hwmon: new driver for ST stts751 thermal sensor

This patch adds a HWMON driver for ST Microelectronics STTS751
temperature sensors.

Thanks-to: LABBE Corentin [for suggestions]
Thanks-to: Guenter Roeck [for suggestion and discussions]
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Cc: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

3 files changed, 845 insertions, 0 deletions

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 190d270b20a2..0649d53f3d16 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1459,6 +1459,16 @@ config SENSORS_SCH5636
           This driver can also be built as a module.  If so, the module
           will be called sch5636.
 
+config SENSORS_STTS751
+        tristate "ST Microelectronics STTS751"
+        depends on I2C
+        help
+          If you say yes here you get support for STTS751
+          temperature sensor chips.
+
+          This driver can also be built as a module.  If so, the module
+          will be called stts751.
+
 config SENSORS_SMM665
         tristate "Summit Microelectronics SMM665"
         depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index d2cb7e804a0f..5509edf6186a 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -148,6 +148,7 @@ obj-$(CONFIG_SENSORS_SMM665)	+= smm665.o
 obj-$(CONFIG_SENSORS_SMSC47B397)+= smsc47b397.o
 obj-$(CONFIG_SENSORS_SMSC47M1)  += smsc47m1.o
 obj-$(CONFIG_SENSORS_SMSC47M192)+= smsc47m192.o
+obj-$(CONFIG_SENSORS_STTS751)   += stts751.o
 obj-$(CONFIG_SENSORS_AMC6821)   += amc6821.o
 obj-$(CONFIG_SENSORS_TC74)      += tc74.o
 obj-$(CONFIG_SENSORS_THMC50)    += thmc50.o
diff --git a/drivers/hwmon/stts751.c b/drivers/hwmon/stts751.c
new file mode 100644
index 000000000000..55450680fb58
--- /dev/null
+++ b/drivers/hwmon/stts751.c
@@ -0,0 +1,834 @@
+/*
+ * STTS751 sensor driver
+ *
+ * Copyright (C) 2016-2017 Istituto Italiano di Tecnologia - RBCS - EDL
+ * Robotics, Brain and Cognitive Sciences department
+ * Electronic Design Laboratory
+ *
+ * Written by Andrea Merello <andrea.merello@gmail.com>
+ *
+ * Based on  LM95241 driver and LM90 driver
+ *
+ * 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.
+ */
+
+#include <linux/bitops.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+#include <linux/util_macros.h>
+
+#define DEVNAME "stts751"
+
+static const unsigned short normal_i2c[] = {
+        0x48, 0x49, 0x38, 0x39,  /* STTS751-0 */
+        0x4A, 0x4B, 0x3A, 0x3B,  /* STTS751-1 */
+        I2C_CLIENT_END };
+
+#define STTS751_REG_TEMP_H      0x00
+#define STTS751_REG_STATUS      0x01
+#define STTS751_STATUS_TRIPT    BIT(0)
+#define STTS751_STATUS_TRIPL    BIT(5)
+#define STTS751_STATUS_TRIPH    BIT(6)
+#define STTS751_REG_TEMP_L      0x02
+#define STTS751_REG_CONF        0x03
+#define STTS751_CONF_RES_MASK   0x0C
+#define STTS751_CONF_RES_SHIFT  2
+#define STTS751_CONF_EVENT_DIS  BIT(7)
+#define STTS751_CONF_STOP       BIT(6)
+#define STTS751_REG_RATE        0x04
+#define STTS751_REG_HLIM_H      0x05
+#define STTS751_REG_HLIM_L      0x06
+#define STTS751_REG_LLIM_H      0x07
+#define STTS751_REG_LLIM_L      0x08
+#define STTS751_REG_TLIM        0x20
+#define STTS751_REG_HYST        0x21
+#define STTS751_REG_SMBUS_TO    0x22
+
+#define STTS751_REG_PROD_ID     0xFD
+#define STTS751_REG_MAN_ID      0xFE
+#define STTS751_REG_REV_ID      0xFF
+
+#define STTS751_0_PROD_ID       0x00
+#define STTS751_1_PROD_ID       0x01
+#define ST_MAN_ID               0x53
+
+/*
+ * Possible update intervals are (in mS):
+ * 16000, 8000, 4000, 2000, 1000, 500, 250, 125, 62.5, 31.25
+ * However we are not going to complicate things too much and we stick to the
+ * approx value in mS.
