hwmon: (sht15) add support for the status register

* Add support for:
  - Heater.
  - End of battery notice.
  - Ability not to reload from OTP.
  - Low resolution (12bit temp, 8bit humidity).
* Add an utility function to read individual bytes from the device.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

3 files changed, 245 insertions, 35 deletions

diff --git a/Documentation/hwmon/sht15 b/Documentation/hwmon/sht15
index 2919c516fdbc..d1939b25eb16 100644
--- a/Documentation/hwmon/sht15
+++ b/Documentation/hwmon/sht15
@@ -4,6 +4,7 @@ Kernel driver sht15
 Authors:
   * Wouter Horre
   * Jonathan Cameron
+  * Vivien Didelot <vivien.didelot@savoirfairelinux.com>
 
 Supported chips:
   * Sensirion SHT10
@@ -30,13 +31,37 @@ Description
 The SHT10, SHT11, SHT15, SHT71, and SHT75 are humidity and temperature
 sensors.
 
-The devices communicate using two GPIO lines and use the default
-resolution settings of 14 bits for temperature and 12 bits for humidity.
+The devices communicate using two GPIO lines.
+
+Supported resolutions for the measurements are 14 bits for temperature and 12
+bits for humidity, or 12 bits for temperature and 8 bits for humidity.
+
+The humidity calibration coefficients are programmed into an OTP memory on the
+chip. These coefficients are used to internally calibrate the signals from the
+sensors. Disabling the reload of those coefficients allows saving 10ms for each
+measurement and decrease power consumption, while loosing on precision.
+
+Some options may be set directly in the sht15_platform_data structure
+or via sysfs attributes.
 
 Note: The regulator supply name is set to "vcc".
 
+Platform data
+-------------
+
+* no_otp_reload:
+  flag to indicate not to reload from OTP (default to false).
+* low_resolution:
+  flag to indicate the temp/humidity resolution to use (default to false).
+
 Sysfs interface
 ---------------
 
 * temp1_input:     temperature input
 * humidity1_input: humidity input
+* heater_enable:   write 1 in this attribute to enable the on-chip heater,
+                   0 to disable it. Be careful not to enable the heater
+                   for too long.
+* temp1_fault:     if 1, this means that the voltage is low (below 2.47V) and
+                   measurement may be invalid.
+* humidity1_fault: same as temp1_fault.
diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c
index 3182b3f578e2..49da089b5de9 100644
--- a/drivers/hwmon/sht15.c
+++ b/drivers/hwmon/sht15.c
@@ -1,6 +1,9 @@
 /*
  * sht15.c - support for the SHT15 Temperature and Humidity Sensor
  *
+ * Portions Copyright (c) 2010-2011 Savoir-faire Linux Inc.
+ *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>
+ *
  * Copyright (c) 2009 Jonathan Cameron
  *
  * Copyright (c) 2007 Wouter Horre
@@ -33,6 +36,8 @@
 /* Commands */
 #define SHT15_MEASURE_TEMP              0x03
 #define SHT15_MEASURE_RH                0x05
+#define SHT15_WRITE_STATUS              0x06
+#define SHT15_READ_STATUS               0x07
 #define SHT15_SOFT_RESET                0x1E
 
 /* Min timings */
@@ -41,6 +46,12 @@
 #define SHT15_TSU                       150     /* (nsecs) data setup time */
 #define SHT15_TSRST                     11      /* (msecs) soft reset time */
 
