Kernel driver lm77
  ==================
  
  Supported chips:
    * National Semiconductor LM77
      Prefix: 'lm77'
      Addresses scanned: I2C 0x48 - 0x4b
      Datasheet: Publicly available at the National Semiconductor website
                 http://www.national.com/
  
  Author: Andras BALI <drewie@freemail.hu>
  
  Description
  -----------
  
  The LM77 implements one temperature sensor. The temperature
  sensor incorporates a band-gap type temperature sensor,
  10-bit ADC, and a digital comparator with user-programmable upper
  and lower limit values.

  The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
  critical (temp1_crit.) It also implements an hysteresis mechanism which
  applies to all 3 limits. The relative difference is stored in a single
  register on the chip, which means that the relative difference between
  the limit and its hysteresis is always the same for all 3 limits.
  
  This implementation detail implies the following:
  * When setting a limit, its hysteresis will automatically follow, the
    difference staying unchanged. For example, if the old critical limit
    was 80 degrees C, and the hysteresis was 75 degrees C, and you change
    the critical limit to 90 degrees C, then the hysteresis will
    automatically change to 85 degrees C.
  * All 3 hysteresis can't be set independently. We decided to make
    temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
    read-only. Setting temp1_crit_hyst writes the difference between
    temp1_crit_hyst and temp1_crit into the chip, and the same relative
    hysteresis applies automatically to the low and high limits.
  * The limits should be set before the hysteresis.