I found was not due to the chip
computing bad checksums, although I'm at a loss to say what the cause
really was. And I don't have that particular machine handy anymore. :/

As an experiment, you might try re-enabling the IP header checksumming to
see just what happens. If the ping -s 1473 tests succeeds, then maybe
I was smoking crack and we should turn IP checksumming back on.

-Bill

--
=============================================================================
-Bill Paul            (510) 749-2329 | Senior Engineer, Master of Unix-Fu
                 wpaul_at_windriver.com | Wind River Systems
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      "If stupidity were a handicap, you'd have the best parking spot."
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