hwmon: Driver for NTC Thermistors

Add support for NTC Thermistor series. In this release, the
following thermistors are supported: NCP15WB473, NCP18WB473, NCP03WB473,
and NCP15WL333. This driver is based on the datasheet of MURATA.

The driver in the patch does conversion from the raw ADC value
(either voltage or resistence) to temperature. In order to use
voltage values as input, the circuit schematics should be provided
with the platform data. A compensation table for each type of thermistor
is provided for the conversion.

Signed-off-by: Donggeun Kim <dg77.kim@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: KyungMin Park <kyungmin.park@samsung.com>
Reviewed-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

1 files changed, 93 insertions, 0 deletions

diff --git a/Documentation/hwmon/ntc_thermistor b/Documentation/hwmon/ntc_thermistor
new file mode 100644
index 0000000..3bfda94
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+Kernel driver ntc_thermistor
+=================
+
+Supported thermistors:
+* Murata NTC Thermistors NCP15WB473, NCP18WB473, NCP21WB473, NCP03WB473, NCP15WL333
+  Prefixes: 'ncp15wb473', 'ncp18wb473', 'ncp21wb473', 'ncp03wb473', 'ncp15wl333'
+  Datasheet: Publicly available at Murata
+
+Other NTC thermistors can be supported simply by adding compensation
+tables; e.g., NCP15WL333 support is added by the table ncpXXwl333.
+
+Authors:
+	MyungJoo Ham <myungjoo.ham@samsung.com>
+
+Description
+-----------
+
+The NTC thermistor is a simple thermistor that requires users to provide the
+resistance and lookup the corresponding compensation table to get the
+temperature input.
+
+The NTC driver provides lookup tables with a linear approximation function
+and four circuit models with an option not to use any of the four models.
+
+The four circuit models provided are:
+
+	$: resister, [TH]: the thermistor
+
+ 1. connect = NTC_CONNECTED_POSITIVE, pullup_ohm > 0
+
+   [pullup_uV]
+       |    |
+      [TH]  $ (pullup_ohm)
+       |    |
+       +----+-----------------------[read_uV]
+       |
+       $ (pulldown_ohm)
+       |
+      --- (ground)
+
+ 2. connect = NTC_CONNECTED_POSITIVE, pullup_ohm = 0 (not-connected)
+
+   [pullup_uV]
+       |
+      [TH]
+       |
+       +----------------------------[read_uV]
+       |
+       $ (pulldown_ohm)
+       |
+      --- (ground)
+
+ 3. connect = NTC_CONNECTED_GROUND, pulldown_ohm > 0
+
+   [pullup_uV]
+       |
+       $ (pullup_ohm)
+       |
+       +----+-----------------------[read_uV]
+       |    |
+      [TH]  $ (pulldown_ohm)
+       |    |
+      -------- (ground)
+
+ 4. connect = NTC_CONNECTED_GROUND, pulldown_ohm = 0 (not-connected)
+
+   [pullup_uV]
+       |
+       $ (pullup_ohm)
+       |
+       +----------------------------[read_uV]
+       |
+      [TH]
+       |
+      --- (ground)
+
+When one of the four circuit models is used, read_uV, pullup_uV, pullup_ohm,
+pulldown_ohm, and connect should be provided. When none of the four models
+are suitable or the user can get the resistance directly, the user should
+provide read_ohm and _not_ provide the others.
+
+Sysfs Interface
+---------------
+name		the mandatory global attribute, the thermistor name.
+
+temp1_type	always 4 (thermistor)
+		RO
+
+temp1_input	measure the temperature and provide the measured value.
+		(reading this file initiates the reading procedure.)
+		RO
+
+Note that each NTC thermistor has only _one_ thermistor; thus, only temp1 exists.