rtc: rv3028: Add support for "aux-voltage-chargeable" property

Property "trickle-resistor-ohms" allows us to set trickle charger
resistor. However there is no possibility to disable it afterwards.

Add support for "aux-voltage-chargeable" property which can be used to
enable/disable the trickle charger circuit explicitly. The default
behavior of the code is kept as it is!

Additionally, lets make sure we only update internal EEPROM in case of a
change. This prevents wear due to excessive EEPROM writes on each probe.
Signed-off-by: Andrej Picej <andrej.picej@norik.com>
Link: https://lore.kernel.org/r/20230623081533.76334-1-andrej.picej@norik.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rv3028.c

@@ -855,11 +855,68 @@ static const struct regmap_config regmap_config = {
         .max_register = 0x37,
 };
 
+static u8 rv3028_set_trickle_charger(struct rv3028_data *rv3028,
+				     struct i2c_client *client)
+{
+	int ret, val_old, val;
+	u32 ohms, chargeable;
+
+	ret = regmap_read(rv3028->regmap, RV3028_BACKUP, &val_old);
+	if (ret < 0)
+		return ret;
+
+	/* mask out only trickle charger bits */
+	val_old = val_old & (RV3028_BACKUP_TCE | RV3028_BACKUP_TCR_MASK);
+	val = val_old;
+
+	/* setup trickle charger */
+	if (!device_property_read_u32(&client->dev, "trickle-resistor-ohms",
+				      &ohms)) {
+		int i;
+
+		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
+			if (ohms == rv3028_trickle_resistors[i])
+				break;
+
+		if (i < ARRAY_SIZE(rv3028_trickle_resistors)) {
+			/* enable trickle charger and its resistor */
+			val = RV3028_BACKUP_TCE | i;
+		} else {
+			dev_warn(&client->dev, "invalid trickle resistor value\n");
+		}
+	}
+
+	if (!device_property_read_u32(&client->dev, "aux-voltage-chargeable",
+				      &chargeable)) {
+		switch (chargeable) {
+		case 0:
+			val &= ~RV3028_BACKUP_TCE;
+			break;
+		case 1:
+			val |= RV3028_BACKUP_TCE;
+			break;
+		default:
+			dev_warn(&client->dev,
+				 "unsupported aux-voltage-chargeable value\n");
+			break;
+		}
+	}
+
+	/* only update EEPROM if changes are necessary */
+	if (val_old != val) {
+		ret = rv3028_update_cfg(rv3028, RV3028_BACKUP, RV3028_BACKUP_TCE |
+						RV3028_BACKUP_TCR_MASK, val);
+		if (ret)
+			return ret;
+	}
+
+	return ret;
+}
+
 static int rv3028_probe(struct i2c_client *client)
 {
 	struct rv3028_data *rv3028;
 	int ret, status;
-	u32 ohms;
 	struct nvmem_config nvmem_cfg = {
 		.name = "rv3028_nvram",
 		.word_size = 1,
@@ -937,24 +994,9 @@ static int rv3028_probe(struct i2c_client *client)
 	if (ret)
 		return ret;
 
-	/* setup trickle charger */
-	if (!device_property_read_u32(&client->dev, "trickle-resistor-ohms",
-				      &ohms)) {
-		int i;
-
-		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
-			if (ohms == rv3028_trickle_resistors[i])
-				break;
-
-		if (i < ARRAY_SIZE(rv3028_trickle_resistors)) {
-			ret = rv3028_update_cfg(rv3028, RV3028_BACKUP, RV3028_BACKUP_TCE |
-						 RV3028_BACKUP_TCR_MASK, RV3028_BACKUP_TCE | i);
-			if (ret)
-				return ret;
-		} else {
-			dev_warn(&client->dev, "invalid trickle resistor value\n");
-		}
-	}
+	ret = rv3028_set_trickle_charger(rv3028, client);
+	if (ret)
+		return ret;
 
 	ret = rtc_add_group(rv3028->rtc, &rv3028_attr_group);
 	if (ret)