drivers: sensor: ds18b20: indicate error for missing response

When multiple devices are on the bus, and no slave matches
the sent rom, the master receives only ones.
This should be handled explicitly and the error reporting
should not rely on the crc mismatch of the scratchpad.

Note: Make sure that the sensor configuration is loaded to the
eeprom (copy scratchpad), otherwise the resolution will not match
the expectations in case a node looses power and recovers.
As in that case the configuration will not be applied again.
Also the sensor may still report the power on reset value
of +85°C just after the sensor powered up.

Signed-off-by: Thomas Stranger <[email protected]>

Author: str4t0m

drivers/sensor/maxim/ds18b20/ds18b20.c

@@ -15,6 +15,8 @@
  * Parasite power configuration is not supported by the driver.
  */
 
+#include <stdbool.h>
+
 #include <zephyr/device.h>
 #include <zephyr/devicetree.h>
 #include <zephyr/drivers/sensor.h>
@@ -96,6 +98,17 @@ static inline void ds18b20_temperature_from_raw(const struct device *dev,
 	}
 }
 
+static inline bool slave_responded(uint8_t *rx_buf, size_t len)
+{
+	uint8_t cmp_byte = 0xff;
+
+	for (int i = 0; i < len; i++) {
+		cmp_byte &= rx_buf[i];
+	}
+
+	return (cmp_byte == 0xff) ? false : true;
+}
+
 /*
  * Write scratch pad, read back, then copy to eeprom
  */
@@ -148,6 +161,11 @@ static int ds18b20_read_scratchpad(const struct device *dev,
 		return ret;
 	}
 
+	if (!slave_responded((uint8_t *)scratchpad, sizeof(*scratchpad))) {
+		LOG_WRN("Slave not reachable");
+		return -ENODEV;
+	}
+
 	crc = w1_crc8((uint8_t *)scratchpad, sizeof(*scratchpad) - 1);
 	if (crc != scratchpad->crc) {
 		LOG_WRN("CRC does not match");