+ */
+static const int stts751_intervals[] = {
+        16000, 8000, 4000, 2000, 1000, 500, 250, 125, 63, 31
+};
+
+static const struct i2c_device_id stts751_id[] = {
+        { "stts751", 0 },
+        { }
+};
+
+struct stts751_priv {
+        struct device *dev;
+        struct i2c_client *client;
+        struct mutex access_lock;
+        u8 interval;
+        int res;
+        int event_max, event_min;
+        int therm;
+        int hyst;
+        bool smbus_timeout;
+        int temp;
+        unsigned long last_update, last_alert_update;
+        u8 config;
+        bool min_alert, max_alert, therm_trip;
+        bool data_valid, alert_valid;
+        bool notify_max, notify_min;
+};
+
+/*
+ * These functions converts temperature from HW format to integer format and
+ * vice-vers. They are (mostly) taken from lm90 driver. Unit is in mC.
+ */
+static int stts751_to_deg(s16 hw_val)
+{
+        return hw_val * 125 / 32;
+}
+
+static s32 stts751_to_hw(int val)
+{
+        return DIV_ROUND_CLOSEST(val, 125) * 32;
+}
+
+static int stts751_adjust_resolution(struct stts751_priv *priv)
+{
+        u8 res;
+
+        switch (priv->interval) {
+        case 9:
+                /* 10 bits */
+                res = 0;
+                break;
+        case 8:
+                /* 11 bits */
+                res = 1;
+                break;
+        default:
+                /* 12 bits */
+                res = 3;
+                break;
+        }
+
+        if (priv->res == res)
+                return 0;
+
+        priv->config &= ~STTS751_CONF_RES_MASK;
+        priv->config |= res << STTS751_CONF_RES_SHIFT;
+        dev_dbg(&priv->client->dev, "setting res %d. config %x",
+                res, priv->config);
+        priv->res = res;
+
+        return i2c_smbus_write_byte_data(priv->client,
+                                STTS751_REG_CONF, priv->config);
+}
+
+static int stts751_update_temp(struct stts751_priv *priv)
+{
+        s32 integer1, integer2, frac;
+
+        /*
+         * There is a trick here, like in the lm90 driver. We have to read two
+         * registers to get the sensor temperature, but we have to beware a
+         * conversion could occur between the readings. We could use the
+         * one-shot conversion register, but we don't want to do this (disables
+         * hardware monitoring). So the solution used here is to read the high
+         * byte once, then the low byte, then the high byte again. If the new
+         * high byte matches the old one, then we have a valid reading. Else we
+         * have to read the low byte again, and now we believe we have a correct
+         * reading.
+         */
+        integer1 = i2c_smbus_read_byte_data(priv->client, STTS751_REG_TEMP_H);
+        if (integer1 < 0) {
+                dev_dbg(&priv->client->dev,
+                        "I2C read failed (temp H). ret: %x\n", integer1);
+                return integer1;
+        }
+
+        frac = i2c_smbus_read_byte_data(priv->client, STTS751_REG_TEMP_L);
+        if (frac < 0) {
+                dev_dbg(&priv->client->dev,
+                        "I2C read failed (temp L). ret: %x\n", frac);
+                return frac;
+        }
+
+        integer2 = i2c_smbus_read_byte_data(priv->client, STTS751_REG_TEMP_H);
+        if (integer2 < 0) {
+                dev_dbg(&priv->client->dev,
+                        "I2C 2nd read failed (temp H). ret: %x\n", integer2);
+                return integer2;
