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authorJean Delvare <khali@linux-fr.org>2010-03-05 22:17:21 +0100
committerJean Delvare <khali@linux-fr.org>2010-03-05 22:17:21 +0100
commit4f3f51bc21d434f8d91a79438a1957ec0baa9e30 (patch)
treeb61b17498c2b3a46377692526f56551681d1894d /Documentation
parent404a552d8ae6847ae17f3c749bd5d312da08efe4 (diff)
hwmon: (it87) Add support for old automatic fan speed control
Add support for the automatic fan speed control interface as implemented by IT8705F chips up to revision F and IT8712F chips up to revision G. This implementation fits very well in our standard sysfs interface. I implemented the old and not the new interface because the only chip I have at hand is an old one, and the new interface is more difficult to map to the standard sysfs interface. Adding support later should be possible though, if someone with a supported chip is interested. Signed-off-by: Jean Delvare <khali@linux-fr.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/hwmon/it8727
1 files changed, 25 insertions, 2 deletions
diff --git a/Documentation/hwmon/it87 b/Documentation/hwmon/it87
index a96a70fe802..0083bd31735 100644
--- a/Documentation/hwmon/it87
+++ b/Documentation/hwmon/it87
@@ -146,11 +146,34 @@ 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.
+"Smart Guardian" mode control handling is only implemented for older chips
+(see below.) 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.
+
+
+Automatic fan speed control (old interface)
+-------------------------------------------
+
+The driver supports the old interface to automatic fan speed control
+which is implemented by IT8705F chips up to revision F and IT8712F
+chips up to revision G.
+
+This interface implements 4 temperature vs. PWM output trip points.
+The PWM output of trip point 4 is always the maximum value (fan running
+at full speed) while the PWM output of the other 3 trip points can be
+freely chosen. The temperature of all 4 trip points can be freely chosen.
+Additionally, trip point 1 has an hysteresis temperature attached, to
+prevent fast switching between fan on and off.
+
+The chip automatically computes the PWM output value based on the input
+temperature, based on this simple rule: if the temperature value is
+between trip point N and trip point N+1 then the PWM output value is
+the one of trip point N. The automatic control mode is less flexible
+than the manual control mode, but it reacts faster, is more robust and
+doesn't use CPU cycles.