hwmon: Add driver for SMSC EMC2103 temperature monitor and fan controller

SMSC's EMC2103 family of temperature/fan controllers have 1
onboard and up to 3 external temperature sensors, and allow
closed-loop control of one fan.  This patch adds support for
them.

Signed-off-by: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/hwmon/emc2103

@@ -0,0 +1,33 @@
+Kernel driver emc2103
+======================
+
+Supported chips:
+  * SMSC EMC2103
+    Addresses scanned: I2C 0x2e
+    Prefix: 'emc2103'
+    Datasheet: Not public
+
+Authors:
+        Steve Glendinning <steve.glendinning@smsc.com>
+
+Description
+-----------
+
+The Standard Microsystems Corporation (SMSC) EMC2103 chips
+contain up to 4 temperature sensors and a single fan controller.
+
+Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
+triggered if the rotation speed has dropped below a programmable limit. Fan
+readings can be divided by a programmable divider (1, 2, 4 or 8) to give
+the readings more range or accuracy. Not all RPM values can accurately be
+represented, so some rounding is done. With a divider of 1, the lowest
+representable value is 480 RPM.
+
+This driver supports RPM based control, to use this a fan target
+should be written to fan1_target and pwm1_enable should be set to 3.
+
+The 2103-2 and 2103-4 variants have a third temperature sensor, which can
+be connected to two anti-parallel diodes.  These values can be read
+as temp3 and temp4.  If only one diode is attached to this channel, temp4
+will show as "fault".  The module parameter "apd=0" can be used to suppress
+this 4th channel when anti-parallel diodes are not fitted.