hwmon: Add LTC4215 driver

Add Linux support for the Linear Technology LTC4215 Hot Swap controller
I2C monitoring interface.

I have tested the driver with my board, and it appears to work fine.  With
the power supplies disabled, it reads 11.93V input, 1.93V output, no
current and no power.  With the supplies enabled, it reads 11.93V input,
11.98V output, no current, no power.  I'm not drawing any current at the
moment, so this is reasonable.  The value in the sense register never
reads anything except 0, so I expect to get zero from the current and
power calculations.

I didn't attempt to support changing any of the chip's settings or
enabling the FET.  I'm not sure even how to do that and still fit within
the hwmon framework.  :)
Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: "Mark M. Hoffman" <mhoffman@lightlink.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/hwmon/ltc4215

+Kernel driver ltc4215
+=====================
+
+Supported chips:
+  * Linear Technology LTC4215
+    Prefix: 'ltc4215'
+    Addresses scanned: 0x44
+    Datasheet:
+        http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1006,C1163,P17572,D12697
+
+Author: Ira W. Snyder <iws@ovro.caltech.edu>
+
+
+Description
+-----------
+
+The LTC4215 controller allows a board to be safely inserted and removed
+from a live backplane.
+
+
+Usage Notes
+-----------
+
+This driver does not probe for LTC4215 devices, due to the fact that some
+of the possible addresses are unfriendly to probing. You will need to use
+the "force" parameter to tell the driver where to find the device.
+
+Example: the following will load the driver for an LTC4215 at address 0x44
+on I2C bus #0:
+$ modprobe ltc4215 force=0,0x44
+
+
+Sysfs entries
+-------------
+
+The LTC4215 has built-in limits for overvoltage, undervoltage, and
+undercurrent warnings. This makes it very likely that the reference
+circuit will be used.
+
+in1_input		input voltage
+in2_input		output voltage
+
+in1_min_alarm		input undervoltage alarm
+in1_max_alarm		input overvoltage alarm
+
+curr1_input		current
+curr1_max_alarm		overcurrent alarm
+
+power1_input		power usage
+power1_alarm		power bad alarm

drivers/hwmon/Kconfig

@@ -571,6 +571,17 @@ config SENSORS_LM93
 	  This driver can also be built as a module.  If so, the module
 	  will be called lm93.
 
+config SENSORS_LTC4215
+	tristate "Linear Technology LTC4215"
+	depends on I2C && EXPERIMENTAL
+	default n
+	help
+	  If you say yes here you get support for Linear Technology LTC4215
+	  Hot Swap Controller I2C interface.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc4215.
+
 config SENSORS_LTC4245
 	tristate "Linear Technology LTC4245"
 	depends on I2C && EXPERIMENTAL

drivers/hwmon/Makefile

@@ -65,6 +65,7 @@ obj-$(CONFIG_SENSORS_LM90)	+= lm90.o
 obj-$(CONFIG_SENSORS_LM92)	+= lm92.o
 obj-$(CONFIG_SENSORS_LM93)	+= lm93.o
 obj-$(CONFIG_SENSORS_LM95241)	+= lm95241.o
+obj-$(CONFIG_SENSORS_LTC4215)	+= ltc4215.o
 obj-$(CONFIG_SENSORS_LTC4245)	+= ltc4245.o
 obj-$(CONFIG_SENSORS_MAX1111)	+= max1111.o
 obj-$(CONFIG_SENSORS_MAX1619)	+= max1619.o

