drivers: fixed div by zero when reading max17048

Avoid divsion by zero when current rate is zero

Signed-off-by: Alvaro Garcia <[email protected]>

Author: maxpowel

drivers/fuel_gauge/max17048/emul_max17048.c

@@ -21,6 +21,13 @@ LOG_MODULE_REGISTER(maxim_max17048);
 
 #include "max17048.h"
 
+static int crate_value = 0x4000;
+
+void emul_max17048_set_crate_status(int value)
+{
+	crate_value = value;
+}
+
 /** Static configuration for the emulator */
 struct max17048_emul_cfg {
 	/** I2C address of emulator */
@@ -41,7 +48,7 @@ static int emul_max17048_reg_read(const struct emul *target, int reg, int *val)
 	*val = 0x1000;
 		break;
 	case REGISTER_CRATE:
-	*val = 0x4000;
+	*val = crate_value;
 	break;
 	case REGISTER_SOC:
 	*val = 0x3525;

drivers/fuel_gauge/max17048/max17048.c

@@ -234,41 +234,53 @@ static int max17048_get_props(const struct device *dev, struct fuel_gauge_get_pr
 		return rc;
 	}
 
-	/**
-	 * May take some time until the chip detects the change between discharging to charging
-	 * (and vice versa) especially if your device consumes little power
-	 */
-	data->charging = crate > 0;
-
-
-	/**
-	 * In the following code, we multiply by 1000 the charge to increase the precision. If we
-	 * just truncate the division without this multiplier, the precision lost is very
-	 * significant when converting it into minutes (the value given is in hours)
-	 *
-	 * The value coming from crate is already 1000 times higher (check the function
-	 * max17048_crate to
-	 * see the reason) so the multiplier for the charge
-	 * will be 1000000
-	 */
-	if (data->charging) {
-		uint8_t percentage_pending = 100 - data->charge;
-		uint32_t hours_pending = percentage_pending * 1000000 / crate;
-
-		data->time_to_empty = 0;
-		data->time_to_full = hours_pending * 60 / 1000;
+	if (crate != 0) {
+
+		/**
+		 * May take some time until the chip detects the change between discharging to
+		 * charging (and vice versa) especially if your device consumes little power
+		 */
+		data->charging = crate > 0;
+
+
+		/**
+		 * In the following code, we multiply by 1000 the charge to increase the
+		 * precision. If we just truncate the division without this multiplier,
+		 * the precision lost is very significant when converting it into minutes
+		 * (the value given is in hours)
+		 *
+		 * The value coming from crate is already 1000 times higher (check the
+		 * function max17048_crate to see the reason) so the multiplier for the
+		 * charge will be 1000000
+		 */
+		if (data->charging) {
+			uint8_t percentage_pending = 100 - data->charge;
+			uint32_t hours_pending = percentage_pending * 1000000 / crate;
+
+			data->time_to_empty = 0;
+			data->time_to_full = hours_pending * 60 / 1000;
+		} else {
+			/* Discharging */
+			uint32_t hours_pending = data->charge * 1000000 / -crate;
+
+			data->time_to_empty = hours_pending * 60 / 1000;
+			data->time_to_full = 0;
+		}
+
+		for (int i = 0; i < len; i++) {
+			int ret = max17048_get_prop(dev, props + i);
+
+			err_count += ret ? 1 : 0;
+		}
 	} else {
-		/* Discharging */
-		uint32_t hours_pending = data->charge * 1000000 / -crate;
-
-		data->time_to_empty = hours_pending * 60 / 1000;
+		/**
+		 * This case is to avoid a division by 0 when the charge rate is the same
+		 * than consumption rate. It could also happen when the sensor is still
+		 * calibrating the battery
+		 */
+		data->charging = false;
 		data->time_to_full = 0;
-	}
-
-	for (int i = 0; i < len; i++) {
-		int ret = max17048_get_prop(dev, props + i);
-
-		err_count += ret ? 1 : 0;
+		data->time_to_empty = 0;
 	}
 
 	err_count = (err_count == len) ? -1 : err_count;

tests/drivers/fuel_gauge/max17048/src/test_max17048.c

@@ -18,12 +18,13 @@ struct max17048_fixture {
 	const struct fuel_gauge_driver_api *api;
 };
 
+void emul_max17048_set_crate_status(int value);
+
 static void *max17048_setup(void)
 {
 	static ZTEST_DMEM struct max17048_fixture fixture;
 
 	fixture.dev = DEVICE_DT_GET_ANY(maxim_max17048);
-
 	k_object_access_all_grant(fixture.dev);
 
 	zassert_true(device_is_ready(fixture.dev), "Fuel Gauge not found");
@@ -110,5 +111,42 @@ ZTEST_USER_F(max17048, test_get_props__returns_ok)
 	zassert_ok(ret);
 }
 
+ZTEST_USER_F(max17048, test_current_rate_zero)
+{
+	/* Test when crate is 0, which is a special case */
+
+	struct fuel_gauge_get_property props[] = {
+		{
+			.property_type = FUEL_GAUGE_RUNTIME_TO_EMPTY,
+		},
+		{
+			.property_type = FUEL_GAUGE_RUNTIME_TO_FULL,
+		}
+	};
+
+	/** Null value, not charging either discharging. If not handled correctly,
+	 * it will cause a division by zero
+	 */
+	emul_max17048_set_crate_status(0);
+	int ret = fuel_gauge_get_prop(fixture->dev, props, ARRAY_SIZE(props));
+
+	for (int i = 0; i < ARRAY_SIZE(props); i++) {
+		zassert_ok(props[i].status, "Property %d getting %d has a bad status.", i,
+			   props[i].property_type);
+	}
+	zassert_equal(props[0].value.runtime_to_empty, 0,
+		"Runtime to empty is %d but it should be 0.",
+		props[0].value.runtime_to_full
+	);
+	zassert_equal(props[1].value.runtime_to_full, 0,
+		"Runtime to full is %d but it should be 0.",
+		props[1].value.runtime_to_full
+	);
+
+	zassert_ok(ret);
+	/* Return value to the original state */
+	emul_max17048_set_crate_status(0x4000);
+}
+
 
 ZTEST_SUITE(max17048, NULL, max17048_setup, NULL, NULL, NULL);