regulator: max8973: add support to configure ETR based on rail load

Add support to configure Enhanced Transient Response Enable (ETR)
and Sensitivity Selection based on maximum current i.e. expected
load on that rail.

Maxim recommended as:
- Enable ETR with high sensitivity (75mV/us) for 0 to 9A expected loads,
- Enable ETR with low sensitivity (150mV/us) for 9A to 12A expected loads.
- Disable ETR for expected load > 12A.

These recommendation will be configured for MAX77621 when maximum load
is provided through regulator constraint for maximum current from platform.

Signed-off-by: Laxman Dewangan <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/max8973-regulator.c

···
 #define MAX8973_DISCH_ENBABLE				BIT(5)
 #define MAX8973_FT_ENABLE				BIT(4)
 
+#define MAX8973_CKKADV_TRIP_MASK			0xC
 #define MAX8973_CKKADV_TRIP_DISABLE			0xC
 #define MAX8973_CKKADV_TRIP_75mV_PER_US			0x0
 #define MAX8973_CKKADV_TRIP_150mV_PER_US		0x4
···
 		dev_err(max->dev, "register %d update failed, %d",
 				MAX8973_CONTROL1, ret);
 	return ret;
+}
+
+static int max8973_set_current_limit(struct regulator_dev *rdev,
+		int min_ua, int max_ua)
+{
+	struct max8973_chip *max = rdev_get_drvdata(rdev);
+	unsigned int val;
+	int ret;
+
+	if (max_ua <= 9000000)
+		val = MAX8973_CKKADV_TRIP_75mV_PER_US;
+	else if (max_ua <= 12000000)
+		val = MAX8973_CKKADV_TRIP_150mV_PER_US;
+	else
+		val = MAX8973_CKKADV_TRIP_DISABLE;
+
+	ret = regmap_update_bits(max->regmap, MAX8973_CONTROL2,
+			MAX8973_CKKADV_TRIP_MASK, val);
+	if (ret < 0) {
+		dev_err(max->dev, "register %d update failed: %d\n",
+				MAX8973_CONTROL2, ret);
+		return ret;
+	}
+	return 0;
+}
+
+static int max8973_get_current_limit(struct regulator_dev *rdev)
+{
+	struct max8973_chip *max = rdev_get_drvdata(rdev);
+	unsigned int control2;
+	int ret;
+
+	ret = regmap_read(max->regmap, MAX8973_CONTROL2, &control2);
+	if (ret < 0) {
+		dev_err(max->dev, "register %d read failed: %d\n",
+				MAX8973_CONTROL2, ret);
+		return ret;
+	}
+	switch (control2 & MAX8973_CKKADV_TRIP_MASK) {
+	case MAX8973_CKKADV_TRIP_DISABLE:
+		return 15000000;
+	case MAX8973_CKKADV_TRIP_150mV_PER_US:
+		return 12000000;
+	case MAX8973_CKKADV_TRIP_75mV_PER_US:
+		return 9000000;
+	default:
+		break;
+	}
+	return 9000000;
 }
 
 static const struct regulator_ops max8973_dcdc_ops = {
···
 		max->ops.enable = regulator_enable_regmap;
 		max->ops.disable = regulator_disable_regmap;
 		max->ops.is_enabled = regulator_is_enabled_regmap;
+		max->ops.set_current_limit = max8973_set_current_limit;
+		max->ops.get_current_limit = max8973_get_current_limit;
 		break;
 	default:
 		break;