+        }
+
+        if (integer1 != integer2) {
+                frac = i2c_smbus_read_byte_data(priv->client,
+                                                STTS751_REG_TEMP_L);
+                if (frac < 0) {
+                        dev_dbg(&priv->client->dev,
+                                "I2C 2nd read failed (temp L). ret: %x\n",
+                                frac);
+                        return frac;
+                }
+        }
+
+        priv->temp = stts751_to_deg((integer1 << 8) | frac);
+        return 0;
+}
+
+static int stts751_set_temp_reg16(struct stts751_priv *priv, int temp,
+                                  u8 hreg, u8 lreg)
+{
+        s32 hwval;
+        int ret;
+
+        hwval = stts751_to_hw(temp);
+
+        ret = i2c_smbus_write_byte_data(priv->client, hreg, hwval >> 8);
+        if (ret)
+                return ret;
+
+        return i2c_smbus_write_byte_data(priv->client, lreg, hwval & 0xff);
+}
+
+static int stts751_set_temp_reg8(struct stts751_priv *priv, int temp, u8 reg)
+{
+        s32 hwval;
+
+        hwval = stts751_to_hw(temp);
+        return i2c_smbus_write_byte_data(priv->client, reg, hwval >> 8);
+}
+
+static int stts751_read_reg16(struct stts751_priv *priv, int *temp,
+                              u8 hreg, u8 lreg)
+{
+        int integer, frac;
+
+        integer = i2c_smbus_read_byte_data(priv->client, hreg);
+        if (integer < 0)
+                return integer;
+
+        frac = i2c_smbus_read_byte_data(priv->client, lreg);
+        if (frac < 0)
+                return frac;
+
+        *temp = stts751_to_deg((integer << 8) | frac);
+
+        return 0;
+}
+
+static int stts751_read_reg8(struct stts751_priv *priv, int *temp, u8 reg)
+{
+        int integer;
+
+        integer = i2c_smbus_read_byte_data(priv->client, reg);
+        if (integer < 0)
+                return integer;
+
+        *temp = stts751_to_deg(integer << 8);
+
+        return 0;
+}
+
+/*
+ * Update alert flags without waiting for cache to expire. We detects alerts
+ * immediately for the sake of the alert handler; we still need to deal with
+ * caching to workaround the fact that alarm flags int the status register,
+ * despite what the datasheet claims, gets always cleared on read.
+ */
+static int stts751_update_alert(struct stts751_priv *priv)
+{
+        int ret;
+        bool conv_done;
+        int cache_time = msecs_to_jiffies(stts751_intervals[priv->interval]);
+
+        /*
+         * Add another 10% because if we run faster than the HW conversion
+         * rate we will end up in reporting incorrectly alarms.
+         */
+        cache_time += cache_time / 10;
+
+        ret = i2c_smbus_read_byte_data(priv->client, STTS751_REG_STATUS);
+        if (ret < 0)
+                return ret;
+
+        dev_dbg(&priv->client->dev, "status reg %x\n", ret);
+        conv_done = ret & (STTS751_STATUS_TRIPH | STTS751_STATUS_TRIPL);
+        /*
+         * Reset the cache if the cache time expired, or if we are sure
+         * we have valid data from a device conversion, or if we know
+         * our cache has been never written.
+         *
+         * Note that when the cache has been never written the point is
+         * to correctly initialize the timestamp, rather than clearing
+         * the cache values.
+         *
+         * Note that updating the cache timestamp when we get an alarm flag
+         * is required, otherwise we could incorrectly report alarms to be zero.