drivers/hwmon/ltc4215.c

+/*
+ * Driver for Linear Technology LTC4215 I2C Hot Swap Controller
+ *
+ * Copyright (C) 2009 Ira W. Snyder <iws@ovro.caltech.edu>
+ *
+ * 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; version 2 of the License.
+ *
+ * Datasheet:
+ * http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1006,C1163,P17572,D12697
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+
+static const unsigned short normal_i2c[] = { I2C_CLIENT_END };
+
+/* Insmod parameters */
+I2C_CLIENT_INSMOD_1(ltc4215);
+
+/* Here are names of the chip's registers (a.k.a. commands) */
+enum ltc4215_cmd {
+	LTC4215_CONTROL			= 0x00, /* rw */
+	LTC4215_ALERT			= 0x01, /* rw */
+	LTC4215_STATUS			= 0x02, /* ro */
+	LTC4215_FAULT			= 0x03, /* rw */
+	LTC4215_SENSE			= 0x04, /* rw */
+	LTC4215_SOURCE			= 0x05, /* rw */
+	LTC4215_ADIN			= 0x06, /* rw */
+};
+
+struct ltc4215_data {
+	struct device *hwmon_dev;
+
+	struct mutex update_lock;
+	bool valid;
+	unsigned long last_updated; /* in jiffies */
+
+	/* Registers */
+	u8 regs[7];
+};
+
+static struct ltc4215_data *ltc4215_update_device(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct ltc4215_data *data = i2c_get_clientdata(client);
+	s32 val;
+	int i;
+
+	mutex_lock(&data->update_lock);
+
+	/* The chip's A/D updates 10 times per second */
+	if (time_after(jiffies, data->last_updated + HZ / 10) || !data->valid) {
+
+		dev_dbg(&client->dev, "Starting ltc4215 update\n");
+
+		/* Read all registers */
+		for (i = 0; i < ARRAY_SIZE(data->regs); i++) {
+			val = i2c_smbus_read_byte_data(client, i);
+			if (unlikely(val < 0))
+				data->regs[i] = 0;
+			else
+				data->regs[i] = val;
+		}
+
+		data->last_updated = jiffies;
+		data->valid = 1;
+	}
+
+	mutex_unlock(&data->update_lock);
+
+	return data;
+}
+
+/* Return the voltage from the given register in millivolts */
+static int ltc4215_get_voltage(struct device *dev, u8 reg)
+{
+	struct ltc4215_data *data = ltc4215_update_device(dev);
+	const u8 regval = data->regs[reg];
+	u32 voltage = 0;
+
+	switch (reg) {
+	case LTC4215_SENSE:
+		/* 151 uV per increment */
+		voltage = regval * 151 / 1000;
+		break;
+	case LTC4215_SOURCE:
+		/* 60.5 mV per increment */
+		voltage = regval * 605 / 10;
+		break;
+	case LTC4215_ADIN:
+		/* The ADIN input is divided by 12.5, and has 4.82 mV
+		 * per increment, so we have the additional multiply */
+		voltage = regval * 482 * 125 / 1000;
+		break;
+	default:
+		/* If we get here, the developer messed up */
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	return voltage;
+}
+
+/* Return the current from the sense resistor in mA */
+static unsigned int ltc4215_get_current(struct device *dev)
+{
+	struct ltc4215_data *data = ltc4215_update_device(dev);
+
+	/* The strange looking conversions that follow are fixed-point
+	 * math, since we cannot do floating point in the kernel.
+	 *
+	 * Step 1: convert sense register to microVolts
+	 * Step 2: convert voltage to milliAmperes
+	 *
+	 * If you play around with the V=IR equation, you come up with
+	 * the following: X uV / Y mOhm == Z mA
+	 *
+	 * With the resistors that are fractions of a milliOhm, we multiply
+	 * the voltage and resistance by 10, to shift the decimal point.
+	 * Now we can use the normal division operator again.
+	 */
+
+	/* Calculate voltage in microVolts (151 uV per increment) */
+	const unsigned int voltage = data->regs[LTC4215_SENSE] * 151;
+
+	/* Calculate current in milliAmperes (4 milliOhm sense resistor) */
+	const unsigned int curr = voltage / 4;
+
+	return curr;
+}
+
+static ssize_t ltc4215_show_voltage(struct device *dev,
+				    struct device_attribute *da,
+				    char *buf)
+{
+	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
+	const int voltage = ltc4215_get_voltage(dev, attr->index);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", voltage);
+}
+
+static ssize_t ltc4215_show_current(struct device *dev,
+				    struct device_attribute *da,
+				    char *buf)
+{
+	const unsigned int curr = ltc4215_get_current(dev);
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", curr);
+}
+
+static ssize_t ltc4215_show_power(struct device *dev,
+				  struct device_attribute *da,
+				  char *buf)
+{
+	const unsigned int curr = ltc4215_get_current(dev);
+	const int output_voltage = ltc4215_get_voltage(dev, LTC4215_ADIN);
+
+	/* current in mA * voltage in mV == power in uW */
+	const unsigned int power = abs(output_voltage * curr);
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", power);
+}
+
+static ssize_t ltc4215_show_alarm(struct device *dev,
+					  struct device_attribute *da,
+					  char *buf)
+{
+	struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(da);
+	struct ltc4215_data *data = ltc4215_update_device(dev);
+	const u8 reg = data->regs[attr->index];
