hwmon: WM831x PMIC hardware monitoring driver

This driver adds support for the hardware monitoring features of
the WM831x PMICs to the hwmon API. Monitoring is provided for
the system voltages supported natively by the WM831x, the chip
temperature, the battery temperature and the auxiliary inputs
of the WM831x.

Currently no alarms are supported, though digital comparators on
the WM831x devices would allow these to be provided.

Since the auxiliary and battery temperature input scaling depends
on the system configuration the value is reported as a voltage to
userspace.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/hwmon/wm831x b/Documentation/hwmon/wm831x
new file mode 100644
index 000000000000..24f47d8f6a42
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+Kernel driver wm831x-hwmon
+==========================
+
+Supported chips:
+  * Wolfson Microelectronics WM831x PMICs
+    Prefix: 'wm831x'
+    Datasheet:
+        http://www.wolfsonmicro.com/products/WM8310
+        http://www.wolfsonmicro.com/products/WM8311
+        http://www.wolfsonmicro.com/products/WM8312
+
+Authors: Mark Brown <broonie@opensource.wolfsonmicro.com>
+
+Description
+-----------
+
+The WM831x series of PMICs include an AUXADC which can be used to
+monitor a range of system operating parameters, including the voltages
+of the major supplies within the system.  Currently the driver provides
+reporting of all the input values but does not provide any alarms.
+
+Voltage Monitoring
+------------------
+
+Voltages are sampled by a 12 bit ADC.  Voltages in milivolts are 1.465
+times the ADC value.
+
+Temperature Monitoring
+----------------------
+
+Temperatures are sampled by a 12 bit ADC.  Chip and battery temperatures
+are available.  The chip temperature is calculated as:
+
+        Degrees celsius = (512.18 - data) / 1.0983
+
+while the battery temperature calculation will depend on the NTC
+thermistor component.