hwmon: New max6650 driver

This driver supports the Maxim MAX6650 and MAX6651 fan speed
monitoring and control chips.

Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

5 files changed, 763 insertions, 0 deletions

diff --git a/Documentation/hwmon/max6650 b/Documentation/hwmon/max6650
new file mode 100644
index 000000000000..8be7beb9e3e8
--- /dev/null
+++ b/Documentation/hwmon/max6650
@@ -0,0 +1,53 @@
+Kernel driver max6650
+=====================
+
+Supported chips:
+  * Maxim 6650 / 6651
+    Prefix: 'max6650'
+    Addresses scanned: I2C 0x1b, 0x1f, 0x48, 0x4b
+    Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6650-MAX6651.pdf
+
+Authors:
+    Hans J. Koch <hjk@linutronix.de>
+    John Morris <john.morris@spirentcom.com>
+    Claus Gindhart <claus.gindhart@kontron.com>
+
+Description
+-----------
+
+This driver implements support for the Maxim 6650/6651
+
+The 2 devices are very similar, but the Maxim 6550 has a reduced feature
+set, e.g. only one fan-input, instead of 4 for the 6651.
+
+The driver is not able to distinguish between the 2 devices.
+
+The driver provides the following sensor accesses in sysfs:
+
+fan1_input      ro      fan tachometer speed in RPM
+fan2_input      ro      "
+fan3_input      ro      "
+fan4_input      ro      "
+fan1_target     rw      desired fan speed in RPM (closed loop mode only)
+pwm1_enable     rw      regulator mode, 0=full on, 1=open loop, 2=closed loop
+pwm1            rw      relative speed (0-255), 255=max. speed.
+                        Used in open loop mode only.
+fan1_div        rw      sets the speed range the inputs can handle. Legal
+                        values are 1, 2, 4, and 8. Use lower values for
+                        faster fans.
+
+Module parameters
+-----------------
+
+If your board has a BIOS that initializes the MAX6650/6651 correctly, you can
+simply load your module without parameters. It won't touch the configuration
+registers then. If your board BIOS doesn't initialize the chip, or you want
+different settings, you can set the following parameters:
+
+voltage_12V: 5=5V fan, 12=12V fan, 0=don't change
+prescaler: Possible values are 1,2,4,8,16, or 0 for don't change
+clock: The clock frequency in Hz of the chip the driver should assume [254000]
+
+Please have a look at the MAX6650/6651 data sheet and make sure that you fully
+understand the meaning of these parameters before you attempt to change them.
+
diff --git a/MAINTAINERS b/MAINTAINERS
index 6d665ac13f99..a328862731c6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2304,6 +2304,12 @@ M:	vandrove@vc.cvut.cz
 L:      linux-fbdev-devel@lists.sourceforge.net (subscribers-only)
 S:      Maintained
 
+MAX6650 HARDWARE MONITOR AND FAN CONTROLLER DRIVER
+P:      Hans J. Koch
+M:      hjk@linutronix.de
+L:      lm-sensors@lm-sensors.org
+S:      Maintained
+
 MEGARAID SCSI DRIVERS
 P:      Neela Syam Kolli
 M:      Neela.Kolli@engenio.com
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 6362d02b18df..d89bd5eb50ae 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -375,6 +375,16 @@ config SENSORS_MAX1619
           This driver can also be built as a module.  If so, the module
           will be called max1619.
 
+config SENSORS_MAX6650
+        tristate "Maxim MAX6650 sensor chip"
+        depends on HWMON && I2C && EXPERIMENTAL
+        help
+          If you say yes here you get support for the MAX6650 / MAX6651
+          sensor chips.
+
+          This driver can also be built as a module.  If so, the module
+          will be called max6650.