+         */
+        if (time_after(jiffies, priv->last_alert_update + cache_time) ||
+            conv_done || !priv->alert_valid) {
+                priv->max_alert = false;
+                priv->min_alert = false;
+                priv->alert_valid = true;
+                priv->last_alert_update = jiffies;
+                dev_dbg(&priv->client->dev, "invalidating alert cache\n");
+        }
+
+        priv->max_alert |= !!(ret & STTS751_STATUS_TRIPH);
+        priv->min_alert |= !!(ret & STTS751_STATUS_TRIPL);
+        priv->therm_trip = !!(ret & STTS751_STATUS_TRIPT);
+
+        dev_dbg(&priv->client->dev, "max_alert: %d, min_alert: %d, therm_trip: %d\n",
+                priv->max_alert, priv->min_alert, priv->therm_trip);
+
+        return 0;
+}
+
+static void stts751_alert(struct i2c_client *client,
+                          enum i2c_alert_protocol type, unsigned int data)
+{
+        int ret;
+        struct stts751_priv *priv = i2c_get_clientdata(client);
+
+        if (type != I2C_PROTOCOL_SMBUS_ALERT)
+                return;
+
+        dev_dbg(&client->dev, "alert!");
+
+        mutex_lock(&priv->access_lock);
+        ret = stts751_update_alert(priv);
+        if (ret < 0) {
+                /* default to worst case */
+                priv->max_alert = true;
+                priv->min_alert = true;
+
+                dev_warn(priv->dev,
+                         "Alert received, but can't communicate to the device. Triggering all alarms!");
+        }
+
+        if (priv->max_alert) {
+                if (priv->notify_max)
+                        dev_notice(priv->dev, "got alert for HIGH temperature");
+                priv->notify_max = false;
+
+                /* unblock alert poll */
+                sysfs_notify(&priv->dev->kobj, NULL, "temp1_max_alarm");
+        }
+
+        if (priv->min_alert) {
+                if (priv->notify_min)
+                        dev_notice(priv->dev, "got alert for LOW temperature");
+                priv->notify_min = false;
+
+                /* unblock alert poll */
+                sysfs_notify(&priv->dev->kobj, NULL, "temp1_min_alarm");
+        }
+
+        if (priv->min_alert || priv->max_alert)
+                kobject_uevent(&priv->dev->kobj, KOBJ_CHANGE);
+
+        mutex_unlock(&priv->access_lock);
+}
+
+static int stts751_update(struct stts751_priv *priv)
+{
+        int ret;
+        int cache_time = msecs_to_jiffies(stts751_intervals[priv->interval]);
+
+        if (time_after(jiffies, priv->last_update + cache_time) ||
+            !priv->data_valid) {
+                ret = stts751_update_temp(priv);
+                if (ret)
+                        return ret;
+
+                ret = stts751_update_alert(priv);
+                if (ret)
+                        return ret;
+                priv->data_valid = true;
+                priv->last_update = jiffies;
+        }
+
+        return 0;
+}
+
+static ssize_t show_max_alarm(struct device *dev, struct device_attribute *attr,
+                              char *buf)
+{
+        int ret;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        mutex_lock(&priv->access_lock);
+        ret = stts751_update(priv);
+        if (!ret)
+                priv->notify_max = true;
+        mutex_unlock(&priv->access_lock);
+        if (ret < 0)
+                return ret;
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->max_alert);
+}
+
+static ssize_t show_min_alarm(struct device *dev, struct device_attribute *attr,
+                              char *buf)
+{
+        int ret;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        mutex_lock(&priv->access_lock);
+        ret = stts751_update(priv);
+        if (!ret)
+                priv->notify_min = true;
+        mutex_unlock(&priv->access_lock);
+        if (ret < 0)
+                return ret;
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->min_alert);
+}
+
+static ssize_t show_input(struct device *dev, struct device_attribute *attr,
+                          char *buf)
+{
+        int ret;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        mutex_lock(&priv->access_lock);
+        ret = stts751_update(priv);
+        mutex_unlock(&priv->access_lock);
+        if (ret < 0)
+                return ret;
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->temp);
+}
+
+static ssize_t show_therm(struct device *dev, struct device_attribute *attr,
+                          char *buf)
+{
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->therm);
+}
+
+static ssize_t set_therm(struct device *dev, struct device_attribute *attr,
+                         const char *buf, size_t count)
+{
+        int ret;
+        long temp;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        if (kstrtol(buf, 10, &temp) < 0)
+                return -EINVAL;
+
+        /* HW works in range -64C to +127.937C */
+        temp = clamp_val(temp, -64000, 127937);
+        mutex_lock(&priv->access_lock);
+        ret = stts751_set_temp_reg8(priv, temp, STTS751_REG_TLIM);
+        if (ret)
+                goto exit;
+
+        dev_dbg(&priv->client->dev, "setting therm %ld", temp);
+
+        /*
+         * hysteresis reg is relative to therm, so the HW does not need to be
+         * adjusted, we need to update our local copy only.
