Jeff,
I just read your message of Feb 10th, 2005 regarding the cable problems
of natsemi.c. My investigation started late last week. On Feb 14th, I
got serious and nailed it down. I submitted a patch of my own without
realizing there was other work in progress on the same issue. Please
consider replacing the patch you didn't like with mine.
What was happening with my DP83815D was that the TSTDAT value being read
in the do_cable_magic function was near 0x1f, regardless of cable
length. The code that fixes short cable problems actually works for
short cables, but messes up long ones. The cable magic couldn't figure
out the length of the cable and always applied the fix. I went looking
for the history of this patch on the Internet and found a DP83815 Linux
driver written and maintained by National Semiconductor. I was struck
by the difference in the initialization sequences. natsemi.c always
applies the sequence documented for the DP83815B. dp83815.c applies
different sequences for chip revisions B, C, and D+. I used the D
initialization for my D chip, and again watched the values being
returned from TSTDAT in do_cable magic. A 1m cable returned something
like 0xF8 and a 90m cable return something like 0xB8. Now the register
was returning a value like it must have done with previous revisions of
the chip. The magic is properly applied in the proper situation.
Since there is no public documentation on these PHY manipulations, I
minimized the 'fix' to the setting of the DSPCFG register. If I only
turn on the bit that makes the coefficient readable, do_cable_magic now
appears to have the right information to decide the cable length
automatically.
Ain't life great?
Gary
in reply to http://oss.sgi.com/archives/netdev/2005-02/msg00396.html
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Gary Spiess (Gary.Spiess@xxxxxxxxxxxx)
MobileLan Wireless Products Group, Intermec Technology Corp
voice: 319 369-3580 fax: 319 369-3804
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