drivers: rtc: rtc_ds1307: Fix corruption of SECONDS register

We read/modify/write the CH/SECONDS register at initialisation to clear
only the Clock Halt bit and only if it is set.

The previous implementation zeroes the entire register unconditionally at
initialisation, which wipes the SECONDS fields.

Fixes #77354.

Signed-off-by: Andrew Feldhaus ([email protected])

drivers/rtc/rtc_ds1307.c

@@ -136,13 +136,23 @@ static int ds1307_init(const struct device *dev)
 	/* Disable squarewave output */
 	err = i2c_reg_write_byte_dt(&config->i2c_bus, DS1307_REG_CTRL, 0x00);
 	if (err < 0) {
-		LOG_ERR("Error: SQW:%d\n", err);
+		LOG_ERR("Error: SQW: %d\n", err);
 	}
 
-	/* Make clock halt = 0 */
-	err = i2c_reg_write_byte_dt(&config->i2c_bus, DS1307_REG_SECONDS, 0x00);
+	/* Ensure Clock Halt = 0 */
+	uint8_t reg = 0;
+
+	err = i2c_reg_read_byte_dt(&config->i2c_bus, DS1307_REG_SECONDS, &reg);
 	if (err < 0) {
-		LOG_ERR("Error: Set clock halt bit:%d\n", err);
+		LOG_ERR("Error: Read SECONDS/Clock Halt register: %d\n", err);
+	}
+	if (reg & ~SECONDS_BITS) {
+		/* Clock Halt bit is set */
+		err = i2c_reg_write_byte_dt(&config->i2c_bus, DS1307_REG_SECONDS,
+					    reg & SECONDS_BITS);
+		if (err < 0) {
+			LOG_ERR("Error: Clear Clock Halt bit: %d\n", err);
+		}
 	}
 
 	return 0;