+/* Status Register Bits */
+#define SHT15_STATUS_LOW_RESOLUTION     0x01
+#define SHT15_STATUS_NO_OTP_RELOAD      0x02
+#define SHT15_STATUS_HEATER             0x04
+#define SHT15_STATUS_LOW_BATTERY        0x40
+
 /* Actions the driver may be doing */
 enum sht15_state {
         SHT15_READING_NOTHING,
@@ -74,9 +85,12 @@ static const struct sht15_temppair temppoints[] = {
  * @wait_queue:         wait queue for getting values from device.
  * @val_temp:           last temperature value read from device.
  * @val_humid:          last humidity value read from device.
+ * @val_status:         last status register value read from device.
  * @state:              state identifying the action the driver is doing.
  * @measurements_valid: are the current stored measures valid (start condition).
+ * @status_valid:       is the current stored status valid (start condition).
  * @last_measurement:   time of last measure.
+ * @last_status:        time of last status reading.
  * @read_lock:          mutex to ensure only one read in progress at a time.
  * @dev:                associate device structure.
  * @hwmon_dev:          device associated with hwmon subsystem.
@@ -97,9 +111,12 @@ struct sht15_data {
         wait_queue_head_t               wait_queue;
         uint16_t                        val_temp;
         uint16_t                        val_humid;
+        u8                              val_status;
         enum sht15_state                state;
         bool                            measurements_valid;
+        bool                            status_valid;
         unsigned long                   last_measurement;
+        unsigned long                   last_status;
         struct mutex                    read_lock;
         struct device                   *dev;
         struct device                   *hwmon_dev;
@@ -244,11 +261,106 @@ static int sht15_soft_reset(struct sht15_data *data)
         if (ret)
                 return ret;
         msleep(SHT15_TSRST);
+        /* device resets default hardware status register value */
+        data->val_status = 0;
+
+        return ret;
+}
+
+/**
+ * sht15_end_transmission() - notify device of end of transmission
+ * @data:       device state.
+ *
+ * This is basically a NAK (single clock pulse, data high).
+ */
+static void sht15_end_transmission(struct sht15_data *data)
+{
+        gpio_direction_output(data->pdata->gpio_data, 1);
+        ndelay(SHT15_TSU);
+        gpio_set_value(data->pdata->gpio_sck, 1);
+        ndelay(SHT15_TSCKH);
+        gpio_set_value(data->pdata->gpio_sck, 0);
+        ndelay(SHT15_TSCKL);
+}
+
+/**
+ * sht15_read_byte() - Read a byte back from the device
+ * @data:       device state.
+ */
+static u8 sht15_read_byte(struct sht15_data *data)
+{
+        int i;
+        u8 byte = 0;
+
+        for (i = 0; i < 8; ++i) {
+                byte <<= 1;
+                gpio_set_value(data->pdata->gpio_sck, 1);
+                ndelay(SHT15_TSCKH);
+                byte |= !!gpio_get_value(data->pdata->gpio_data);
+                gpio_set_value(data->pdata->gpio_sck, 0);
+                ndelay(SHT15_TSCKL);
+        }
+        return byte;
+}
+
+/**
+ * sht15_send_status() - write the status register byte
+ * @data:       sht15 specific data.
+ * @status:     the byte to set the status register with.
+ *
+ * As described in figure 14 and table 5 of the datasheet.
+ */
+static int sht15_send_status(struct sht15_data *data, u8 status)
+{
+        int ret;
+
+        ret = sht15_send_cmd(data, SHT15_WRITE_STATUS);
+        if (ret)
+                return ret;
+        gpio_direction_output(data->pdata->gpio_data, 1);
+        ndelay(SHT15_TSU);
+        sht15_send_byte(data, status);
+        ret = sht15_wait_for_response(data);
+        if (ret)
+                return ret;
 
+        data->val_status = status;
         return 0;
 }
 
 /**
+ * sht15_update_status() - get updated status register from device if too old
+ * @data:       device instance specific data.
+ *
+ * As described in figure 15 and table 5 of the datasheet.
+ */
+static int sht15_update_status(struct sht15_data *data)
+{
+        int ret = 0;
+        u8 status;
+        int timeout = HZ;
+
+        mutex_lock(&data->read_lock);
+        if (time_after(jiffies, data->last_status + timeout)
+                        || !data->status_valid) {
+                ret = sht15_send_cmd(data, SHT15_READ_STATUS);
+                if (ret)
+                        goto error_ret;
+                status = sht15_read_byte(data);
+
+                sht15_end_transmission(data);
+
+                data->val_status = status;
+                data->status_valid = true;
+                data->last_status = jiffies;
+        }
+error_ret:
+        mutex_unlock(&data->read_lock);
+
+        return ret;
+}
+
+/**
  * sht15_measurement() - get a new value from device
  * @data:               device instance specific data
  * @command:            command sent to request value
@@ -324,6 +436,7 @@ error_ret:
 static inline int sht15_calc_temp(struct sht15_data *data)
 {
         int d1 = temppoints[0].d1;
+        int d2 = (data->val_status & SHT15_STATUS_LOW_RESOLUTION) ? 40 : 10;
         int i;
 
         for (i = ARRAY_SIZE(temppoints) - 1; i > 0; i--)
@@ -336,7 +449,7 @@ static inline int sht15_calc_temp(struct sht15_data *data)
                         break;
                 }
 
-        return data->val_temp * 10 + d1;
+        return data->val_temp * d2 + d1;
 }
 
