hwmon/it87: Add PWM base frequency control

Let the user select the base PWM frequency when using the it87
hardware monitoring driver. Different frequencies can give better
control on some fans.

Also update the documentation to mention the PWM frequency control
files, with misc cleanups to the PWM section.

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

2 files changed, 20 insertions, 5 deletions

diff --git a/Documentation/hwmon/it87 b/Documentation/hwmon/it87
index 74a80992d237..c0528d6f9ace 100644
--- a/Documentation/hwmon/it87
+++ b/Documentation/hwmon/it87
@@ -135,6 +135,16 @@ Give 0 for unused sensor. Any other value is invalid. To configure this at
 startup, consult lm_sensors's /etc/sensors.conf. (2 = thermistor;
 3 = thermal diode)
 
+
+Fan speed control
+-----------------
+
 The fan speed control features are limited to manual PWM mode. Automatic
 "Smart Guardian" mode control handling is not implemented. However
 if you want to go for "manual mode" just write 1 to pwmN_enable.
+
+If you are only able to control the fan speed with very small PWM values,
+try lowering the PWM base frequency (pwm1_freq). Depending on the fan,
+it may give you a somewhat greater control range. The same frequency is
+used to drive all fan outputs, which is why pwm2_freq and pwm3_freq are
+read-only.
diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface
index efef3b962cd3..d73d2e8c7534 100644
--- a/Documentation/hwmon/sysfs-interface
+++ b/Documentation/hwmon/sysfs-interface
@@ -166,16 +166,21 @@ pwm[1-*]	Pulse width modulation fan control.
 
 pwm[1-*]_enable
                 Switch PWM on and off.
-                Not always present even if fan*_pwm is.
+                Not always present even if pwmN is.
                 0: turn off
                 1: turn on in manual mode
                 2+: turn on in automatic mode
-                Check individual chip documentation files for automatic mode details.
+                Check individual chip documentation files for automatic mode
+                details.
                 RW
 
-pwm[1-*]_mode
-                0: DC mode
-                1: PWM mode
+pwm[1-*]_mode   0: DC mode (direct current)
+                1: PWM mode (pulse-width modulation)
+                RW
+
+pwm[1-*]_freq   Base PWM frequency in Hz.
+                Only possibly available when pwmN_mode is PWM, but not always
+                present even then.
                 RW
 
 pwm[1-*]_auto_channels_temp