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>

5 files changed, 614 insertions, 0 deletions

diff --git a/Documentation/hwmon/ntc_thermistor b/Documentation/hwmon/ntc_thermistor
new file mode 100644
index 000000000000..3bfda94096fd
--- /dev/null
+++ b/Documentation/hwmon/ntc_thermistor
@@ -0,0 +1,93 @@
+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.
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index dec5eee3542f..770fc8195627 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -777,6 +777,20 @@ config SENSORS_MAX6650
           This driver can also be built as a module.  If so, the module
           will be called max6650.
 
+config SENSORS_NTC_THERMISTOR
+        tristate "NTC thermistor support"
+        depends on EXPERIMENTAL
+        help
+          This driver supports NTC thermistors sensor reading and its
+          interpretation. The driver can also monitor the temperature and
+          send notifications about the temperature.
+
+          Currently, this driver supports
+          NCP15WB473, NCP18WB473, NCP21WB473, NCP03WB473, and NCP15WL333.
+
+          This driver can also be built as a module.  If so, the module
+          will be called ntc-thermistor.
+
 config SENSORS_PC87360
         tristate "National Semiconductor PC87360 family"
         select HWMON_VID
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index a6d519e568c0..1b7dc770aa60 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -92,6 +92,7 @@ obj-$(CONFIG_SENSORS_MAX6639)	+= max6639.o
 obj-$(CONFIG_SENSORS_MAX6642)   += max6642.o
 obj-$(CONFIG_SENSORS_MAX6650)   += max6650.o
 obj-$(CONFIG_SENSORS_MC13783_ADC)+= mc13783-adc.o
+obj-$(CONFIG_SENSORS_NTC_THERMISTOR)    += ntc_thermistor.o
 obj-$(CONFIG_SENSORS_PC87360)   += pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)   += pc87427.o
 obj-$(CONFIG_SENSORS_PCF8591)   += pcf8591.o
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
new file mode 100644
index 000000000000..d7926f4336b5
--- /dev/null
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -0,0 +1,453 @@
+/*
+ * ntc_thermistor.c - NTC Thermistors
+ *
+ *  Copyright (C) 2010 Samsung Electronics
+ *  MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/pm_runtime.h>
+#include <linux/math64.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+
+#include <linux/platform_data/ntc_thermistor.h>
+
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+
+struct ntc_compensation {
+        int             temp_C;
+        unsigned int    ohm;
+};
+
+/*
+ * A compensation table should be sorted by the values of .ohm
+ * in descending order.
+ * The following compensation tables are from the specification of Murata NTC
+ * Thermistors Datasheet
+ */
+const struct ntc_compensation ncpXXwb473[] = {
+        { .temp_C       = -40, .ohm     = 1747920 },
+        { .temp_C       = -35, .ohm     = 1245428 },
+        { .temp_C       = -30, .ohm     = 898485 },
+        { .temp_C       = -25, .ohm     = 655802 },
+        { .temp_C       = -20, .ohm     = 483954 },
+        { .temp_C       = -15, .ohm     = 360850 },
+        { .temp_C       = -10, .ohm     = 271697 },