Sun Blade 2500 Silver DIMM fan sensor

[Julian Coleman <jdc%coris.org.uk@localhost>]

Hi,

I've just added a driver (auxfan) for the DIMM fan sensor on Sun Blade 2500
Silver machines.  The controller chip is a programmed PIC with no docs.
By comparing the output from Solaris and then the register values, I could
guess at the fan speed values.  Output on my SB2500S is:

  # envstat -d auxfan0
                Current  CritMax  WarnMax  WarnMin  CritMin  Unit
  [auxfan0]
    dimm-fan:      4188                                       RPM

It's possible that I have the speed wrong by 3 or 4 [0], but I think
that's OK.  I couldn't work out how to change the speed (OFW seems to)
nor if there is a fan fault register [1].  The driver should report a
critical state to envsys if the speed is 0 though.

Whilst looking at this, I noticed that the speeds reported for the other
fans were 4x too fast.  Looking at the dbcool driver, it didn't read the
fan characteristics register, which contains a speed divider value.
Reading this and applying the divider gives me fan speeds that match what
Solaris reports.  I'll commit a change [2] shortly after a few more
tests.  It might also change the reported fan values on the SB2500 Red
and SB1500 Red and Silver.

The SB2500S also has a fan near the SCSI disks, but that is a 2-wire fan
and doesn't seem to be monitored.

Regards,

Julian

[0] Adding or subtracting 70 to the divider value in auxfanreg.h results
in similar fan speed values, bu the current value seems correct or nearly.
[1] I plan to disconnect the DIMM fan and check the registers, but when
the weather is a bit cooler.
[2] dbcool patch (WIP) is:
  https://ftp.netbsd.org/pub/NetBSD/misc/jdc/dbcool.diff

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