Kernel driver lm93
  ==================
  
  Supported chips:
    * National Semiconductor LM93
      Prefix 'lm93'
      Addresses scanned: I2C 0x2c-0x2e
      Datasheet: http://www.national.com/ds.cgi/LM/LM93.pdf
    * National Semiconductor LM94
      Prefix 'lm94'
      Addresses scanned: I2C 0x2c-0x2e
      Datasheet: http://www.national.com/ds.cgi/LM/LM94.pdf
  
  Authors:
  	Mark M. Hoffman <mhoffman@lightlink.com>
  	Ported to 2.6 by Eric J. Bowersox <ericb@aspsys.com>
  	Adapted to 2.6.20 by Carsten Emde <ce@osadl.org>
  	Modified for mainline integration by Hans J. Koch <hjk@hansjkoch.de>
  
  Module Parameters
  -----------------
  
  * init: integer
    Set to non-zero to force some initializations (default is 0).
  * disable_block: integer
    A "0" allows SMBus block data transactions if the host supports them.  A "1"
    disables SMBus block data transactions.  The default is 0.
  * vccp_limit_type: integer array (2)
    Configures in7 and in8 limit type, where 0 means absolute and non-zero
    means relative.  "Relative" here refers to "Dynamic Vccp Monitoring using
    VID" from the datasheet.  It greatly simplifies the interface to allow
    only one set of limits (absolute or relative) to be in operation at a
    time (even though the hardware is capable of enabling both).  There's
    not a compelling use case for enabling both at once, anyway.  The default
    is "0,0".
  * vid_agtl: integer
    A "0" configures the VID pins for V(ih) = 2.1V min, V(il) = 0.8V max.
    A "1" configures the VID pins for V(ih) = 0.8V min, V(il) = 0.4V max.
    (The latter setting is referred to as AGTL+ Compatible in the datasheet.)
    I.e. this parameter controls the VID pin input thresholds; if your VID
    inputs are not working, try changing this.  The default value is "0".
  
  
  Hardware Description
  --------------------
  
  (from the datasheet)
  
  The LM93 hardware monitor has a two wire digital interface compatible with
  SMBus 2.0. Using an 8-bit ADC, the LM93 measures the temperature of two remote
  diode connected transistors as well as its own die and 16 power supply
  voltages. To set fan speed, the LM93 has two PWM outputs that are each
  controlled by up to four temperature zones. The fancontrol algorithm is lookup
  table based. The LM93 includes a digital filter that can be invoked to smooth
  temperature readings for better control of fan speed. The LM93 has four
  tachometer inputs to measure fan speed. Limit and status registers for all
  measured values are included. The LM93 builds upon the functionality of
  previous motherboard management ASICs and uses some of the LM85's features
  (i.e. smart tachometer mode). It also adds measurement and control support
  for dynamic Vccp monitoring and PROCHOT. It is designed to monitor a dual
  processor Xeon class motherboard with a minimum of external components.
  
  LM94 is also supported in LM93 compatible mode. Extra sensors and features of
  LM94 are not supported.
  
  
  User Interface
  --------------
  
  #PROCHOT:
  
  The LM93 can monitor two #PROCHOT signals.  The results are found in the
  sysfs files prochot1, prochot2, prochot1_avg, prochot2_avg, prochot1_max,
  and prochot2_max.  prochot1_max and prochot2_max contain the user limits
  for #PROCHOT1 and #PROCHOT2, respectively.  prochot1 and prochot2 contain
  the current readings for the most recent complete time interval.  The
  value of prochot1_avg and prochot2_avg is something like a 2 period
  exponential moving average (but not quite - check the datasheet). Note
  that this third value is calculated by the chip itself.  All values range
  from 0-255 where 0 indicates no throttling, and 255 indicates > 99.6%.
  
  The monitoring intervals for the two #PROCHOT signals is also configurable.
  These intervals can be found in the sysfs files prochot1_interval and
  prochot2_interval.  The values in these files specify the intervals for
  #P1_PROCHOT and #P2_PROCHOT, respectively.  Selecting a value not in this
  list will cause the driver to use the next largest interval.  The available
  intervals are (in seconds):
  
  #PROCHOT intervals: 0.73, 1.46, 2.9, 5.8, 11.7, 23.3, 46.6, 93.2, 186, 372
  
  It is possible to configure the LM93 to logically short the two #PROCHOT
  signals.  I.e. when #P1_PROCHOT is asserted, the LM93 will automatically
  assert #P2_PROCHOT, and vice-versa.  This mode is enabled by writing a
  non-zero integer to the sysfs file prochot_short.
  
  The LM93 can also override the #PROCHOT pins by driving a PWM signal onto
  one or both of them.  When overridden, the signal has a period of 3.56 ms,
  a minimum pulse width of 5 clocks (at 22.5kHz => 6.25% duty cycle), and
  a maximum pulse width of 80 clocks (at 22.5kHz => 99.88% duty cycle).
  
