Kernel driver bh1770glc
  =======================
  
  Supported chips:
  ROHM BH1770GLC
  OSRAM SFH7770
  
  Data sheet:
  Not freely available
  
  Author:
  Samu Onkalo <samu.p.onkalo@nokia.com>
  
  Description
  -----------
  BH1770GLC and SFH7770 are combined ambient light and proximity sensors.
  ALS and proximity parts operates on their own, but they shares common I2C
  interface and interrupt logic. In principle they can run on their own,
  but ALS side results are used to estimate reliability of the proximity sensor.
  
  ALS produces 16 bit lux values. The chip contains interrupt logic to produce
  low and high threshold interrupts.
  
  Proximity part contains IR-led driver up to 3 IR leds. The chip measures
  amount of reflected IR light and produces proximity result. Resolution is
  8 bit. Driver supports only one channel. Driver uses ALS results to estimate
  reliability of the proximity results. Thus ALS is always running while
  proximity detection is needed.
  
  Driver uses threshold interrupts to avoid need for polling the values.
  Proximity low interrupt doesn't exists in the chip. This is simulated
  by using a delayed work. As long as there is proximity threshold above
  interrupts the delayed work is pushed forward. So, when proximity level goes
  below the threshold value, there is no interrupt and the delayed work will
  finally run. This is handled as no proximity indication.
  
  Chip state is controlled via runtime pm framework when enabled in config.
  
  Calibscale factor is used to hide differences between the chips. By default
  value set to neutral state meaning factor of 1.00. To get proper values,
  calibrated source of light is needed as a reference. Calibscale factor is set
  so that measurement produces about the expected lux value.
  
  SYSFS
  -----
  
  chip_id
  	RO - shows detected chip type and version
  
  power_state
  	RW - enable / disable chip. Uses counting logic
  	     1 enables the chip
  	     0 disables the chip
  
  lux0_input
  	RO - measured lux value
  	     sysfs_notify called when threshold interrupt occurs
  
  lux0_sensor_range
  	RO - lux0_input max value
  
  lux0_rate
  	RW - measurement rate in Hz
  
  lux0_rate_avail
  	RO - supported measurement rates
  
  lux0_thresh_above_value
  	RW - HI level threshold value. All results above the value
  	     trigs an interrupt. 65535 (i.e. sensor_range) disables the above
  	     interrupt.
  
  lux0_thresh_below_value
  	RW - LO level threshold value. All results below the value
  	     trigs an interrupt. 0 disables the below interrupt.
  
  lux0_calibscale
  	RW - calibration value. Set to neutral value by default.
  	     Output results are multiplied with calibscale / calibscale_default
  	     value.
  
  lux0_calibscale_default
  	RO - neutral calibration value
  
  prox0_raw
  	RO - measured proximity value
  	     sysfs_notify called when threshold interrupt occurs
  
  prox0_sensor_range
  	RO - prox0_raw max value
  
  prox0_raw_en
  	RW - enable / disable proximity - uses counting logic
  	     1 enables the proximity
  	     0 disables the proximity
  
  prox0_thresh_above_count
  	RW - number of proximity interrupts needed before triggering the event
  
  prox0_rate_above
  	RW - Measurement rate (in Hz) when the level is above threshold
  	     i.e. when proximity on has been reported.
  
  prox0_rate_below
  	RW - Measurement rate (in Hz) when the level is below threshold
  	     i.e. when proximity off has been reported.
  
  prox0_rate_avail
  	RO - Supported proximity measurement rates in Hz
  
  prox0_thresh_above0_value
  	RW - threshold level which trigs proximity events.
  	     Filtered by persistence filter (prox0_thresh_above_count)
  
  prox0_thresh_above1_value
  	RW - threshold level which trigs event immediately