[PATCH 2/2] hwmon: ltc2945: Allow setting shunt resistor

["Cormier, Jonathan" <jcormier@criticallink.com>]

From: John Pruitt <jpruitt@criticallink.com>

Added the ability to specify the value of the shunt resistor in the
device tree instead of assuming it is 1 milliOhm. The value in the
device tree has the name shunt-resistor-micro-ohms and the
default value is 1000 micro-ohms in order to preserve the
current behavior.

Signed-off-by: "Cormier, Jonathan" <jcormier@criticallink.com>
Signed-off-by: John Pruitt <jpruitt@criticallink.com>
---
 drivers/hwmon/ltc2945.c | 86 +++++++++++++++++++++++++++++++----------
 1 file changed, 65 insertions(+), 21 deletions(-)

diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
index 9adebb59f604..4e8b92e53133 100644
--- a/drivers/hwmon/ltc2945.c
+++ b/drivers/hwmon/ltc2945.c
@@ -58,6 +58,11 @@
 #define CONTROL_MULT_SELECT	(1 << 0)
 #define CONTROL_TEST_MODE	(1 << 4)
 
+struct ltc2945_data {
+	struct regmap *regmap;
+	u32 shunt_resistor; // number of microohms
+};
+
 static inline bool is_power_reg(u8 reg)
 {
 	return reg < LTC2945_SENSE_H;
@@ -66,7 +71,9 @@ static inline bool is_power_reg(u8 reg)
 /* Return the value from the given register in uW, mV, or mA */
 static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 {
-	struct regmap *regmap = dev_get_drvdata(dev);
+	struct ltc2945_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
+	u32 shunt_resistor = data->shunt_resistor;
 	unsigned int control;
 	u8 buf[3];
 	long long val;
@@ -93,8 +100,11 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 	case LTC2945_MIN_POWER_THRES_H:
 		/*
 		 * Convert to uW by assuming current is measured with
-		 * an 1mOhm sense resistor, similar to current
-		 * measurements.
+		 * a 1000 microOhm sense resistor (aka shunt resistor)
+		 * or what is specified in DT, similar to current
+		 * measurements. The shunt_resistor value is in
+		 * microOhms.
+		 *
 		 * Control register bit 0 selects if voltage at SENSE+/VDD
 		 * or voltage at ADIN is used to measure power.
 		 */
@@ -108,6 +118,8 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 			/* 0.5 mV * 25 uV = 0.0125 uV resolution. */
 			val = (val * 25LL) >> 1;
 		}
+		val *= 1000;
+		val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
 		break;
 	case LTC2945_VIN_H:
 	case LTC2945_MAX_VIN_H:
@@ -132,12 +144,15 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 	case LTC2945_MIN_SENSE_THRES_H:
 		/*
 		 * 25 uV resolution. Convert to current as measured with
-		 * an 1 mOhm sense resistor, in mA. If a different sense
-		 * resistor is installed, calculate the actual current by
-		 * dividing the reported current by the sense resistor value
-		 * in mOhm.
+		 * an 1000 microOhm sense (or shunt) resistor, in mA.
+		 * If a different shunt resistor is installed, calculate
+		 * the actual current by dividing the reported current
+		 * by the shunt resistor value in microOhms. The actual
+		 * The actual shunt resistor value can be specified
+		 * in the device tree.
 		 */
-		val *= 25;
+		val *= 25 * 1000;
+		val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
 		break;
 	default:
 		return -EINVAL;
@@ -148,7 +163,9 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 			      unsigned long val)
 {
-	struct regmap *regmap = dev_get_drvdata(dev);
+	struct ltc2945_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
+	u32 shunt_resistor = data->shunt_resistor;
 	unsigned int control;
 	int ret;
 