  The sysfs files prochot1_override and prochot2_override contain boolean
  integers which enable or disable the override function for #P1_PROCHOT and
  #P2_PROCHOT, respectively.  The sysfs file prochot_override_duty_cycle
  contains a value controlling the duty cycle for the PWM signal used when
  the override function is enabled.  This value ranges from 0 to 15, with 0
  indicating minimum duty cycle and 15 indicating maximum.
  
  #VRD_HOT:
  
  The LM93 can monitor two #VRD_HOT signals. The results are found in the
  sysfs files vrdhot1 and vrdhot2. There is one value per file: a boolean for
  which 1 indicates #VRD_HOT is asserted and 0 indicates it is negated. These
  files are read-only.
  
  Smart Tach Mode:
  
  (from the datasheet)
  
  	If a fan is driven using a low-side drive PWM, the tachometer
  	output of the fan is corrupted. The LM93 includes smart tachometer
  	circuitry that allows an accurate tachometer reading to be
  	achieved despite the signal corruption.  In smart tach mode all
  	four signals are measured within 4 seconds.
  
  Smart tach mode is enabled by the driver by writing 1 or 2 (associating the
  the fan tachometer with a pwm) to the sysfs file fan<n>_smart_tach.  A zero
  will disable the function for that fan.  Note that Smart tach mode cannot be
  enabled if the PWM output frequency is 22500 Hz (see below).
  
  Manual PWM:
  
  The LM93 has a fixed or override mode for the two PWM outputs (although, there
  are still some conditions that will override even this mode - see section
  15.10.6 of the datasheet for details.)  The sysfs files pwm1_override
  and pwm2_override are used to enable this mode; each is a boolean integer
  where 0 disables and 1 enables the manual control mode.  The sysfs files pwm1
  and pwm2 are used to set the manual duty cycle; each is an integer (0-255)
  where 0 is 0% duty cycle, and 255 is 100%.  Note that the duty cycle values
  are constrained by the hardware. Selecting a value which is not available
  will cause the driver to use the next largest value.  Also note: when manual
  PWM mode is disabled, the value of pwm1 and pwm2 indicates the current duty
  cycle chosen by the h/w.
  
  PWM Output Frequency:
  
  The LM93 supports several different frequencies for the PWM output channels.
  The sysfs files pwm1_freq and pwm2_freq are used to select the frequency. The
  frequency values are constrained by the hardware.  Selecting a value which is
  not available will cause the driver to use the next largest value.  Also note
  that this parameter has implications for the Smart Tach Mode (see above).
  
  PWM Output Frequencies (in Hz): 12, 36, 48, 60, 72, 84, 96, 22500 (default)
  
  Automatic PWM:
  
  The LM93 is capable of complex automatic fan control, with many different
  points of configuration.  To start, each PWM output can be bound to any
  combination of eight control sources.  The final PWM is the largest of all
  individual control sources to which the PWM output is bound.
  
  The eight control sources are: temp1-temp4 (aka "zones" in the datasheet),
  #PROCHOT 1 & 2, and #VRDHOT 1 & 2.  The bindings are expressed as a bitmask
  in the sysfs files pwm<n>_auto_channels, where a "1" enables the binding, and
  a "0" disables it. The h/w default is 0x0f (all temperatures bound).
  
  	0x01 - Temp 1
  	0x02 - Temp 2
  	0x04 - Temp 3
  	0x08 - Temp 4
  	0x10 - #PROCHOT 1
  	0x20 - #PROCHOT 2
  	0x40 - #VRDHOT 1
  	0x80 - #VRDHOT 2
  
  The function y = f(x) takes a source temperature x to a PWM output y.  This
  function of the LM93 is derived from a base temperature and a table of 12
  temperature offsets.  The base temperature is expressed in degrees C in the
  sysfs files temp<n>_auto_base.  The offsets are expressed in cumulative
  degrees C, with the value of offset <i> for temperature value <n> being
  contained in the file temp<n>_auto_offset<i>.  E.g. if the base temperature
  is 40C:
  
       offset #	temp<n>_auto_offset<i>	range		pwm
  	 1		0		-		 25.00%
  	 2		0		-		 28.57%
  	 3		1		40C - 41C	 32.14%
  	 4		1		41C - 42C	 35.71%
  	 5		2		42C - 44C	 39.29%
  	 6		2		44C - 46C	 42.86%
  	 7		2		48C - 50C	 46.43%
  	 8		2		50C - 52C	 50.00%
  	 9		2		52C - 54C	 53.57%
  	10		2		54C - 56C	 57.14%
  	11		2		56C - 58C	 71.43%
  	12		2		58C - 60C	 85.71%
  					> 60C		100.00%
  
  Valid offsets are in the range 0C <= x <= 7.5C in 0.5C increments.
  