 /**
@@ -353,19 +466,86 @@ static inline int sht15_calc_humid(struct sht15_data *data)
 {
         int rh_linear; /* milli percent */
         int temp = sht15_calc_temp(data);
-
+        int c2, c3;
+        int t2;
         const int c1 = -4;
-        const int c2 = 40500; /* x 10 ^ -6 */
-        const int c3 = -28;   /* x 10 ^ -7 */
+
+        if (data->val_status & SHT15_STATUS_LOW_RESOLUTION) {
+                c2 = 648000; /* x 10 ^ -6 */
+                c3 = -7200;  /* x 10 ^ -7 */
+                t2 = 1280;
+        } else {
+                c2 = 40500;  /* x 10 ^ -6 */
+                c3 = -28;    /* x 10 ^ -7 */
+                t2 = 80;
+        }
 
         rh_linear = c1 * 1000
                 + c2 * data->val_humid / 1000
                 + (data->val_humid * data->val_humid * c3) / 10000;
-        return (temp - 25000) * (10000 + 80 * data->val_humid)
+        return (temp - 25000) * (10000 + t2 * data->val_humid)
                 / 1000000 + rh_linear;
 }
 
 /**
+ * sht15_show_status() - show status information in sysfs
+ * @dev:        device.
+ * @attr:       device attribute.
+ * @buf:        sysfs buffer where information is written to.
+ *
+ * Will be called on read access to temp1_fault, humidity1_fault
+ * and heater_enable sysfs attributes.
+ * Returns number of bytes written into buffer, negative errno on error.
+ */
+static ssize_t sht15_show_status(struct device *dev,
+                                 struct device_attribute *attr,
+                                 char *buf)
+{
+        int ret;
+        struct sht15_data *data = dev_get_drvdata(dev);
+        u8 bit = to_sensor_dev_attr(attr)->index;
+
+        ret = sht15_update_status(data);
+
+        return ret ? ret : sprintf(buf, "%d\n", !!(data->val_status & bit));
+}
+
+/**
+ * sht15_store_heater() - change heater state via sysfs
+ * @dev:        device.
+ * @attr:       device attribute.
+ * @buf:        sysfs buffer to read the new heater state from.
+ * @count:      length of the data.
+ *
+ * Will be called on read access to heater_enable sysfs attribute.
+ * Returns number of bytes actually decoded, negative errno on error.
+ */
+static ssize_t sht15_store_heater(struct device *dev,
+                                  struct device_attribute *attr,
+                                  const char *buf, size_t count)
+{
+        int ret;
+        struct sht15_data *data = dev_get_drvdata(dev);
+        long value;
+        u8 status;
+
+        if (strict_strtol(buf, 10, &value))
+                return -EINVAL;
+
+        mutex_lock(&data->read_lock);
+        status = data->val_status & 0x07;
+        if (!!value)
+                status |= SHT15_STATUS_HEATER;
+        else
+                status &= ~SHT15_STATUS_HEATER;
+
+        ret = sht15_send_status(data, status);
+        mutex_unlock(&data->read_lock);
+
+        return ret ? ret : count;
+}
+
+/**
  * sht15_show_temp() - show temperature measurement value in sysfs
  * @dev:        device.
  * @attr:       device attribute.
@@ -407,7 +587,6 @@ static ssize_t sht15_show_humidity(struct device *dev,
         ret = sht15_update_measurements(data);
 
         return ret ? ret : sprintf(buf, "%d\n", sht15_calc_humid(data));
-
 }
 
 static ssize_t show_name(struct device *dev,
@@ -422,10 +601,19 @@ static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
                           sht15_show_temp, NULL, 0);
 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
                           sht15_show_humidity, NULL, 0);
+static SENSOR_DEVICE_ATTR(temp1_fault, S_IRUGO, sht15_show_status, NULL,
+                          SHT15_STATUS_LOW_BATTERY);
+static SENSOR_DEVICE_ATTR(humidity1_fault, S_IRUGO, sht15_show_status, NULL,
+                          SHT15_STATUS_LOW_BATTERY);
+static SENSOR_DEVICE_ATTR(heater_enable, S_IRUGO | S_IWUSR, sht15_show_status,
+                          sht15_store_heater, SHT15_STATUS_HEATER);
 static DEVICE_ATTR(name, S_IRUGO, show_name, NULL);
 static struct attribute *sht15_attrs[] = {
         &sensor_dev_attr_temp1_input.dev_attr.attr,
         &sensor_dev_attr_humidity1_input.dev_attr.attr,
+        &sensor_dev_attr_temp1_fault.dev_attr.attr,
+        &sensor_dev_attr_humidity1_fault.dev_attr.attr,
+        &sensor_dev_attr_heater_enable.dev_attr.attr,
         &dev_attr_name.attr,
         NULL,
 };
@@ -466,25 +654,8 @@ static void sht15_ack(struct sht15_data *data)
         gpio_direction_input(data->pdata->gpio_data);
 }
 
