1 files changed, 24 insertions, 3 deletions

diff --git a/Documentation/hwmon/pc87427 b/Documentation/hwmon/pc87427
index db5cc1227a83..8fdd08c9e48b 100644
--- a/Documentation/hwmon/pc87427
+++ b/Documentation/hwmon/pc87427
@@ -18,10 +18,11 @@ Description
 
 The National Semiconductor Super I/O chip includes complete hardware
 monitoring capabilities. It can monitor up to 18 voltages, 8 fans and
-6 temperature sensors. Only the fans are supported at the moment.
+6 temperature sensors. Only the fans and temperatures are supported at
+the moment, voltages aren't.
 
-This chip also has fan controlling features, which are not yet supported
-by this driver either.
+This chip also has fan controlling features (up to 4 PWM outputs),
+which are partly supported by this driver.
 
 The driver assumes that no more than one chip is present, which seems
 reasonable.
@@ -36,3 +37,23 @@ signal. Speeds down to 83 RPM can be measured.
 An alarm is triggered if the rotation speed drops below a programmable
 limit. Another alarm is triggered if the speed is too low to be measured
 (including stalled or missing fan).
+
+
+Fan Speed Control
+-----------------
+
+Fan speed can be controlled by PWM outputs. There are 4 possible modes:
+always off, always on, manual and automatic. The latter isn't supported
+by the driver: you can only return to that mode if it was the original
+setting, and the configuration interface is missing.
+
+
+Temperature Monitoring
+----------------------
+
+The PC87427 relies on external sensors (following the SensorPath
+standard), so the resolution and range depend on the type of sensor
+connected. The integer part can be 8-bit or 9-bit, and can be signed or
+not. I couldn't find a way to figure out the external sensor data
+temperature format, so user-space adjustment (typically by a factor 2)
+may be required.