+         */
+        priv->hyst = temp - (priv->therm - priv->hyst);
+        priv->therm = temp;
+
+exit:
+        mutex_unlock(&priv->access_lock);
+        if (ret)
+                return ret;
+
+        return count;
+}
+
+static ssize_t show_hyst(struct device *dev, struct device_attribute *attr,
+                         char *buf)
+{
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->hyst);
+}
+
+static ssize_t set_hyst(struct device *dev, struct device_attribute *attr,
+                        const char *buf, size_t count)
+{
+        int ret;
+        long temp;
+
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        if (kstrtol(buf, 10, &temp) < 0)
+                return -EINVAL;
+
+        mutex_lock(&priv->access_lock);
+        /* HW works in range -64C to +127.937C */
+        temp = clamp_val(temp, -64000, priv->therm);
+        priv->hyst = temp;
+        dev_dbg(&priv->client->dev, "setting hyst %ld", temp);
+        temp = priv->therm - temp;
+        ret = stts751_set_temp_reg8(priv, temp, STTS751_REG_HYST);
+        mutex_unlock(&priv->access_lock);
+        if (ret)
+                return ret;
+
+        return count;
+}
+
+static ssize_t show_therm_trip(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+        int ret;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        mutex_lock(&priv->access_lock);
+        ret = stts751_update(priv);
+        mutex_unlock(&priv->access_lock);
+        if (ret < 0)
+                return ret;
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->therm_trip);
+}
+
+static ssize_t show_max(struct device *dev, struct device_attribute *attr,
+                        char *buf)
+{
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->event_max);
+}
+
+static ssize_t set_max(struct device *dev, struct device_attribute *attr,
+                       const char *buf, size_t count)
+{
+        int ret;
+        long temp;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        if (kstrtol(buf, 10, &temp) < 0)
+                return -EINVAL;
+
+        mutex_lock(&priv->access_lock);
+        /* HW works in range -64C to +127.937C */
+        temp = clamp_val(temp, priv->event_min, 127937);
+        ret = stts751_set_temp_reg16(priv, temp,
+                                     STTS751_REG_HLIM_H, STTS751_REG_HLIM_L);
+        if (ret)
+                goto exit;
+
+        dev_dbg(&priv->client->dev, "setting event max %ld", temp);
+        priv->event_max = temp;
+        ret = count;
+exit:
+        mutex_unlock(&priv->access_lock);
+        return ret;
+}
+
+static ssize_t show_min(struct device *dev, struct device_attribute *attr,
+                        char *buf)
+{
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n", priv->event_min);
+}
+
+static ssize_t set_min(struct device *dev, struct device_attribute *attr,
+                       const char *buf, size_t count)
+{
+        int ret;
+        long temp;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        if (kstrtol(buf, 10, &temp) < 0)
+                return -EINVAL;
+
+        mutex_lock(&priv->access_lock);
+        /* HW works in range -64C to +127.937C */
+        temp = clamp_val(temp, -64000, priv->event_max);
+        ret = stts751_set_temp_reg16(priv, temp,
+                                     STTS751_REG_LLIM_H, STTS751_REG_LLIM_L);
+        if (ret)
+                goto exit;
+
+        dev_dbg(&priv->client->dev, "setting event min %ld", temp);
+        priv->event_min = temp;
+        ret = count;
+exit:
+        mutex_unlock(&priv->access_lock);
+        return ret;
+}
+
+static ssize_t show_interval(struct device *dev, struct device_attribute *attr,
+                             char *buf)
+{
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        return snprintf(buf, PAGE_SIZE - 1, "%d\n",
+                        stts751_intervals[priv->interval]);
+}
+
+static ssize_t set_interval(struct device *dev, struct device_attribute *attr,
+                            const char *buf, size_t count)
+{
+        unsigned long val;
+        int idx;
+        int ret = count;
+        struct stts751_priv *priv = dev_get_drvdata(dev);
+
+        if (kstrtoul(buf, 10, &val) < 0)
+                return -EINVAL;
+
+        idx = find_closest_descending(val, stts751_intervals,
+                                      ARRAY_SIZE(stts751_intervals));
+
+        dev_dbg(&priv->client->dev, "setting interval. req:%lu, idx: %d, val: %d",
+                val, idx, stts751_intervals[idx]);
+
+        mutex_lock(&priv->access_lock);
+        if (priv->interval == idx)
+                goto exit;
+
+        /*
+         * In early development stages I've become suspicious about the chip
+         * starting to misbehave if I ever set, even briefly, an invalid
+         * configuration. While I'm not sure this is really needed, be
+         * conservative and set rate/resolution in such an order that avoids
+         * passing through an invalid configuration.