+
 config SENSORS_PC87360
         tristate "National Semiconductor PC87360 family"
         depends on HWMON && I2C && EXPERIMENTAL
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 4165c27a2f25..bbbe86bf5da1 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_SENSORS_LM87)	+= lm87.o
 obj-$(CONFIG_SENSORS_LM90)      += lm90.o
 obj-$(CONFIG_SENSORS_LM92)      += lm92.o
 obj-$(CONFIG_SENSORS_MAX1619)   += max1619.o
+obj-$(CONFIG_SENSORS_MAX6650)   += max6650.o
 obj-$(CONFIG_SENSORS_PC87360)   += pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)   += pc87427.o
 obj-$(CONFIG_SENSORS_SIS5595)   += sis5595.o
diff --git a/drivers/hwmon/max6650.c b/drivers/hwmon/max6650.c
new file mode 100644
index 000000000000..8415664f33c2
--- /dev/null
+++ b/drivers/hwmon/max6650.c
@@ -0,0 +1,693 @@
+/*
+ * max6650.c - Part of lm_sensors, Linux kernel modules for hardware
+ *             monitoring.
+ *
+ * (C) 2007 by Hans J. Koch <hjk@linutronix.de>
+ *
+ * based on code written by John Morris <john.morris@spirentcom.com>
+ * Copyright (c) 2003 Spirent Communications
+ * and Claus Gindhart <claus.gindhart@kontron.com>
+ *
+ * This module has only been tested with the MAX6650 chip. It should
+ * also work with the MAX6651. It does not distinguish max6650 and max6651
+ * chips.
+ *
+ * Tha datasheet was last seen at:
+ *
+ *        http://pdfserv.maxim-ic.com/en/ds/MAX6650-MAX6651.pdf
+ *
+ * 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/jiffies.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/err.h>
+
+/*
+ * Addresses to scan. There are four disjoint possibilities, by pin config.
+ */
+
+static unsigned short normal_i2c[] = {0x1b, 0x1f, 0x48, 0x4b, I2C_CLIENT_END};
+
+/*
+ * Insmod parameters
+ */
+
+/* fan_voltage: 5=5V fan, 12=12V fan, 0=don't change */
+static int fan_voltage;
+/* prescaler: Possible values are 1, 2, 4, 8, 16 or 0 for don't change */
+static int prescaler;
+/* clock: The clock frequency of the chip the driver should assume */
+static int clock = 254000;
+
+module_param(fan_voltage, int, S_IRUGO);
+module_param(prescaler, int, S_IRUGO);
+module_param(clock, int, S_IRUGO);
+
+I2C_CLIENT_INSMOD_1(max6650);
+
+/*
+ * MAX 6650/6651 registers
+ */
+
+#define MAX6650_REG_SPEED       0x00
+#define MAX6650_REG_CONFIG      0x02
+#define MAX6650_REG_GPIO_DEF    0x04
+#define MAX6650_REG_DAC         0x06
+#define MAX6650_REG_ALARM_EN    0x08
+#define MAX6650_REG_ALARM       0x0A
+#define MAX6650_REG_TACH0       0x0C
+#define MAX6650_REG_TACH1       0x0E
+#define MAX6650_REG_TACH2       0x10
+#define MAX6650_REG_TACH3       0x12
+#define MAX6650_REG_GPIO_STAT   0x14
+#define MAX6650_REG_COUNT       0x16
+
+/*
+ * Config register bits
+ */
+
+#define MAX6650_CFG_V12                 0x08
+#define MAX6650_CFG_PRESCALER_MASK      0x07
+#define MAX6650_CFG_PRESCALER_2         0x01
+#define MAX6650_CFG_PRESCALER_4         0x02
+#define MAX6650_CFG_PRESCALER_8         0x03
+#define MAX6650_CFG_PRESCALER_16        0x04
+#define MAX6650_CFG_MODE_MASK           0x30
+#define MAX6650_CFG_MODE_ON             0x00
+#define MAX6650_CFG_MODE_OFF            0x10
+#define MAX6650_CFG_MODE_CLOSED_LOOP    0x20
+#define MAX6650_CFG_MODE_OPEN_LOOP      0x30
+#define MAX6650_COUNT_MASK              0x03
+
+/* Minimum and maximum values of the FAN-RPM */
+#define FAN_RPM_MIN 240
+#define FAN_RPM_MAX 30000
+
+#define DIV_FROM_REG(reg) (1 << (reg & 7))
+
+static int max6650_attach_adapter(struct i2c_adapter *adapter);
