drivers: sensor: tmp1075: add support for fractional threshold values

Previously, the TMP1075 driver only used the integer part (val1) of the
sensor_value when setting TLOW and THIGH thresholds. This limited the
precision of temperature threshold configuration and could be insufficient
in applications requiring fine-grained control.

This patch adds proper handling for the fractional part (val2) by encoding
it into bits [7:4] of the 12-bit temperature register according to the
TMP1075 datasheet. The decoding logic in get_threshold_attribute() is also
updated to recover the fractional value accurately.

Signed-off-by: Hank Wang <wanghanchi2000@gmail.com>

Author: WangHanChi

drivers/sensor/ti/tmp1075/tmp1075.c

@@ -67,12 +67,22 @@ static int tmp1075_attr_set(const struct device *dev, enum sensor_channel chan,
 
 	switch (attr) {
 #if CONFIG_TMP1075_ALERT_INTERRUPTS
+		int integer, frac;
+
 	case SENSOR_ATTR_LOWER_THRESH:
-		return set_threshold_attribute(dev, TMP1075_REG_TLOW, val->val1 << 8,
+		/* Extract integer and fractional parts from TMP1075 12-bit register value */
+		integer = (val->val1 << TMP1075_DATA_INTE_SHIFT) & TMP1075_DATA_INTE_MASK;
+		frac = ((val->val2 / TMP1075_TEMP_SCALE) << TMP1075_DATA_FRAC_SHIFT) &
+		       TMP1075_DATA_FRAC_MASK;
+		return set_threshold_attribute(dev, TMP1075_REG_TLOW, integer | frac,
 					       "SENSOR_ATTR_LOWER_THRESH");
 
 	case SENSOR_ATTR_UPPER_THRESH:
-		return set_threshold_attribute(dev, TMP1075_REG_THIGH, val->val1 << 8,
+		/* Extract integer and fractional parts from TMP1075 12-bit register value */
+		integer = (val->val1 << TMP1075_DATA_INTE_SHIFT) & TMP1075_DATA_INTE_MASK;
+		frac = ((val->val2 / TMP1075_TEMP_SCALE) << TMP1075_DATA_FRAC_SHIFT) &
+		       TMP1075_DATA_FRAC_MASK;
+		return set_threshold_attribute(dev, TMP1075_REG_THIGH, integer | frac,
 					       "SENSOR_ATTR_UPPER_THRESH");
 #endif
 
@@ -91,7 +101,9 @@ static int get_threshold_attribute(const struct device *dev, uint8_t reg, struct
 		LOG_ERR("Failed to get %s attribute!", error_msg);
 		return -EIO;
 	}
-	val->val1 = value >> 8;
+	val->val1 = (value & TMP1075_DATA_INTE_MASK) >> TMP1075_DATA_INTE_SHIFT;
+	val->val2 =
+		((value & TMP1075_DATA_FRAC_MASK) >> TMP1075_DATA_FRAC_SHIFT) * TMP1075_TEMP_SCALE;
 	return 0;
 }
 #endif

drivers/sensor/ti/tmp1075/tmp1075.h

@@ -14,6 +14,10 @@
 
 /* Extended resolution is not supported on TMP1075 */
 #define TMP1075_DATA_NORMAL_SHIFT 4
+#define TMP1075_DATA_FRAC_SHIFT   4
+#define TMP1075_DATA_FRAC_MASK    0x00F0
+#define TMP1075_DATA_INTE_SHIFT   8
+#define TMP1075_DATA_INTE_MASK    0xFF00
 #define uCELSIUS_IN_CELSIUS       1000000
 
 #define TMP1075_REG_TEMPERATURE 0x00