hwmon: (w83781d) Additional information about AS99127F PWM

This information was provided in lm-sensors ticket #2350:
http://www.lm-sensors.org/ticket/2350

This is IMHO still not enough to be able to safely implement fan
control support for the AS99127F, but this is valuable information so
I am adding it to the documentation.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/hwmon/w83781d

@@ -353,7 +353,7 @@ in6=255
 
 # PWM
 
-Additional info about PWM on the AS99127F (may apply to other Asus
+* Additional info about PWM on the AS99127F (may apply to other Asus
 chips as well) by Jean Delvare as of 2004-04-09:
 
 AS99127F revision 2 seems to have two PWM registers at 0x59 and 0x5A,
@@ -396,7 +396,7 @@ Please contact us if you can figure out how it is supposed to work. As
 long as we don't know more, the w83781d driver doesn't handle PWM on
 AS99127F chips at all.
 
-Additional info about PWM on the AS99127F rev.1 by Hector Martin:
+* Additional info about PWM on the AS99127F rev.1 by Hector Martin:
 
 I've been fiddling around with the (in)famous 0x59 register and
 found out the following values do work as a form of coarse pwm:
@@ -418,3 +418,36 @@ change.
 My mobo is an ASUS A7V266-E. This behavior is similar to what I got
 with speedfan under Windows, where 0-15% would be off, 15-2x% (can't
 remember the exact value) would be 70% and higher would be full on.
+
+* Additional info about PWM on the AS99127F rev.1 from lm-sensors
+  ticket #2350:
+
+I conducted some experiment on Asus P3B-F motherboard with AS99127F
+(Ver. 1).
+
+I confirm that 0x59 register control the CPU_Fan Header on this
+motherboard, and 0x5a register control PWR_Fan.
+
+In order to reduce the dependency of specific fan, the measurement is
+conducted with a digital scope without fan connected. I found out that
+P3B-F actually output variable DC voltage on fan header center pin,
+looks like PWM is filtered on this motherboard.
+
+Here are some of measurements:
+
+0x80     20 mV
+0x81     20 mV
+0x82    232 mV
+0x83   1.2  V
+0x84   2.31 V
+0x85   3.44 V
+0x86   4.62 V
+0x87   5.81 V
+0x88   7.01 V
+9x89   8.22 V
+0x8a   9.42 V
+0x8b  10.6  V
+0x8c  11.9  V
+0x8d  12.4  V
+0x8e  12.4  V
+0x8f  12.4  V