+	const u32 mask = attr->nr;
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", (reg & mask) ? 1 : 0);
+}
+
+/* These macros are used below in constructing device attribute objects
+ * for use with sysfs_create_group() to make a sysfs device file
+ * for each register.
+ */
+
+#define LTC4215_VOLTAGE(name, ltc4215_cmd_idx) \
+	static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
+	ltc4215_show_voltage, NULL, ltc4215_cmd_idx)
+
+#define LTC4215_CURRENT(name) \
+	static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
+	ltc4215_show_current, NULL, 0);
+
+#define LTC4215_POWER(name) \
+	static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
+	ltc4215_show_power, NULL, 0);
+
+#define LTC4215_ALARM(name, mask, reg) \
+	static SENSOR_DEVICE_ATTR_2(name, S_IRUGO, \
+	ltc4215_show_alarm, NULL, (mask), reg)
+
+/* Construct a sensor_device_attribute structure for each register */
+
+/* Current */
+LTC4215_CURRENT(curr1_input);
+LTC4215_ALARM(curr1_max_alarm,	(1 << 2),	LTC4215_STATUS);
+
+/* Power (virtual) */
+LTC4215_POWER(power1_input);
+LTC4215_ALARM(power1_alarm,	(1 << 3),	LTC4215_STATUS);
+
+/* Input Voltage */
+LTC4215_VOLTAGE(in1_input,			LTC4215_ADIN);
+LTC4215_ALARM(in1_max_alarm,	(1 << 0),	LTC4215_STATUS);
+LTC4215_ALARM(in1_min_alarm,	(1 << 1),	LTC4215_STATUS);
+
+/* Output Voltage */
+LTC4215_VOLTAGE(in2_input,			LTC4215_SOURCE);
+
+/* Finally, construct an array of pointers to members of the above objects,
+ * as required for sysfs_create_group()
+ */
+static struct attribute *ltc4215_attributes[] = {
+	&sensor_dev_attr_curr1_input.dev_attr.attr,
+	&sensor_dev_attr_curr1_max_alarm.dev_attr.attr,
+
+	&sensor_dev_attr_power1_input.dev_attr.attr,
+	&sensor_dev_attr_power1_alarm.dev_attr.attr,
+
+	&sensor_dev_attr_in1_input.dev_attr.attr,
+	&sensor_dev_attr_in1_max_alarm.dev_attr.attr,
+	&sensor_dev_attr_in1_min_alarm.dev_attr.attr,
+
+	&sensor_dev_attr_in2_input.dev_attr.attr,
+
+	NULL,
+};
+
+static const struct attribute_group ltc4215_group = {
+	.attrs = ltc4215_attributes,
+};
+
+static int ltc4215_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct ltc4215_data *data;
+	int ret;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data) {
+		ret = -ENOMEM;
+		goto out_kzalloc;
+	}
+
+	i2c_set_clientdata(client, data);
+	mutex_init(&data->update_lock);
+
+	/* Initialize the LTC4215 chip */
+	/* TODO */
+
+	/* Register sysfs hooks */
+	ret = sysfs_create_group(&client->dev.kobj, &ltc4215_group);
+	if (ret)
+		goto out_sysfs_create_group;
+
+	data->hwmon_dev = hwmon_device_register(&client->dev);
+	if (IS_ERR(data->hwmon_dev)) {
+		ret = PTR_ERR(data->hwmon_dev);
+		goto out_hwmon_device_register;
+	}
+
+	return 0;
+
+out_hwmon_device_register:
+	sysfs_remove_group(&client->dev.kobj, &ltc4215_group);
+out_sysfs_create_group:
+	kfree(data);
+out_kzalloc:
+	return ret;
+}
+
+static int ltc4215_remove(struct i2c_client *client)
+{
+	struct ltc4215_data *data = i2c_get_clientdata(client);
+
+	hwmon_device_unregister(data->hwmon_dev);
+	sysfs_remove_group(&client->dev.kobj, &ltc4215_group);
+
+	kfree(data);
+
+	return 0;
+}
+
+static int ltc4215_detect(struct i2c_client *client,
+			  int kind,
+			  struct i2c_board_info *info)
+{
+	struct i2c_adapter *adapter = client->adapter;
+
+	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+		return -ENODEV;
+
+	if (kind < 0) {		/* probed detection - check the chip type */
+		s32 v;		/* 8 bits from the chip, or -ERRNO */
+
+		/*
+		 * Register 0x01 bit b7 is reserved, expect 0
+		 * Register 0x03 bit b6 and b7 are reserved, expect 0
+		 */
+		v = i2c_smbus_read_byte_data(client, LTC4215_ALERT);
+		if (v < 0 || (v & (1 << 7)) != 0)
+			return -ENODEV;
+
+		v = i2c_smbus_read_byte_data(client, LTC4215_FAULT);
+		if (v < 0 || (v & ((1 << 6) | (1 << 7))) != 0)
+				return -ENODEV;
+	}
+
+	strlcpy(info->type, "ltc4215", I2C_NAME_SIZE);
+	dev_info(&adapter->dev, "ltc4215 %s at address 0x%02x\n",
+			kind < 0 ? "probed" : "forced",
+			client->addr);
+
+	return 0;
+}
+
+static const struct i2c_device_id ltc4215_id[] = {
+	{ "ltc4215", ltc4215 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc4215_id);
+
+/* This is the driver that will be inserted */
+static struct i2c_driver ltc4215_driver = {
+	.class		= I2C_CLASS_HWMON,
+	.driver = {
+		.name	= "ltc4215",
+	},
+	.probe		= ltc4215_probe,
+	.remove		= ltc4215_remove,
+	.id_table	= ltc4215_id,
+	.detect		= ltc4215_detect,
+	.address_data	= &addr_data,
+};
+
+static int __init ltc4215_init(void)
+{
+	return i2c_add_driver(&ltc4215_driver);
+}
+
+static void __exit ltc4215_exit(void)
+{
+	i2c_del_driver(&ltc4215_driver);
+}
+
+MODULE_AUTHOR("Ira W. Snyder <iws@ovro.caltech.edu>");
+MODULE_DESCRIPTION("LTC4215 driver");
+MODULE_LICENSE("GPL");
+
+module_init(ltc4215_init);
+module_exit(ltc4215_exit);