+         */
+
+        /* speed up: lower the resolution, then modify convrate */
+        if (priv->interval < idx) {
+                dev_dbg(&priv->client->dev, "lower resolution, then modify convrate");
+                priv->interval = idx;
+                ret = stts751_adjust_resolution(priv);
+                if (ret)
+                        goto exit;
+        }
+
+        ret = i2c_smbus_write_byte_data(priv->client, STTS751_REG_RATE, idx);
+        if (ret)
+                goto exit;
+        /* slow down: modify convrate, then raise resolution */
+        if (priv->interval != idx) {
+                dev_dbg(&priv->client->dev, "modify convrate, then raise resolution");
+                priv->interval = idx;
+                ret = stts751_adjust_resolution(priv);
+                if (ret)
+                        goto exit;
+        }
+        ret = count;
+exit:
+        mutex_unlock(&priv->access_lock);
+
+        return ret;
+}
+
+static int stts751_detect(struct i2c_client *new_client,
+                          struct i2c_board_info *info)
+{
+        struct i2c_adapter *adapter = new_client->adapter;
+        const char *name;
+        int tmp;
+
+        if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+                return -ENODEV;
+
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_MAN_ID);
+        if (tmp != ST_MAN_ID)
+                return -ENODEV;
+
+        /* lower temperaure registers always have bits 0-3 set to zero */
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_TEMP_L);
+        if (tmp & 0xf)
+                return -ENODEV;
+
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_HLIM_L);
+        if (tmp & 0xf)
+                return -ENODEV;
+
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_LLIM_L);
+        if (tmp & 0xf)
+                return -ENODEV;
+
+        /* smbus timeout register always have bits 0-7 set to zero */
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_SMBUS_TO);
+        if (tmp & 0x7f)
+                return -ENODEV;
+
+        tmp = i2c_smbus_read_byte_data(new_client, STTS751_REG_PROD_ID);
+
+        switch (tmp) {
+        case STTS751_0_PROD_ID:
+                name = "STTS751-0";
+                break;
+        case STTS751_1_PROD_ID:
+                name = "STTS751-1";
+                break;
+        default:
+                return -ENODEV;
+        }
+        dev_dbg(&new_client->dev, "Chip %s detected", name);
+
+        strlcpy(info->type, stts751_id[0].name, I2C_NAME_SIZE);
+        return 0;
+}
+
+static int stts751_read_chip_config(struct stts751_priv *priv)
+{
+        int ret;
+        int tmp;
+
+        ret = i2c_smbus_read_byte_data(priv->client, STTS751_REG_CONF);
+        if (ret < 0)
+                return ret;
+        priv->config = ret;
+        priv->res = (ret & STTS751_CONF_RES_MASK) >> STTS751_CONF_RES_SHIFT;
+
+        ret = i2c_smbus_read_byte_data(priv->client, STTS751_REG_RATE);
+        if (ret < 0)
+                return ret;
+        priv->interval = ret;
+
+        ret = stts751_read_reg16(priv, &priv->event_max,
+                                 STTS751_REG_HLIM_H, STTS751_REG_HLIM_L);
+        if (ret)
+                return ret;
+
+        ret = stts751_read_reg16(priv, &priv->event_min,
+                                 STTS751_REG_LLIM_H, STTS751_REG_LLIM_L);
+        if (ret)
+                return ret;
+
+        ret = stts751_read_reg8(priv, &priv->therm, STTS751_REG_TLIM);
+        if (ret)
+                return ret;
+
+        ret = stts751_read_reg8(priv, &tmp, STTS751_REG_HYST);
+        if (ret)
+                return ret;
+        priv->hyst = priv->therm - tmp;
+
+        return 0;
+}
+