-/**
- * sht15_end_transmission() - notify device of end of transmission
- * @data:       device state
- *
- * This is basically a NAK. (single clock pulse, data high)
- */
-static void sht15_end_transmission(struct sht15_data *data)
-{
-        gpio_direction_output(data->pdata->gpio_data, 1);
-        ndelay(SHT15_TSU);
-        gpio_set_value(data->pdata->gpio_sck, 1);
-        ndelay(SHT15_TSCKH);
-        gpio_set_value(data->pdata->gpio_sck, 0);
-        ndelay(SHT15_TSCKL);
-}
-
 static void sht15_bh_read_data(struct work_struct *work_s)
 {
-        int i;
         uint16_t val = 0;
         struct sht15_data *data
                 = container_of(work_s, struct sht15_data,
@@ -505,16 +676,10 @@ static void sht15_bh_read_data(struct work_struct *work_s)
         }
 
         /* Read the data back from the device */
-        for (i = 0; i < 16; ++i) {
-                val <<= 1;
-                gpio_set_value(data->pdata->gpio_sck, 1);
-                ndelay(SHT15_TSCKH);
-                val |= !!gpio_get_value(data->pdata->gpio_data);
-                gpio_set_value(data->pdata->gpio_sck, 0);
-                ndelay(SHT15_TSCKL);
-                if (i == 7)
-                        sht15_ack(data);
-        }
+        val = sht15_read_byte(data);
+        val <<= 8;
+        sht15_ack(data);
+        val |= sht15_read_byte(data);
 
         /* Tell the device we are done */
         sht15_end_transmission(data);
@@ -568,6 +733,7 @@ static int __devinit sht15_probe(struct platform_device *pdev)
 {
         int ret = 0;
         struct sht15_data *data = kzalloc(sizeof(*data), GFP_KERNEL);
+        u8 status = 0;
 
         if (!data) {
                 ret = -ENOMEM;
@@ -588,6 +754,10 @@ static int __devinit sht15_probe(struct platform_device *pdev)
         }
         data->pdata = pdev->dev.platform_data;
         data->supply_uV = data->pdata->supply_mv * 1000;
+        if (data->pdata->no_otp_reload)
+                status |= SHT15_STATUS_NO_OTP_RELOAD;
+        if (data->pdata->low_resolution)
+                status |= SHT15_STATUS_LOW_RESOLUTION;
 
         /*
          * If a regulator is available,
@@ -646,6 +816,13 @@ static int __devinit sht15_probe(struct platform_device *pdev)
         if (ret)
                 goto err_release_irq;
 
+        /* write status with platform data options */
+        if (status) {
+                ret = sht15_send_status(data, status);
+                if (ret)
+                        goto err_release_irq;
+        }
+
         ret = sysfs_create_group(&pdev->dev.kobj, &sht15_attr_group);
         if (ret) {
                 dev_err(&pdev->dev, "sysfs create failed\n");
@@ -689,6 +866,10 @@ static int __devexit sht15_remove(struct platform_device *pdev)
          * prevent new ones beginning
          */
         mutex_lock(&data->read_lock);
+        if (sht15_soft_reset(data)) {
+                mutex_unlock(&data->read_lock);
+                return -EFAULT;
+        }
         hwmon_device_unregister(data->hwmon_dev);
         sysfs_remove_group(&pdev->dev.kobj, &sht15_attr_group);
         if (!IS_ERR(data->reg)) {
diff --git a/include/linux/sht15.h b/include/linux/sht15.h
index 1e302146bdc8..d836ca617323 100644
--- a/include/linux/sht15.h
+++ b/include/linux/sht15.h
@@ -19,10 +19,14 @@
  * @gpio_sck:           no. of gpio to which the data clock is connected.
  * @supply_mv:          supply voltage in mv. Overridden by regulator if
  *                      available.
+ * @no_otp_reload:      flag to indicate no reload from OTP.
+ * @low_resolution:     flag to indicate the temp/humidity resolution to use.
  */
 struct sht15_platform_data {
         int gpio_data;
         int gpio_sck;
         int supply_mv;
+        bool no_otp_reload;
+        bool low_resolution;
 };