[PATCH v2] 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 set to -1.

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>
---
Changes in v2:
- disable trickle charger if device tree property trickle-resistor-ohms
  is set to -1.
---
 drivers/rtc/rtc-rv3028.c | 45 +++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 12 deletions(-)

diff --git a/drivers/rtc/rtc-rv3028.c b/drivers/rtc/rtc-rv3028.c
index ec5d7a614e2d..da2ae81fe7c8 100644
--- a/drivers/rtc/rtc-rv3028.c
+++ b/drivers/rtc/rtc-rv3028.c
@@ -859,7 +859,8 @@ static int rv3028_probe(struct i2c_client *client)
 {
 	struct rv3028_data *rv3028;
 	int ret, status;
-	u32 ohms;
+	s32 ohms;
+	int val_old, val;
 	struct nvmem_config nvmem_cfg = {
 		.name = "rv3028_nvram",
 		.word_size = 1,
@@ -937,22 +938,42 @@ 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;
+	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);
 
-		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
-			if (ohms == rv3028_trickle_resistors[i])
-				break;
+	/* setup trickle charger */
+	if (!of_property_read_s32(client->dev.of_node, "trickle-resistor-ohms",
+				  &ohms)) {
+		/* disable trickle charger if trickle-resistor-ohms = <(-1)>; */
+		if (ohms == -1) {
+			val = val_old & ~RV3028_BACKUP_TCE;
+		} else {
+			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");
+				/* don't update the trickle charger regs */
+				val = val_old;
+			}
+		}
 
-		if (i < ARRAY_SIZE(rv3028_trickle_resistors)) {
+		/* 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, RV3028_BACKUP_TCE | i);
+						RV3028_BACKUP_TCR_MASK, val);
 			if (ret)
 				return ret;
-		} else {
-			dev_warn(&client->dev, "invalid trickle resistor value\n");
 		}
 	}
 
-- 
2.25.1