diff --git a/Documentation/hwmon/ltc4215 b/Documentation/hwmon/ltc4215
new file mode 100644
index 0000000000000000000000000000000000000000..2e6a21eb656c556ce4e4c154a6e1229c35275938
--- /dev/null
+++ b/Documentation/hwmon/ltc4215
@@ -0,0 +1,50 @@
+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
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 8a91c9971558d9925a363a5693f204854ca100f7..bc6810c22dd76c4ea9a2ff25504bfba0e6500422 100644
--- a/drivers/hwmon/Kconfig
+++ b/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
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 81c88822a3ebfd39502de72211252e69345cb30a..4da261d16abfb66ea21114251b2ac567e456f8c4 100644
--- a/drivers/hwmon/Makefile
+++ b/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
diff --git a/drivers/hwmon/ltc4215.c b/drivers/hwmon/ltc4215.c
new file mode 100644
index 0000000000000000000000000000000000000000..9386e2a39211f75e9a610e899fc43ff755c9dc25
--- /dev/null
+++ b/drivers/hwmon/ltc4215.c
@@ -0,0 +1,364 @@
+/*
+ * 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, <c4215_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, <c4215_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, <c4215_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(<c4215_driver);
+}
+
+static void __exit ltc4215_exit(void)
+{
+ i2c_del_driver(<c4215_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);