[PATCH] rtc: ds3232: add temperature support

[Kirill Esipov]

DS3232/DS3234 has the temperature registers with a resolution of
0.25 degree celsius. This enables to get the value through hwmon.

	# cat /sys/class/hwmon/hwmon0/temp1_input
	37250

Signed-off-by: Kirill Esipov <yesipov@xxxxxxxxx>
---
 drivers/rtc/Kconfig      |  9 ++++++
 drivers/rtc/rtc-ds3232.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 8d3b95728326..b4a6a916d4df 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -791,6 +791,15 @@ config RTC_DRV_DS3232
 	  This driver can also be built as a module.  If so, the module
 	  will be called rtc-ds3232.
 
+config RTC_DRV_DS3232_HWMON
+	bool "HWMON support for Dallas/Maxim DS3232/DS3234"
+	depends on RTC_DRV_DS3232 && HWMON
+	depends on !(RTC_DRV_DS3232=y && HWMON=m)
+	default y
+	help
+	  Say Y here if you want to expose temperature sensor data on
+	  rtc-ds3232
+
 config RTC_DRV_PCF2127
 	tristate "NXP PCF2127"
 	depends on RTC_I2C_AND_SPI
diff --git a/drivers/rtc/rtc-ds3232.c b/drivers/rtc/rtc-ds3232.c
index deff431a37c4..f94ff0685942 100644
--- a/drivers/rtc/rtc-ds3232.c
+++ b/drivers/rtc/rtc-ds3232.c
@@ -22,6 +22,8 @@
 #include <linux/bcd.h>
 #include <linux/slab.h>
 #include <linux/regmap.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
 
 #define DS3232_REG_SECONDS      0x00
 #define DS3232_REG_MINUTES      0x01
@@ -275,6 +277,86 @@ static int ds3232_update_alarm(struct device *dev, unsigned int enabled)
 	return ret;
 }
 
+/*----------------------------------------------------------------------*/
+
+#ifdef CONFIG_RTC_DRV_DS3232_HWMON
+
+/*
+ * Temperature sensor support for ds3232/ds3234 devices.
+ */
+
+#define DS3232_REG_TEMPERATURE	0x11
+
+/*
+ * A user-initiated temperature conversion is not started by this function,
+ * so the temperature is updated once every 64 seconds.
+ */
+static int ds3232_hwmon_read_temp(struct device *dev, s32 *mC)
+{
+	struct ds3232 *ds3232 = dev_get_drvdata(dev);
+	u8 temp_buf[2];
+	s16 temp;
+	int ret;
+
+	ret = regmap_bulk_read(ds3232->regmap, DS3232_REG_TEMPERATURE, temp_buf,
+				sizeof(temp_buf));
+
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Temperature is represented as a 10-bit code with a resolution of
+	 * 0.25 degree celsius and encoded in two's complement format.
+	 */
+	temp = (temp_buf[0] << 8) | temp_buf[1];
+	temp >>= 6;
+	*mC = temp * 250;
+
+	return 0;
+}
+
+static ssize_t ds3232_hwmon_show_temp(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	int ret;
+	s32 temp;
+
+	ret = ds3232_hwmon_read_temp(dev, &temp);
+	if (ret < 0)
+		return ret;
+
+	return sprintf(buf, "%d\n", temp);
+}
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, ds3232_hwmon_show_temp,
+			NULL, 0);
+
+static struct attribute *ds3232_hwmon_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(ds3232_hwmon);
+
+static void ds3232_hwmon_register(struct device *dev, const char *name)
+{
+	struct ds3232 *ds3232 = dev_get_drvdata(dev);
+	struct device *hwmon_dev;
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(dev, name, ds3232,
+							   ds3232_hwmon_groups);
+	if (IS_ERR(hwmon_dev)) {
+		dev_warn(dev, "unable to register hwmon device %ld\n",
+			 PTR_ERR(hwmon_dev));
+	}
+}
+
+#else
+
+static void ds3232_hwmon_register(struct ds3232 *ds3232)
+{
+}
+
+#endif
+
 static int ds3232_alarm_irq_enable(struct device *dev, unsigned int enabled)
 {
 	struct ds3232 *ds3232 = dev_get_drvdata(dev);
@@ -366,6 +448,8 @@ static int ds3232_probe(struct device *dev, struct regmap *regmap, int irq,
 	if (ds3232->irq > 0)
 		device_init_wakeup(dev, 1);
 
+	ds3232_hwmon_register(dev, name);
+
 	ds3232->rtc = devm_rtc_device_register(dev, name, &ds3232_rtc_ops,
 						THIS_MODULE);
 	if (IS_ERR(ds3232->rtc))
-- 
2.7.4