[PATCH] hwmon: Add LTC2471/LTC2473 driver

[Mike Looijmans]

The LTC2741 and LTC2473 are single voltage monitoring chips. The LTC2473
is similar to the LTC2471 but outputs a signed differential value.

Datasheet:
  http://cds.linear.com/docs/en/datasheet/24713fb.pdf

Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>
---
 drivers/hwmon/Kconfig   |  10 ++++
 drivers/hwmon/Makefile  |   1 +
 drivers/hwmon/ltc2471.c | 127 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 138 insertions(+)
 create mode 100644 drivers/hwmon/ltc2471.c

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index fbde226..c9a2a87 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -673,6 +673,16 @@ config SENSORS_LINEAGE
 	  This driver can also be built as a module.  If so, the module
 	  will be called lineage-pem.
 
+config SENSORS_LTC2471
+	tristate "Linear Technology LTC2471 and LTC2473"
+	depends on I2C
+	help
+	  If you say yes here you get support for Linear Technology LTC2471
+	  and LTC2473 voltage monitors.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc2471.
+
 config SENSORS_LTC2945
 	tristate "Linear Technology LTC2945"
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 58cc3ac..6f60fe7 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -99,6 +99,7 @@ obj-$(CONFIG_SENSORS_LM93)	+= lm93.o
 obj-$(CONFIG_SENSORS_LM95234)	+= lm95234.o
 obj-$(CONFIG_SENSORS_LM95241)	+= lm95241.o
 obj-$(CONFIG_SENSORS_LM95245)	+= lm95245.o
+obj-$(CONFIG_SENSORS_LTC2471)	+= ltc2471.o
 obj-$(CONFIG_SENSORS_LTC2945)	+= ltc2945.o
 obj-$(CONFIG_SENSORS_LTC2990)	+= ltc2990.o
 obj-$(CONFIG_SENSORS_LTC4151)	+= ltc4151.o
diff --git a/drivers/hwmon/ltc2471.c b/drivers/hwmon/ltc2471.c
new file mode 100644
index 0000000..17eaad8
--- /dev/null
+++ b/drivers/hwmon/ltc2471.c
@@ -0,0 +1,127 @@
+/*
+ * Driver for Linear Technology LTC2471 and LTC2473 voltage monitors
+ * The LTC2473 is identical to the 2471, but reports a differential signal.
+ *
+ * Copyright (C) 2017 Topic Embedded Products
+ * Author: Mike Looijmans <mike.looijmans@xxxxxxxx>
+ *
+ * License: GPLv2
+ */
+
+#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>
+
+enum chips {
+	ltc2471,
+	ltc2473
+};
+
+struct ltc2471_data {
+	struct i2c_client *i2c;
+	bool differential;
+};
+
+/* Reference voltage is 1.25V */
+#define LTC2471_VREF 1250
+
+/* Read two bytes from the I2C bus to obtain the ADC result */
+static int ltc2471_get_value(struct i2c_client *i2c)
+{
+	int ret;
+	__be16 buf;
+
+	ret = i2c_master_recv(i2c, (char *)&buf, 2);
+	if (ret < 0)
+		return ret;
+	if (ret != 2)
+		return -EIO;
+
+	/* MSB first */
+	return be16_to_cpu(buf);
+}
+
+static ssize_t ltc2471_show_value(struct device *dev,
+				  struct device_attribute *da, char *buf)
+{
+	struct ltc2471_data *data = dev_get_drvdata(dev);
+	int value;
+
+	value = ltc2471_get_value(data->i2c);
+	if (unlikely(value < 0))
+		return value;
+
+	if (data->differential)
+		/* Ranges from -VREF to +VREF with "0" at 0x8000 */
+		value = ((s32)LTC2471_VREF * (s32)(value - 0x8000)) >> 15;
+	else
+		/* Ranges from 0 to +VREF */
+		value = ((u32)LTC2471_VREF * (u32)value) >> 16;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", value);
+}
+
+static SENSOR_DEVICE_ATTR(in0_input, S_IRUGO, ltc2471_show_value, NULL, 0);
+
+static struct attribute *ltc2471_attrs[] = {
+	&sensor_dev_attr_in0_input.dev_attr.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(ltc2471);
+
+static int ltc2471_i2c_probe(struct i2c_client *i2c,
+			     const struct i2c_device_id *id)
+{
+	int ret;
+	struct device *hwmon_dev;
+	struct ltc2471_data *data;
+
+	if (!i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	data = devm_kzalloc(&i2c->dev, sizeof(struct ltc2471_data), GFP_KERNEL);
+	if (unlikely(!data))
+		return -ENOMEM;
+
+	data->i2c = i2c;
+	data->differential = (id->driver_data == ltc2473);
+
+	/* Trigger once to start conversion and check if chip is there */
+	ret = ltc2471_get_value(i2c);
+	if (ret < 0) {
+		dev_err(&i2c->dev, "Cannot read from device.\n");
+		return ret;
+	}
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(&i2c->dev,
+							   i2c->name,
+							   data,
+							   ltc2471_groups);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id ltc2471_i2c_id[] = {
+	{ "ltc2471", ltc2471 },
+	{ "ltc2473", ltc2473 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ltc2471_i2c_id);
+
+static struct i2c_driver ltc2471_i2c_driver = {
+	.driver = {
+		.name = "ltc2471",
+	},
+	.probe    = ltc2471_i2c_probe,
+	.id_table = ltc2471_i2c_id,
+};
+
+module_i2c_driver(ltc2471_i2c_driver);
+
+MODULE_DESCRIPTION("LTC2471/LTC2473 Sensor Driver");
+MODULE_AUTHOR("Topic Embedded Products");
+MODULE_LICENSE("GPL v2");
-- 
1.9.1