+static int max6650_detect(struct i2c_adapter *adapter, int address, int kind);
+static int max6650_init_client(struct i2c_client *client);
+static int max6650_detach_client(struct i2c_client *client);
+static struct max6650_data *max6650_update_device(struct device *dev);
+
+/*
+ * Driver data (common to all clients)
+ */
+
+static struct i2c_driver max6650_driver = {
+        .driver = {
+                .name   = "max6650",
+        },
+        .attach_adapter = max6650_attach_adapter,
+        .detach_client  = max6650_detach_client,
+};
+
+/*
+ * Client data (each client gets its own)
+ */
+
+struct max6650_data
+{
+        struct i2c_client client;
+        struct class_device *class_dev;
+        struct mutex update_lock;
+        char valid; /* zero until following fields are valid */
+        unsigned long last_updated; /* in jiffies */
+
+        /* register values */
+        u8 speed;
+        u8 config;
+        u8 tach[4];
+        u8 count;
+        u8 dac;
+};
+
+static ssize_t get_fan(struct device *dev, struct device_attribute *devattr,
+                       char *buf)
+{
+        struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
+        struct max6650_data *data = max6650_update_device(dev);
+        int rpm;
+
+        /*
+        * Calculation details:
+        *
+        * Each tachometer counts over an interval given by the "count"
+        * register (0.25, 0.5, 1 or 2 seconds). This module assumes
+        * that the fans produce two pulses per revolution (this seems
+        * to be the most common).
+        */
+
+        rpm = ((data->tach[attr->index] * 120) / DIV_FROM_REG(data->count));
+        return sprintf(buf, "%d\n", rpm);
+}
+
+/*
+ * Set the fan speed to the specified RPM (or read back the RPM setting).
+ * This works in closed loop mode only. Use pwm1 for open loop speed setting.
+ *
+ * The MAX6650/1 will automatically control fan speed when in closed loop
+ * mode.
+ *
+ * Assumptions:
+ *
+ * 1) The MAX6650/1 internal 254kHz clock frequency is set correctly. Use
+ *    the clock module parameter if you need to fine tune this.
+ *
+ * 2) The prescaler (low three bits of the config register) has already
+ *    been set to an appropriate value. Use the prescaler module parameter
+ *    if your BIOS doesn't initialize the chip properly.
+ *
+ * The relevant equations are given on pages 21 and 22 of the datasheet.
+ *
+ * From the datasheet, the relevant equation when in regulation is:
+ *
+ *    [fCLK / (128 x (KTACH + 1))] = 2 x FanSpeed / KSCALE
+ *
+ * where:
+ *
+ *    fCLK is the oscillator frequency (either the 254kHz internal
+ *         oscillator or the externally applied clock)
+ *
+ *    KTACH is the value in the speed register
+ *
+ *    FanSpeed is the speed of the fan in rps
+ *
+ *    KSCALE is the prescaler value (1, 2, 4, 8, or 16)
+ *
+ * When reading, we need to solve for FanSpeed. When writing, we need to
+ * solve for KTACH.
+ *
+ * Note: this tachometer is completely separate from the tachometers
+ * used to measure the fan speeds. Only one fan's speed (fan1) is
+ * controlled.
+ */
+
+static ssize_t get_target(struct device *dev, struct device_attribute *devattr,
+                         char *buf)
+{
+        struct max6650_data *data = max6650_update_device(dev);
+        int kscale, ktach, rpm;
+
+        /*
+        * Use the datasheet equation:
+        *
+        *    FanSpeed = KSCALE x fCLK / [256 x (KTACH + 1)]
+        *
+        * then multiply by 60 to give rpm.
