adt7470: make automatic fan control really work

It turns out that the adt7470's automatic fan control algorithm only works
when the temperature sensors get updated.  This in turn happens only when
someone tells the chip to read its temperature sensors.  Regrettably, this
means that we have to drive the chip periodically.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 11 deletions

diff --git a/Documentation/hwmon/adt7470 b/Documentation/hwmon/adt7470
index 75d13ca147cc..8ce4aa0a0f55 100644
--- a/Documentation/hwmon/adt7470
+++ b/Documentation/hwmon/adt7470
@@ -31,15 +31,11 @@ Each of the measured inputs (temperature, fan speed) has corresponding high/low
 limit values. The ADT7470 will signal an ALARM if any measured value exceeds
 either limit.
 
-The ADT7470 DOES NOT sample all inputs continuously.  A single pin on the
-ADT7470 is connected to a multitude of thermal diodes, but the chip must be
-instructed explicitly to read the multitude of diodes.  If you want to use
-automatic fan control mode, you must manually read any of the temperature
-sensors or the fan control algorithm will not run.  The chip WILL NOT DO THIS
-AUTOMATICALLY; this must be done from userspace.  This may be a bug in the chip
-design, given that many other AD chips take care of this.  The driver will not
-read the registers more often than once every 5 seconds.  Further,
-configuration data is only read once per minute.
+The ADT7470 samples all inputs continuously.  A kernel thread is started up for
+the purpose of periodically querying the temperature sensors, thus allowing the
+automatic fan pwm control to set the fan speed.  The driver will not read the
+registers more often than once every 5 seconds.  Further, configuration data is
+only read once per minute.
 
 Special Features
 ----------------
@@ -72,5 +68,6 @@ pwm#_auto_point2_temp.
 Notes
 -----
 
-As stated above, the temperature inputs must be read periodically from
-userspace in order for the automatic pwm algorithm to run.
+The temperature inputs no longer need to be read periodically from userspace in
+order for the automatic pwm algorithm to run.  This was the case for earlier
+versions of the driver.