+static SENSOR_DEVICE_ATTR(temp1_input, 0444, show_input, NULL, 0);
+static SENSOR_DEVICE_ATTR(temp1_min, 0644, show_min, set_min, 0);
+static SENSOR_DEVICE_ATTR(temp1_max, 0644, show_max, set_max, 0);
+static SENSOR_DEVICE_ATTR(temp1_min_alarm, 0444, show_min_alarm, NULL, 0);
+static SENSOR_DEVICE_ATTR(temp1_max_alarm, 0444, show_max_alarm, NULL, 0);
+static SENSOR_DEVICE_ATTR(temp1_crit, 0644, show_therm, set_therm, 0);
+static SENSOR_DEVICE_ATTR(temp1_crit_hyst, 0644, show_hyst, set_hyst, 0);
+static SENSOR_DEVICE_ATTR(temp1_crit_alarm, 0444, show_therm_trip, NULL, 0);
+static SENSOR_DEVICE_ATTR(update_interval, 0644,
+                          show_interval, set_interval, 0);
+
+static struct attribute *stts751_attrs[] = {
+        &sensor_dev_attr_temp1_input.dev_attr.attr,
+        &sensor_dev_attr_temp1_min.dev_attr.attr,
+        &sensor_dev_attr_temp1_max.dev_attr.attr,
+        &sensor_dev_attr_temp1_min_alarm.dev_attr.attr,
+        &sensor_dev_attr_temp1_max_alarm.dev_attr.attr,
+        &sensor_dev_attr_temp1_crit.dev_attr.attr,
+        &sensor_dev_attr_temp1_crit_hyst.dev_attr.attr,
+        &sensor_dev_attr_temp1_crit_alarm.dev_attr.attr,
+        &sensor_dev_attr_update_interval.dev_attr.attr,
+        NULL
+};
+ATTRIBUTE_GROUPS(stts751);
+
+static int stts751_probe(struct i2c_client *client,
+                         const struct i2c_device_id *id)
+{
+        struct stts751_priv *priv;
+        int ret;
+        bool smbus_nto;
+        int rev_id;
+
+        priv = devm_kzalloc(&client->dev, sizeof(*priv), GFP_KERNEL);
+        if (!priv)
+                return -ENOMEM;
+
+        priv->client = client;
+        priv->notify_max = true;
+        priv->notify_min = true;
+        i2c_set_clientdata(client, priv);
+        mutex_init(&priv->access_lock);
+
+        if (device_property_present(&client->dev,
+                                    "smbus-timeout-disable")) {
+                smbus_nto = device_property_read_bool(&client->dev,
+                                                      "smbus-timeout-disable");
+
+                ret = i2c_smbus_write_byte_data(client, STTS751_REG_SMBUS_TO,
+                                                smbus_nto ? 0 : 0x80);
+                if (ret)
+                        return ret;
+        }
+
+        rev_id = i2c_smbus_read_byte_data(client, STTS751_REG_REV_ID);
+        if (rev_id < 0)
+                return -ENODEV;
+        if (rev_id != 0x1) {
+                dev_dbg(&client->dev, "Chip revision 0x%x is untested\n",
+                        rev_id);
+        }
+
+        ret = stts751_read_chip_config(priv);
+        if (ret)
+                return ret;
+
+        priv->config &= ~(STTS751_CONF_STOP | STTS751_CONF_EVENT_DIS);
+        ret = i2c_smbus_write_byte_data(client, STTS751_REG_CONF, priv->config);
+        if (ret)
+                return ret;
+
+        priv->dev = devm_hwmon_device_register_with_groups(&client->dev,
+                                                        client->name, priv,
+                                                        stts751_groups);
+        return PTR_ERR_OR_ZERO(priv->dev);
+}
+
+MODULE_DEVICE_TABLE(i2c, stts751_id);
+
+static struct i2c_driver stts751_driver = {
+        .class          = I2C_CLASS_HWMON,
+        .driver = {
+                .name   = DEVNAME,
+        },
+        .probe          = stts751_probe,
+        .id_table       = stts751_id,
+        .detect         = stts751_detect,
+        .alert          = stts751_alert,
+        .address_list   = normal_i2c,
+};
+
+module_i2c_driver(stts751_driver);
+
+MODULE_AUTHOR("Andrea Merello <andrea.merello@gmail.com>");
+MODULE_DESCRIPTION("STTS751 sensor driver");
+MODULE_LICENSE("GPL");