+        */
+
+        kscale = DIV_FROM_REG(data->config);
+        ktach = data->speed;
+        rpm = 60 * kscale * clock / (256 * (ktach + 1));
+        return sprintf(buf, "%d\n", rpm);
+}
+
+static ssize_t set_target(struct device *dev, struct device_attribute *devattr,
+                         const char *buf, size_t count)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int rpm = simple_strtoul(buf, NULL, 10);
+        int kscale, ktach;
+
+        rpm = SENSORS_LIMIT(rpm, FAN_RPM_MIN, FAN_RPM_MAX);
+
+        /*
+        * Divide the required speed by 60 to get from rpm to rps, then
+        * use the datasheet equation:
+        *
+        *     KTACH = [(fCLK x KSCALE) / (256 x FanSpeed)] - 1
+        */
+
+        mutex_lock(&data->update_lock);
+
+        kscale = DIV_FROM_REG(data->config);
+        ktach = ((clock * kscale) / (256 * rpm / 60)) - 1;
+        if (ktach < 0)
+                ktach = 0;
+        if (ktach > 255)
+                ktach = 255;
+        data->speed = ktach;
+
+        i2c_smbus_write_byte_data(client, MAX6650_REG_SPEED, data->speed);
+
+        mutex_unlock(&data->update_lock);
+
+        return count;
+}
+
+/*
+ * Get/set the fan speed in open loop mode using pwm1 sysfs file.
+ * Speed is given as a relative value from 0 to 255, where 255 is maximum
+ * speed. Note that this is done by writing directly to the chip's DAC,
+ * it won't change the closed loop speed set by fan1_target.
+ * Also note that due to rounding errors it is possible that you don't read
+ * back exactly the value you have set.
+ */
+
+static ssize_t get_pwm(struct device *dev, struct device_attribute *devattr,
+                       char *buf)
+{
+        int pwm;
+        struct max6650_data *data = max6650_update_device(dev);
+
+        /* Useful range for dac is 0-180 for 12V fans and 0-76 for 5V fans.
+           Lower DAC values mean higher speeds. */
+        if (data->config & MAX6650_CFG_V12)
+                pwm = 255 - (255 * (int)data->dac)/180;
+        else
+                pwm = 255 - (255 * (int)data->dac)/76;
+
+        if (pwm < 0)
+                pwm = 0;
+
+        return sprintf(buf, "%d\n", pwm);
+}
+
+static ssize_t set_pwm(struct device *dev, struct device_attribute *devattr,
+                        const char *buf, size_t count)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int pwm = simple_strtoul(buf, NULL, 10);
+
+        pwm = SENSORS_LIMIT(pwm, 0, 255);
+
+        mutex_lock(&data->update_lock);
+
+        if (data->config & MAX6650_CFG_V12)
+                data->dac = 180 - (180 * pwm)/255;
+        else
+                data->dac = 76 - (76 * pwm)/255;
+
+        i2c_smbus_write_byte_data(client, MAX6650_REG_DAC, data->dac);
+
+        mutex_unlock(&data->update_lock);
+
+        return count;
+}
+
+/*
+ * Get/Set controller mode:
+ * Possible values:
+ * 0 = Fan always on
+ * 1 = Open loop, Voltage is set according to speed, not regulated.
+ * 2 = Closed loop, RPM for all fans regulated by fan1 tachometer
+ */
+
+static ssize_t get_enable(struct device *dev, struct device_attribute *devattr,
+                          char *buf)
+{
+        struct max6650_data *data = max6650_update_device(dev);
+        int mode = (data->config & MAX6650_CFG_MODE_MASK) >> 4;
+        int sysfs_modes[4] = {0, 1, 2, 1};
+
+        return sprintf(buf, "%d\n", sysfs_modes[mode]);
+}
+
+static ssize_t set_enable(struct device *dev, struct device_attribute *devattr,
+                          const char *buf, size_t count)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int mode = simple_strtoul(buf, NULL, 10);
+        int max6650_modes[3] = {0, 3, 2};
+
+        if ((mode < 0)||(mode > 2)) {
+                dev_err(&client->dev,
+                        "illegal value for pwm1_enable (%d)\n", mode);
+                return -EINVAL;
+        }
+
+        mutex_lock(&data->update_lock);
+
+        data->config = i2c_smbus_read_byte_data(client, MAX6650_REG_CONFIG);
+        data->config = (data->config & ~MAX6650_CFG_MODE_MASK)
+                       | (max6650_modes[mode] << 4);
+
+        i2c_smbus_write_byte_data(client, MAX6650_REG_CONFIG, data->config);
+
+        mutex_unlock(&data->update_lock);
+
+        return count;
+}
+
+/*
+ * Read/write functions for fan1_div sysfs file. The MAX6650 has no such
+ * divider. We handle this by converting between divider and counttime:
+ *
+ * (counttime == k) <==> (divider == 2^k), k = 0, 1, 2, or 3
+ *
+ * Lower values of k allow to connect a faster fan without the risk of
+ * counter overflow. The price is lower resolution. You can also set counttime
+ * using the module parameter. Note that the module parameter "prescaler" also
+ * influences the behaviour. Unfortunately, there's no sysfs attribute
+ * defined for that. See the data sheet for details.
