hwmon: Add LTC2990 sensor driver

This adds support for the Linear Technology LTC2990  I2C System Monitor.
The LTC2990 supports a combination of voltage, current and temperature
monitoring. This driver currently only supports reading two currents
by measuring two differential voltages across series resistors, in
addition to the Vcc supply voltage and internal temperature.

This is sufficient to support the Topic Miami SOM which uses this chip
to monitor the currents flowing into the FPGA and the CPU parts.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/ltc2990

@@ -0,0 +1,43 @@
+Kernel driver ltc2990
+=====================
+
+Supported chips:
+  * Linear Technology LTC2990
+    Prefix: 'ltc2990'
+    Addresses scanned: -
+    Datasheet: http://www.linear.com/product/ltc2990
+
+Author: Mike Looijmans <mike.looijmans@topic.nl>
+
+
+Description
+-----------
+
+LTC2990 is a Quad I2C Voltage, Current and Temperature Monitor.
+The chip's inputs can measure 4 voltages, or two inputs together (1+2 and 3+4)
+can be combined to measure a differential voltage, which is typically used to
+measure current through a series resistor, or a temperature.
+
+This driver currently uses the 2x differential mode only. In order to support
+other modes, the driver will need to be expanded.
+
+
+Usage Notes
+-----------
+
+This driver does not probe for PMBus devices. You will have to instantiate
+devices explicitly.
+
+
+Sysfs attributes
+----------------
+
+The "curr*_input" measurements actually report the voltage drop across the
+input pins in microvolts. This is equivalent to the current through a 1mOhm
+sense resistor. Divide the reported value by the actual sense resistor value
+in mOhm to get the actual value.
+
+in0_input     Voltage at Vcc pin in millivolt (range 2.5V to 5V)
+temp1_input   Internal chip temperature in millidegrees Celcius
+curr1_input   Current in mA across v1-v2 assuming a 1mOhm sense resistor.
+curr2_input   Current in mA across v3-v4 assuming a 1mOhm sense resistor.

drivers/hwmon/Kconfig

@@ -685,6 +685,20 @@ config SENSORS_LTC2945
 	  This driver can also be built as a module. If so, the module will
 	  be called ltc2945.
 
+config SENSORS_LTC2990
+	tristate "Linear Technology LTC2990 (current monitoring mode only)"
+	depends on I2C
+	help
+	  If you say yes here you get support for Linear Technology LTC2990
+	  I2C System Monitor. The LTC2990 supports a combination of voltage,
+	  current and temperature monitoring, but in addition to the Vcc supply
+	  voltage and chip temperature, this driver currently only supports
+	  reading two currents by measuring two differential voltages across
+	  series resistors.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc2990.
+
 config SENSORS_LTC4151
 	tristate "Linear Technology LTC4151"
 	depends on I2C

drivers/hwmon/Makefile

@@ -100,6 +100,7 @@ obj-$(CONFIG_SENSORS_LM95234)	+= lm95234.o
 obj-$(CONFIG_SENSORS_LM95241)	+= lm95241.o
 obj-$(CONFIG_SENSORS_LM95245)	+= lm95245.o
 obj-$(CONFIG_SENSORS_LTC2945)	+= ltc2945.o
+obj-$(CONFIG_SENSORS_LTC2990)	+= ltc2990.o
 obj-$(CONFIG_SENSORS_LTC4151)	+= ltc4151.o
 obj-$(CONFIG_SENSORS_LTC4215)	+= ltc4215.o
 obj-$(CONFIG_SENSORS_LTC4222)	+= ltc4222.o

