tda —
TDA8444 fan speed controller
tda0 at iic1 addr 0x24: fan-control
The tda driver provides support for the TDA8444 DAC used
  to control the fan speeds in Sun Blade 1000 and Blade 2000 systems. The speed
  of the CPU fan and of the system fan are automatically adjusted every 60
  seconds, based on the currently reported CPU and system temperatures,
  respectively.
The speed-related values are made available through the
    envstat(8) interface. The
    range of the values are:
The temperatures are reported as ‘internal’ and
  ‘external’ instead of ‘system’ and
  ‘CPU’, respectively.