+ */
+
+static ssize_t get_div(struct device *dev, struct device_attribute *devattr,
+                       char *buf)
+{
+        struct max6650_data *data = max6650_update_device(dev);
+
+        return sprintf(buf, "%d\n", DIV_FROM_REG(data->count));
+}
+
+static ssize_t set_div(struct device *dev, struct device_attribute *devattr,
+                       const char *buf, size_t count)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int div = simple_strtoul(buf, NULL, 10);
+
+        mutex_lock(&data->update_lock);
+        switch (div) {
+        case 1:
+                data->count = 0;
+                break;
+        case 2:
+                data->count = 1;
+                break;
+        case 4:
+                data->count = 2;
+                break;
+        case 8:
+                data->count = 3;
+                break;
+        default:
+                dev_err(&client->dev,
+                        "illegal value for fan divider (%d)\n", div);
+                return -EINVAL;
+        }
+
+        i2c_smbus_write_byte_data(client, MAX6650_REG_COUNT, data->count);
+        mutex_unlock(&data->update_lock);
+
+        return count;
+}
+
+static SENSOR_DEVICE_ATTR(fan1_input, S_IRUGO, get_fan, NULL, 0);
+static SENSOR_DEVICE_ATTR(fan2_input, S_IRUGO, get_fan, NULL, 1);
+static SENSOR_DEVICE_ATTR(fan3_input, S_IRUGO, get_fan, NULL, 2);
+static SENSOR_DEVICE_ATTR(fan4_input, S_IRUGO, get_fan, NULL, 3);
+static DEVICE_ATTR(fan1_target, S_IWUSR | S_IRUGO, get_target, set_target);
+static DEVICE_ATTR(fan1_div, S_IWUSR | S_IRUGO, get_div, set_div);
+static DEVICE_ATTR(pwm1_enable, S_IWUSR | S_IRUGO, get_enable, set_enable);
+static DEVICE_ATTR(pwm1, S_IWUSR | S_IRUGO, get_pwm, set_pwm);
+
+
+static struct attribute *max6650_attrs[] = {
+        &sensor_dev_attr_fan1_input.dev_attr.attr,
+        &sensor_dev_attr_fan2_input.dev_attr.attr,
+        &sensor_dev_attr_fan3_input.dev_attr.attr,
+        &sensor_dev_attr_fan4_input.dev_attr.attr,
+        &dev_attr_fan1_target.attr,
+        &dev_attr_fan1_div.attr,
+        &dev_attr_pwm1_enable.attr,
+        &dev_attr_pwm1.attr,
+        NULL
+};
+
+static struct attribute_group max6650_attr_grp = {
+        .attrs = max6650_attrs,
+};
+
+/*
+ * Real code
+ */
+
+static int max6650_attach_adapter(struct i2c_adapter *adapter)
+{
+        if (!(adapter->class & I2C_CLASS_HWMON)) {
+                dev_dbg(&adapter->dev,
+                        "FATAL: max6650_attach_adapter class HWMON not set\n");
+                return 0;
+        }
+
+        return i2c_probe(adapter, &addr_data, max6650_detect);
+}
+
+/*
+ * The following function does more than just detection. If detection
+ * succeeds, it also registers the new chip.
