hwmon: add driver for max31875

MAX31875 Low-Power I2C Temperature Sensor

Signed-off-by: John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>

Author: jemfgeronimo

Documentation/hwmon/index.rst

@@ -138,6 +138,7 @@ Hardware Monitoring Kernel Drivers
    max31785
    max31790
    max31827
+   max31875
    max34440
    max6620
    max6639

Documentation/hwmon/max31875.rst

@@ -0,0 +1,99 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver max31875
+======================
+
+Supported chips:
+
+  * Maxim MAX31875
+
+    Prefix: 'max31875'
+
+    Addresses scanned: I2C 0x48 - 0x4f
+
+    Datasheet: Publicly available at the Analog Devices website
+
+
+Authors:
+	- John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
+
+Description
+-----------
+
+MAX31875 implements a temperature sensor with a 4 WLP packaging scheme. This
+sensor measures the temperature of the chip itself.
+
+MAX31875 has an over temperature alarm with an effective value and a hysteresis
+value: +80 and +75 degrees.
+
+The alarm can be configured in comparator and interrupt mode from the
+devicetree. In Comparator mode, the OT status bit have a value of 1 when the
+temperature rises above the T_OS value, which is also subject to the Fault Queue
+selection. OT status returns to 0 when the temperature drops below the T_HYST
+value or when shutdown mode is entered.
+
+In interrupt mode exceeding T_OS also sets OT status to 1, which remains set
+until a read operation is performed on any of the registers; at this point, it
+returns to 0. Once OT status is set to 1 from exceeding T_OS and reset, it is
+set to 1 again only when the temperature drops below T_HYST. The output remains
+asserted until it is reset by a read. It is set again if the temperature rises
+above T_OS, and so on.
+
+Putting the MAX31875 into shutdown mode also resets the OT status. Note that if
+the mode is changed while OT status is set, an OT status reset may be required
+before it begins to behave normally. To prevent this, it is recommended to
+perform a read of the configuration/status register to clear the status bits
+before changing the operating mode.
+
+The conversions can be manual with the one-shot functionality and automatic with
+a set frequency. When powered on, the chip measures temperatures with 0.25
+conv/s. The conversion rate can be modified with update_interval attribute of
+the chip. Conversion/second = 1/update_interval. Thus, the available options
+according to the data sheet are:
+
+- 4000 (ms) = 0.25 conv/sec (default)
+- 1000 (ms) = 1 conv/sec
+- 250 (ms) = 4 conv/sec
+- 125 (ms) = 8 conv/sec
+
+Enabling the device when it is already enabled has the side effect of setting
+the conversion frequency to 0.25 conv/s. The conversion time varies depending on
+the resolution.
+
+The conversion time doubles with every bit of increased resolution. The
+available resolutions are:
+
+- 8 bit -> 8.75 ms conversion time
+- 9 bit -> 17.5 ms conversion time
+- 10 bit (default) -> 35 ms conversion time
+- 12 bit -> 140 ms conversion time
+- 13 bit (extended) -> 280 ms conversion time
+
+There is a temp1_resolution attribute which indicates the unit change in the
+input temperature in milli-degrees C. In extended format, the MSB is given a
+value of 128 degrees C (compared to normal format: 64 degrees C), which allows
+temperatures as high as 150 degrees C to be measured.
+
+- 1000 mC -> 8 bit
+- 500 mC -> 9 bit
+- 250 mC -> 10 bit (default)
+- 62 mC -> 12 bit - actually this is 62.5, but the file returns 62
+- 62 mC -> 13 bit (extended) - actually this is 62.5, but the file returns 62
+
+When chip is in shutdown mode and a read operation is requested, one-shot is
+triggered, the device waits for <conversion time> ms, and only after that is
+the temperature value register read. Note that the conversion times are rounded
+up to the nearest possible integer.
+
+The LSB of the temperature values is 0.0625 degrees Celsius, but the values of
+the temperatures are displayed in milli-degrees. This means, that some data is
+lost. The step between 2 consecutive values is 62 or 63. This effect can be seen
+in the writing of alarm values too. For positive numbers the user-input value
+will always be rounded down to the nearest possible value, for negative numbers
+the user-input will always be rounded up to the nearest possible value.
+
+Bus timeout resets the I2C-compatible interface when SCL is low for more than
+30ms (nominal).
+
+The Fault Queue bits select how many consecutive temperature faults must occur
+before overtemperature fault is indicated in the OT status bit.

MAINTAINERS

@@ -12602,6 +12602,8 @@ L:	linux-hwmon@vger.kernel.org
 S:	Supported
 W:	http://ez.analog.com/community/linux-device-drivers
 F:	Documentation/devicetree/bindings/hwmon/adi,max31875.yaml
+F:	Documentation/hwmon/max31875.rst
+F:	drivers/hwmon/max31875.c
 
 MAX31335 RTC DRIVER
 M:	Antoniu Miclaus <antoniu.miclaus@analog.com>

drivers/hwmon/Kconfig

@@ -1102,6 +1102,15 @@ config MAX31827
 	  This driver can also be built as a module.  If so, the module
 	  will be called max31827.
 
+config SENSORS_MAX31875
+	tristate "MAX31875 low-power I2C temperature sensor"
+	depends on I2C
+	help
+	  If you say yes here you get support for MAX31875 temperature sensor.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called max31875.
+
 config SENSORS_MAX6620
 	tristate "Maxim MAX6620 fan controller"
 	depends on I2C

drivers/hwmon/Makefile

@@ -150,6 +150,7 @@ obj-$(CONFIG_SENSORS_MAX6650)	+= max6650.o
 obj-$(CONFIG_SENSORS_MAX6697)	+= max6697.o
 obj-$(CONFIG_SENSORS_MAX31790)	+= max31790.o
 obj-$(CONFIG_MAX31827) += max31827.o
+obj-$(CONFIG_SENSORS_MAX31875)	+= max31875.o
 obj-$(CONFIG_SENSORS_MC13783_ADC)+= mc13783-adc.o
 obj-$(CONFIG_SENSORS_MCP3021)	+= mcp3021.o
 obj-$(CONFIG_SENSORS_TC654)	+= tc654.o