hwmon: Driver for Nuvoton NCT6775F, NCT6776F, and NCT6779D

This driver will replace the w83627ehf driver for NCT6775F and NCT6776F,
and provides support for NCT6779D.

This patch provides support for voltage monitor attributes.
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>

Documentation/hwmon/nct6775

+Note
+====
+
+This driver supersedes the NCT6775F and NCT6776F support in the W83627EHF
+driver.
+
+Kernel driver NCT6775
+=====================
+
+Supported chips:
+  * Nuvoton NCT6775F/W83667HG-I
+    Prefix: 'nct6775'
+    Addresses scanned: ISA address retrieved from Super I/O registers
+    Datasheet: Available from Nuvoton upon request
+  * Nuvoton NCT6776F
+    Prefix: 'nct6776'
+    Addresses scanned: ISA address retrieved from Super I/O registers
+    Datasheet: Available from Nuvoton upon request
+  * Nuvoton NCT6779D
+    Prefix: 'nct6779'
+    Addresses scanned: ISA address retrieved from Super I/O registers
+    Datasheet: Available from Nuvoton upon request
+
+Authors:
+        Guenter Roeck <linux@roeck-us.net>
+
+Description
+-----------
+
+This driver implements support for the Nuvoton NCT6775F, NCT6776F, and NCT6779D
+super I/O chips.
+
+The chips support up to 25 temperature monitoring sources. Up to 6 of those are
+direct temperature sensor inputs, the others are special sources such as PECI,
+PCH, and SMBUS. Depending on the chip type, 2 to 6 of the temperature sources
+can be monitored and compared against minimum, maximum, and critical
+temperatures. The driver reports up to 10 of the temperatures to the user.
+There are 4 to 5 fan rotation speed sensors, 8 to 15 analog voltage sensors,
+one VID, alarms with beep warnings (control unimplemented), and some automatic
+fan regulation strategies (plus manual fan control mode).
+
+The temperature sensor sources on all chips are configurable. The configured
+source for each of the temperature sensors is provided in tempX_label.
+
+Temperatures are measured in degrees Celsius and measurement resolution is
+either 1 degC or 0.5 degC, depending on the temperature source and
+configuration. An alarm is triggered when the temperature gets higher than
+the high limit; it stays on until the temperature falls below the hysteresis
+value. Alarms are only supported for temp1 to temp6, depending on the chip type.
+
+Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
+triggered if the rotation speed has dropped below a programmable limit. On
+NCT6775F, fan readings can be divided by a programmable divider (1, 2, 4, 8,
+16, 32, 64 or 128) to give the readings more range or accuracy; the other chips
+do not have a fan speed divider. The driver sets the most suitable fan divisor
+itself; specifically, it doubles the divider value each time a fan speed reading
+returns an invalid value. Some fans might not be present because they share pins
+with other functions.
+
+Voltage sensors (also known as IN sensors) report their values in millivolts.
+An alarm is triggered if the voltage has crossed a programmable minimum
+or maximum limit.
+
+The driver supports automatic fan control mode known as Thermal Cruise.
+In this mode, the chip attempts to keep the measured temperature in a
+predefined temperature range. If the temperature goes out of range, fan
+is driven slower/faster to reach the predefined range again.
+
+The mode works for fan1-fan5.
+
+Usage Notes
+-----------
+
+On various ASUS boards with NCT6776F, it appears that CPUTIN is not really
+connected to anything and floats, or that it is connected to some non-standard
+temperature measurement device. As a result, the temperature reported on CPUTIN
+will not reflect a usable value. It often reports unreasonably high
+temperatures, and in some cases the reported temperature declines if the actual
+temperature increases (similar to the raw PECI temperature value - see PECI
+specification for details). CPUTIN should therefore be be ignored on ASUS
+boards. The CPU temperature on ASUS boards is reported from PECI 0.

drivers/hwmon/Kconfig

@@ -897,6 +897,19 @@ config SENSORS_MCP3021
 	  This driver can also be built as a module.  If so, the module
 	  will be called mcp3021.
 
+config SENSORS_NCT6775
+	tristate "Nuvoton NCT6775F, NCT6776F, NCT6779D"
+	depends on !PPC
+	select HWMON_VID
+	help
+	  If you say yes here you get support for the hardware monitoring
+	  functionality of the Nuvoton NCT6775F, NCT6776F, and NCT6779D
+	  Super-I/O chips. This driver replaces the w83627ehf driver for
+	  NCT6775F and NCT6776F.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called nct6775.
+
 config SENSORS_NTC_THERMISTOR
 	tristate "NTC thermistor support"
 	depends on (!OF && !IIO) || (OF && IIO)

drivers/hwmon/Makefile

@@ -105,6 +105,7 @@ obj-$(CONFIG_SENSORS_MAX6650)	+= max6650.o
 obj-$(CONFIG_SENSORS_MAX6697)	+= max6697.o
 obj-$(CONFIG_SENSORS_MC13783_ADC)+= mc13783-adc.o
 obj-$(CONFIG_SENSORS_MCP3021)	+= mcp3021.o
+obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
 obj-$(CONFIG_SENSORS_NTC_THERMISTOR)	+= ntc_thermistor.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o