+ */
+
+static int max6650_detect(struct i2c_adapter *adapter, int address, int kind)
+{
+        struct i2c_client *client;
+        struct max6650_data *data;
+        int err = -ENODEV;
+
+        dev_dbg(&adapter->dev, "max6650_detect called, kind = %d\n", kind);
+
+        if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA)) {
+                dev_dbg(&adapter->dev, "max6650: I2C bus doesn't support "
+                                        "byte read mode, skipping.\n");
+                return 0;
+        }
+
+        if (!(data = kzalloc(sizeof(struct max6650_data), GFP_KERNEL))) {
+                dev_err(&adapter->dev, "max6650: out of memory.\n");
+                return -ENOMEM;
+        }
+
+        client = &data->client;
+        i2c_set_clientdata(client, data);
+        client->addr = address;
+        client->adapter = adapter;
+        client->driver = &max6650_driver;
+
+        /*
+         * Now we do the remaining detection. A negative kind means that
+         * the driver was loaded with no force parameter (default), so we
+         * must both detect and identify the chip (actually there is only
+         * one possible kind of chip for now, max6650). A zero kind means that
+         * the driver was loaded with the force parameter, the detection
+         * step shall be skipped. A positive kind means that the driver
+         * was loaded with the force parameter and a given kind of chip is
+         * requested, so both the detection and the identification steps
+         * are skipped.
+         *
+         * Currently I can find no way to distinguish between a MAX6650 and
+         * a MAX6651. This driver has only been tried on the former.
+         */
+
+        if ((kind < 0) &&
+           (  (i2c_smbus_read_byte_data(client, MAX6650_REG_CONFIG) & 0xC0)
+            ||(i2c_smbus_read_byte_data(client, MAX6650_REG_GPIO_STAT) & 0xE0)
+            ||(i2c_smbus_read_byte_data(client, MAX6650_REG_ALARM_EN) & 0xE0)
+            ||(i2c_smbus_read_byte_data(client, MAX6650_REG_ALARM) & 0xE0)
+            ||(i2c_smbus_read_byte_data(client, MAX6650_REG_COUNT) & 0xFC))) {
+                dev_dbg(&adapter->dev,
+                        "max6650: detection failed at 0x%02x.\n", address);
+                goto err_free;
+        }
+
+        dev_info(&adapter->dev, "max6650: chip found at 0x%02x.\n", address);
+
+        strlcpy(client->name, "max6650", I2C_NAME_SIZE);
+        mutex_init(&data->update_lock);
+
+        if ((err = i2c_attach_client(client))) {
+                dev_err(&adapter->dev, "max6650: failed to attach client.\n");
+                goto err_free;
+        }
+
+        /*
+         * Initialize the max6650 chip
+         */
+        if (max6650_init_client(client))
+                goto err_detach;
+
+        err = sysfs_create_group(&client->dev.kobj, &max6650_attr_grp);
+        if (err)
+                goto err_detach;
+
+        data->class_dev = hwmon_device_register(&client->dev);
+        if (!IS_ERR(data->class_dev))
+                return 0;
+
+        err = PTR_ERR(data->class_dev);
+        dev_err(&client->dev, "error registering hwmon device.\n");
+        sysfs_remove_group(&client->dev.kobj, &max6650_attr_grp);
+err_detach:
+        i2c_detach_client(client);
+err_free:
+        kfree(data);
+        return err;
+}
+
+static int max6650_detach_client(struct i2c_client *client)
+{
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int err;
+
+        sysfs_remove_group(&client->dev.kobj, &max6650_attr_grp);
+        hwmon_device_unregister(data->class_dev);
+        err = i2c_detach_client(client);
+        if (!err)
+                kfree(data);
+        return err;
+}
+
+static int max6650_init_client(struct i2c_client *client)
+{
+        struct max6650_data *data = i2c_get_clientdata(client);
+        int config;
+        int err = -EIO;
+
+        config = i2c_smbus_read_byte_data(client, MAX6650_REG_CONFIG);
+
+        if (config < 0) {
+                dev_err(&client->dev, "Error reading config, aborting.\n");
+                return err;
+        }
+
+        switch (fan_voltage) {
+                case 0:
+                        break;
+                case 5:
+                        config &= ~MAX6650_CFG_V12;
+                        break;
+                case 12:
+                        config |= MAX6650_CFG_V12;
+                        break;
+                default:
