dbcool, envsys, powerd shutting down my machine

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I don't know whether this is a userland or kernel issue or a layer 8 problem.

After running a customized kernel, I found a server powered down.
The culprit turned out to be dbcool->envsys->powerd fabulating some temperature 
rose above limits.

envstat -d dbcool0 says:
           Current  CritMax  WarnMax  WarnMin  CritMin  Unit
[...]
r2_temp:    53.250   54.000                     45.000 degC
[...]

sysctl hw.dbcool0 says:
[...]
hw.dbcool0.r2_temp.Tmin = 44
hw.dbcool0.r2_temp.Ttherm = 57
hw.dbcool0.r2_temp.Thyst = 2

If I read that correctly, it means that at 54 degC, it's time for emergency 
shut-down, while only at 57 degC, fans have to run at full speed.
(Also, it seems to be threatning the hardware if that temp falls below 45.)

I have no clue where that magic value of 54 degC comes from. It's not in any 
config file I can find, I don't find such a value in sys/dev/i2c/dbcool.c. 
Is it the BIOS writing that value into the IC? Is it a chip manufacturer 
default?

The board is a Tyan S2882-D, in case that matters.
(Btw., does anyone know what r2_temp on that board is?)

I turned off powerd for now.

Thanks for any hints.