Use linear interpolation instead of quadratic to choose PWM values.

This is simpler and will work better in most cases. For example this
should address at least part of ticket #2224. It seems that quadratic
was used to lower the average noise level, but I don't think this is a
valid reason. The new MINPWM and MAXPWM parameters will also let the
user control the noise level if really needed.


git-svn-id: http://lm-sensors.org/svn/lm-sensors/branches/lm-sensors-3.0.0@4589 7894878c-1315-0410-8ee3-d5d059ff63e0

CHANGES

@@ -29,6 +29,7 @@ SVN HEAD
                       Check for configuration file validity
                       Support optional min and max PWM values
                       Better integration with init scripts
+                      Use linear control instead of quadratic
   Program pwmconfig: Use smaller steps for low PWM values
                      Support optional min and max PWM values
   Program rrd: Support only hwmon class devices

doc/fancontrol.txt

@@ -120,16 +120,14 @@ fancontrol first reads its configuration, writes it to arrays and loops its
 main function.  This function gets the temperatures and fanspeeds from
 kernel driver files and calculates new speeds depending on temperature
 changes, but only if the temp is between MINTEMP and MAXTEMP. After that, the
-new values are written to the pwm outputs.  Currently the speed increases
-quadratically with rising temperature. This way you won't hear your fans most
-of the time at best.
+new values are written to the pwm outputs.  The pwm value increases
+linearly with rising temperature.
 
 
 Planned features
 
 rc-scripts for some gnu/linux-distributions
 smoother regulation (temp interpolation)
-other curve styles (linear, exponential)
 gui for configuration
 
 If you have other wishes or want to contribute something, please let me know:

prog/pwm/fancontrol

@@ -324,7 +324,7 @@ function UpdateFanSpeeds {
 		  then pwmval=$maxpwm # over max temp, use defined max pwm
 		else 
 		  # calculate the new value from temperature and settings
-		  let pwmval="((${tval}-${mint})**2)*(${maxpwm}-${minso})/((${maxt}-${mint})**2)+${minso}"
+		  let pwmval="(${tval}-${mint})*(${maxpwm}-${minso})/(${maxt}-${mint})+${minso}"
 		  if [ $pwmpval -eq 0 -o $fanval -eq 0 ]
 		  then # if fan was stopped start it using a safe value
 		  	echo $minsa > $pwmo

prog/pwm/fancontrol.pl

@@ -390,7 +390,7 @@ sub UpdateFanSpeeds()
          { $pwmval = MAX; }
        else
          {
-           $pwmval = eval ( ($tval - $mint) / ($maxt - $mint) )**2 ;
+           $pwmval = eval ( ($tval - $mint) / ($maxt - $mint) );
            $pwmval *= (255 - $minso);
            $pwmval += $minso;
            $pwmval = int($pwmval);