+                        dev_err(&client->dev,
+                                "illegal value for fan_voltage (%d)\n",
+                                fan_voltage);
+        }
+
+        dev_info(&client->dev, "Fan voltage is set to %dV.\n",
+                 (config & MAX6650_CFG_V12) ? 12 : 5);
+
+        switch (prescaler) {
+                case 0:
+                        break;
+                case 1:
+                        config &= ~MAX6650_CFG_PRESCALER_MASK;
+                        break;
+                case 2:
+                        config = (config & ~MAX6650_CFG_PRESCALER_MASK)
+                                 | MAX6650_CFG_PRESCALER_2;
+                        break;
+                case  4:
+                        config = (config & ~MAX6650_CFG_PRESCALER_MASK)
+                                 | MAX6650_CFG_PRESCALER_4;
+                        break;
+                case  8:
+                        config = (config & ~MAX6650_CFG_PRESCALER_MASK)
+                                 | MAX6650_CFG_PRESCALER_8;
+                        break;
+                case 16:
+                        config = (config & ~MAX6650_CFG_PRESCALER_MASK)
+                                 | MAX6650_CFG_PRESCALER_16;
+                        break;
+                default:
+                        dev_err(&client->dev,
+                                "illegal value for prescaler (%d)\n",
+                                prescaler);
+        }
+
+        dev_info(&client->dev, "Prescaler is set to %d.\n",
+                 1 << (config & MAX6650_CFG_PRESCALER_MASK));
+
+        /* If mode is set to "full off", we change it to "open loop" and
+         * set DAC to 255, which has the same effect. We do this because
+         * there's no "full off" mode defined in hwmon specifcations.
+         */
+
+        if ((config & MAX6650_CFG_MODE_MASK) == MAX6650_CFG_MODE_OFF) {
+                dev_dbg(&client->dev, "Change mode to open loop, full off.\n");
+                config = (config & ~MAX6650_CFG_MODE_MASK)
+                         | MAX6650_CFG_MODE_OPEN_LOOP;
+                if (i2c_smbus_write_byte_data(client, MAX6650_REG_DAC, 255)) {
+                        dev_err(&client->dev, "DAC write error, aborting.\n");
+                        return err;
+                }
+        }
+
+        if (i2c_smbus_write_byte_data(client, MAX6650_REG_CONFIG, config)) {
+                dev_err(&client->dev, "Config write error, aborting.\n");
+                return err;
+        }
+
+        data->config = config;
+        data->count = i2c_smbus_read_byte_data(client, MAX6650_REG_COUNT);
+
+        return 0;
+}
+
+static const u8 tach_reg[] = {
+        MAX6650_REG_TACH0,
+        MAX6650_REG_TACH1,
+        MAX6650_REG_TACH2,
+        MAX6650_REG_TACH3,
+};
+
+static struct max6650_data *max6650_update_device(struct device *dev)
+{
+        int i;
+        struct i2c_client *client = to_i2c_client(dev);
+        struct max6650_data *data = i2c_get_clientdata(client);
+
+        mutex_lock(&data->update_lock);
+
+        if (time_after(jiffies, data->last_updated + HZ) || !data->valid) {
+                data->speed = i2c_smbus_read_byte_data(client,
+                                                       MAX6650_REG_SPEED);
+                data->config = i2c_smbus_read_byte_data(client,
+                                                        MAX6650_REG_CONFIG);
+                for (i = 0; i < 4; i++) {
+                        data->tach[i] = i2c_smbus_read_byte_data(client,
+                                                                 tach_reg[i]);
+                }
+                data->count = i2c_smbus_read_byte_data(client,
+                                                        MAX6650_REG_COUNT);
+                data->dac = i2c_smbus_read_byte_data(client, MAX6650_REG_DAC);
+
+                data->last_updated = jiffies;
+                data->valid = 1;
+        }
+
+        mutex_unlock(&data->update_lock);
+
+        return data;
+}
+
+static int __init sensors_max6650_init(void)
+{
+        return i2c_add_driver(&max6650_driver);
+}
+
+static void __exit sensors_max6650_exit(void)
+{
+        i2c_del_driver(&max6650_driver);
+}
+
+MODULE_AUTHOR("Hans J. Koch");
+MODULE_DESCRIPTION("MAX6650 sensor driver");
+MODULE_LICENSE("GPL");
+
+module_init(sensors_max6650_init);
+module_exit(sensors_max6650_exit);