  There is an independent base temperature for each temperature channel. Note,
  however, there are only two tables of offsets: one each for temp[12] and
  temp[34].  Therefore, any change to e.g. temp1_auto_offset<i> will also
  affect temp2_auto_offset<i>.
  
  The LM93 can also apply hysteresis to the offset table, to prevent unwanted
  oscillation between two steps in the offsets table.  These values are found in
  the sysfs files temp<n>_auto_offset_hyst.  The value in this file has the
  same representation as in temp<n>_auto_offset<i>.
  
  If a temperature reading falls below the base value for that channel, the LM93
  will use the minimum PWM value.  These values are found in the sysfs files
  temp<n>_auto_pwm_min.  Note, there are only two minimums: one each for temp[12]
  and temp[34].  Therefore, any change to e.g. temp1_auto_pwm_min will also
  affect temp2_auto_pwm_min.
  
  PWM Spin-Up Cycle:
  
  A spin-up cycle occurs when a PWM output is commanded from 0% duty cycle to
  some value > 0%.  The LM93 supports a minimum duty cycle during spin-up.  These
  values are found in the sysfs files pwm<n>_auto_spinup_min. The value in this
  file has the same representation as other PWM duty cycle values. The
  duration of the spin-up cycle is also configurable.  These values are found in
  the sysfs files pwm<n>_auto_spinup_time. The value in this file is
  the spin-up time in seconds.  The available spin-up times are constrained by
  the hardware.  Selecting a value which is not available will cause the driver
  to use the next largest value.
  
  Spin-up Durations: 0 (disabled, h/w default), 0.1, 0.25, 0.4, 0.7, 1.0,
  		   2.0, 4.0
  
  #PROCHOT and #VRDHOT PWM Ramping:
  
  If the #PROCHOT or #VRDHOT signals are asserted while bound to a PWM output
  channel, the LM93 will ramp the PWM output up to 100% duty cycle in discrete
  steps. The duration of each step is configurable. There are two files, with
  one value each in seconds: pwm_auto_prochot_ramp and pwm_auto_vrdhot_ramp.
  The available ramp times are constrained by the hardware.  Selecting a value
  which is not available will cause the driver to use the next largest value.
  
  Ramp Times: 0 (disabled, h/w default) to 0.75 in 0.05 second intervals
  
  Fan Boost:
  
  For each temperature channel, there is a boost temperature: if the channel
  exceeds this limit, the LM93 will immediately drive both PWM outputs to 100%.
  This limit is expressed in degrees C in the sysfs files temp<n>_auto_boost.
  There is also a hysteresis temperature for this function: after the boost
  limit is reached, the temperature channel must drop below this value before
  the boost function is disabled.  This temperature is also expressed in degrees
  C in the sysfs files temp<n>_auto_boost_hyst.
  
  GPIO Pins:
  
  The LM93 can monitor the logic level of four dedicated GPIO pins as well as the
  four tach input pins.  GPIO0-GPIO3 correspond to (fan) tach 1-4, respectively.
  All eight GPIOs are read by reading the bitmask in the sysfs file gpio.  The
  LSB is GPIO0, and the MSB is GPIO7.
  
  
  LM93 Unique sysfs Files
  -----------------------
  
  	file			description
  	-------------------------------------------------------------
  
  	prochot<n>		current #PROCHOT %
  
  	prochot<n>_avg		moving average #PROCHOT %
  
  	prochot<n>_max		limit #PROCHOT %
  
  	prochot_short		enable or disable logical #PROCHOT pin short
  
  	prochot<n>_override	force #PROCHOT assertion as PWM
  
  	prochot_override_duty_cycle
  				duty cycle for the PWM signal used when
  				#PROCHOT is overridden
  
  	prochot<n>_interval	#PROCHOT PWM sampling interval
  
  	vrdhot<n>		0 means negated, 1 means asserted
  
  	fan<n>_smart_tach	enable or disable smart tach mode
  
  	pwm<n>_auto_channels	select control sources for PWM outputs
  
  	pwm<n>_auto_spinup_min	minimum duty cycle during spin-up
  
  	pwm<n>_auto_spinup_time	duration of spin-up
  
  	pwm_auto_prochot_ramp	ramp time per step when #PROCHOT asserted
  
  	pwm_auto_vrdhot_ramp	ramp time per step when #VRDHOT asserted
  
  	temp<n>_auto_base	temperature channel base
  
  	temp<n>_auto_offset[1-12]
  				temperature channel offsets
  
  	temp<n>_auto_offset_hyst
  				temperature channel offset hysteresis
  
  	temp<n>_auto_boost	temperature channel boost (PWMs to 100%) limit
  
  	temp<n>_auto_boost_hyst	temperature channel boost hysteresis
  
  	gpio			input state of 8 GPIO pins; read-only