[PATCH] rtc: rv3028: Improve trickle charger logic

[Andrej Picej <andrej.picej@norik.com>]

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

From now on, disable trickle charger circuit in case device-tree
property "trickle-resistor-ohms" is not present. RV3029 RTC driver uses
the same trickle charger disable logic.

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>
---
 drivers/rtc/rtc-rv3028.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/rtc/rtc-rv3028.c b/drivers/rtc/rtc-rv3028.c
index ec5d7a614e2d..190507bf97d0 100644
--- a/drivers/rtc/rtc-rv3028.c
+++ b/drivers/rtc/rtc-rv3028.c
@@ -860,6 +860,7 @@ static int rv3028_probe(struct i2c_client *client)
 	struct rv3028_data *rv3028;
 	int ret, status;
 	u32 ohms;
+	int val_old, val;
 	struct nvmem_config nvmem_cfg = {
 		.name = "rv3028_nvram",
 		.word_size = 1,
@@ -937,9 +938,18 @@ static int rv3028_probe(struct i2c_client *client)
 	if (ret)
 		return ret;
 
+	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);
+
 	/* setup trickle charger */
-	if (!device_property_read_u32(&client->dev, "trickle-resistor-ohms",
-				      &ohms)) {
+	if (device_property_read_u32(&client->dev, "trickle-resistor-ohms", &ohms)) {
+		/* disable the trickle charger */
+		val = 0;
+	} else {
 		int i;
 
 		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
@@ -947,15 +957,21 @@ static int rv3028_probe(struct i2c_client *client)
 				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;
+			/* enable the trickle charger and setup its resistor accordingly */
+			val = RV3028_BACKUP_TCE | i;
 		} else {
 			dev_warn(&client->dev, "invalid trickle resistor value\n");
 		}
 	}
 
+	/* 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;
+	}
+
 	ret = rtc_add_group(rv3028->rtc, &rv3028_attr_group);
 	if (ret)
 		return ret;
-- 
2.25.1