drivers/hwmon/ltc2990.c

@@ -0,0 +1,161 @@
+/*
+ * Driver for Linear Technology LTC2990 power monitor
+ *
+ * Copyright (C) 2014 Topic Embedded Products
+ * Author: Mike Looijmans <mike.looijmans@topic.nl>
+ *
+ * License: GPLv2
+ *
+ * This driver assumes the chip is wired as a dual current monitor, and
+ * reports the voltage drop across two series resistors. It also reports
+ * the chip's internal temperature and Vcc power supply voltage.
+ */
+
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#define LTC2990_STATUS	0x00
+#define LTC2990_CONTROL	0x01
+#define LTC2990_TRIGGER	0x02
+#define LTC2990_TINT_MSB	0x04
+#define LTC2990_V1_MSB	0x06
+#define LTC2990_V2_MSB	0x08
+#define LTC2990_V3_MSB	0x0A
+#define LTC2990_V4_MSB	0x0C
+#define LTC2990_VCC_MSB	0x0E
+
+#define LTC2990_CONTROL_KELVIN		BIT(7)
+#define LTC2990_CONTROL_SINGLE		BIT(6)
+#define LTC2990_CONTROL_MEASURE_ALL	(0x3 << 3)
+#define LTC2990_CONTROL_MODE_CURRENT	0x06
+#define LTC2990_CONTROL_MODE_VOLTAGE	0x07
+
+/* convert raw register value to sign-extended integer in 16-bit range */
+static int ltc2990_voltage_to_int(int raw)
+{
+	if (raw & BIT(14))
+		return -(0x4000 - (raw & 0x3FFF)) << 2;
+	else
+		return (raw & 0x3FFF) << 2;
+}
+
+/* Return the converted value from the given register in uV or mC */
+static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
+{
+	int val;
+
+	val = i2c_smbus_read_word_swapped(i2c, reg);
+	if (unlikely(val < 0))
+		return val;
+
+	switch (reg) {
+	case LTC2990_TINT_MSB:
+		/* internal temp, 0.0625 degrees/LSB, 13-bit  */
+		val = (val & 0x1FFF) << 3;
+		*result = (val * 1000) >> 7;
+		break;
+	case LTC2990_V1_MSB:
+	case LTC2990_V3_MSB:
+		 /* Vx-Vy, 19.42uV/LSB. Depends on mode. */
+		*result = ltc2990_voltage_to_int(val) * 1942 / (4 * 100);
+		break;
+	case LTC2990_VCC_MSB:
+		/* Vcc, 305.18μV/LSB, 2.5V offset */
+		*result = (ltc2990_voltage_to_int(val) * 30518 /
+			   (4 * 100 * 1000)) + 2500;
+		break;
+	default:
+		return -EINVAL; /* won't happen, keep compiler happy */
+	}
+
+	return 0;
+}
+
+static ssize_t ltc2990_show_value(struct device *dev,
+				  struct device_attribute *da, char *buf)
+{
+	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
+	int value;
+	int ret;
+
+	ret = ltc2990_get_value(dev_get_drvdata(dev), attr->index, &value);
+	if (unlikely(ret < 0))
+		return ret;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", value);
+}
+
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, ltc2990_show_value, NULL,
+			  LTC2990_TINT_MSB);
+static SENSOR_DEVICE_ATTR(curr1_input, S_IRUGO, ltc2990_show_value, NULL,
+			  LTC2990_V1_MSB);
+static SENSOR_DEVICE_ATTR(curr2_input, S_IRUGO, ltc2990_show_value, NULL,
+			  LTC2990_V3_MSB);
+static SENSOR_DEVICE_ATTR(in0_input, S_IRUGO, ltc2990_show_value, NULL,
+			  LTC2990_VCC_MSB);
+
+static struct attribute *ltc2990_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	&sensor_dev_attr_curr1_input.dev_attr.attr,
+	&sensor_dev_attr_curr2_input.dev_attr.attr,
+	&sensor_dev_attr_in0_input.dev_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(ltc2990);
+
+static int ltc2990_i2c_probe(struct i2c_client *i2c,
+			     const struct i2c_device_id *id)
+{
+	int ret;
+	struct device *hwmon_dev;
+
+	if (!i2c_check_functionality(i2c->adapter, I2C_FUNC_SMBUS_BYTE_DATA |
+				     I2C_FUNC_SMBUS_WORD_DATA))
+		return -ENODEV;
+
+	/* Setup continuous mode, current monitor */
+	ret = i2c_smbus_write_byte_data(i2c, LTC2990_CONTROL,
+					LTC2990_CONTROL_MEASURE_ALL |
+					LTC2990_CONTROL_MODE_CURRENT);
+	if (ret < 0) {
+		dev_err(&i2c->dev, "Error: Failed to set control mode.\n");
+		return ret;
+	}
+	/* Trigger once to start continuous conversion */
+	ret = i2c_smbus_write_byte_data(i2c, LTC2990_TRIGGER, 1);
+	if (ret < 0) {
+		dev_err(&i2c->dev, "Error: Failed to start acquisition.\n");
+		return ret;
+	}
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(&i2c->dev,
+							   i2c->name,
+							   i2c,
+							   ltc2990_groups);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id ltc2990_i2c_id[] = {
+	{ "ltc2990", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ltc2990_i2c_id);
+
+static struct i2c_driver ltc2990_i2c_driver = {
+	.driver = {
+		.name = "ltc2990",
+	},
+	.probe    = ltc2990_i2c_probe,
+	.id_table = ltc2990_i2c_id,
+};
+
+module_i2c_driver(ltc2990_i2c_driver);
+
+MODULE_DESCRIPTION("LTC2990 Sensor Driver");
+MODULE_AUTHOR("Topic Embedded Products");
+MODULE_LICENSE("GPL v2");