@@ -160,8 +177,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 	case LTC2945_MIN_POWER_THRES_H:
 		/*
 		 * Convert to register value by assuming current is measured
-		 * with an 1mOhm sense resistor, similar to current
+		 * with a 1000 microOhm sense resistor, (aka shunt resistor)
+		 * or what is specified in DT, similar to current
 		 * measurements.
+		 *
 		 * Control register bit 0 selects if voltage at SENSE+/VDD
 		 * or voltage at ADIN is used to measure power, which in turn
 		 * determines register calculations.
@@ -171,14 +190,16 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 			return ret;
 		if (control & CONTROL_MULT_SELECT) {
 			/* 25 mV * 25 uV = 0.625 uV resolution. */
-			val = DIV_ROUND_CLOSEST(val, 625);
+			val *= shunt_resistor;
+			val = DIV_ROUND_CLOSEST(val, 625 * 1000);
 		} else {
 			/*
 			 * 0.5 mV * 25 uV = 0.0125 uV resolution.
 			 * Divide first to avoid overflow;
 			 * accept loss of accuracy.
 			 */
-			val = DIV_ROUND_CLOSEST(val, 25) * 2;
+			val *= shunt_resistor;
+			val = DIV_ROUND_CLOSEST(val, 25 * 1000) * 2;
 		}
 		break;
 	case LTC2945_VIN_H:
@@ -204,12 +225,14 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 	case LTC2945_MIN_SENSE_THRES_H:
 		/*
 		 * 25 uV resolution. Convert to current as measured with
-		 * an 1 mOhm sense resistor, in mA. If a different sense
-		 * resistor is installed, calculate the actual current by
-		 * dividing the reported current by the sense resistor value
-		 * in mOhm.
+		 * a 1000 microOhm sense (or shunt) resistor, in mA. If
+		 * a different shunt resistor is installed, calculate
+		 * the actual current by dividing the reported current
+		 * by the sense resistor value in microOhms. The actual
+		 * shunt resistor value can be specified in the device tree.
 		 */
-		val = DIV_ROUND_CLOSEST(val, 25);
+		val *= shunt_resistor;
+		val = DIV_ROUND_CLOSEST(val, 25 * 1000);
 		break;
 	default:
 		return -EINVAL;
@@ -234,7 +257,8 @@ static ssize_t ltc2945_value_store(struct device *dev,
 				   const char *buf, size_t count)
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
-	struct regmap *regmap = dev_get_drvdata(dev);
+	struct ltc2945_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
 	u8 reg = attr->index;
 	unsigned long val;
 	u8 regbuf[3];
@@ -269,7 +293,8 @@ static ssize_t ltc2945_history_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
-	struct regmap *regmap = dev_get_drvdata(dev);
+	struct ltc2945_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
 	u8 reg = attr->index;
 	int num_regs = is_power_reg(reg) ? 3 : 2;
 	u8 buf_min[3] = { 0xff, 0xff, 0xff };
@@ -321,7 +346,8 @@ static ssize_t ltc2945_bool_show(struct device *dev,
 				 struct device_attribute *da, char *buf)
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
-	struct regmap *regmap = dev_get_drvdata(dev);
+	struct ltc2945_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
 	unsigned int fault;
 	int ret;
 
@@ -450,6 +476,14 @@ static int ltc2945_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct device *hwmon_dev;
 	struct regmap *regmap;
+	u32 shunt_resistor;
+
+	struct ltc2945_data *data;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	dev_set_drvdata(dev, data);
 
 	regmap = devm_regmap_init_i2c(client, &ltc2945_regmap_config);
 	if (IS_ERR(regmap)) {
@@ -457,11 +491,21 @@ static int ltc2945_probe(struct i2c_client *client)
 		return PTR_ERR(regmap);
 	}
 
+	data->regmap = regmap;
+	if (of_property_read_u32(client->dev.of_node,
+				 "shunt-resistor-micro-ohms", &shunt_resistor))
+		shunt_resistor = 1000; /* 1000 micro-Ohm if not set via DT */
+
+	if (shunt_resistor == 0)
+		return -EINVAL;
+
+	data->shunt_resistor = shunt_resistor;
+
 	/* Clear faults */
 	regmap_write(regmap, LTC2945_FAULT, 0x00);
 
 	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
-							   regmap,
+							   data,
 							   ltc2945_groups);
 	return PTR_ERR_OR_ZERO(hwmon_dev);
 }
-- 
2.25.1