From fd9077bd03d1ea04a8208d76d9c61837d4d2a014 Mon Sep 17 00:00:00 2001
From: Jean Delvare <khali@linux-fr.org>
Date: Sun, 8 Jul 2007 10:01:50 +0000
Subject: [PATCH] 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/trunk@4588 7894878c-1315-0410-8ee3-d5d059ff63e0
---
 CHANGES                | 1 +
 doc/fancontrol.txt     | 6 ++----
 prog/pwm/fancontrol    | 2 +-
 prog/pwm/fancontrol.pl | 2 +-
 4 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/CHANGES b/CHANGES
index 645a6baa..0d5eb0e1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -31,6 +31,7 @@ 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 mkpatch: Include w83627ehf
diff --git a/doc/fancontrol.txt b/doc/fancontrol.txt
index 25f8afb1..eee5bf49 100644
--- a/doc/fancontrol.txt
+++ b/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:
diff --git a/prog/pwm/fancontrol b/prog/pwm/fancontrol
index 107da10a..448b3d47 100755
--- a/prog/pwm/fancontrol
+++ b/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
diff --git a/prog/pwm/fancontrol.pl b/prog/pwm/fancontrol.pl
index cb7327bc..fe7f68b4 100755
--- a/prog/pwm/fancontrol.pl
+++ b/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);