hwmon: (ltc2945) Allow setting shunt resistor

Add 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: Jonathan Cormier <jcormier@criticallink.com>
Signed-off-by: John Pruitt <jpruitt@criticallink.com>
[groeck: Fixed multi-line alignment, squashed last patch of series]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/ltc2945.c

@@ -64,6 +64,16 @@ static const struct of_device_id __maybe_unused ltc2945_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, ltc2945_of_match);
 
+/**
+ * struct ltc2945_data - LTC2945 device data
+ * @regmap: regmap device
+ * @shunt_resistor: shunt resistor value in micro ohms (1000 by default)
+ */
+struct ltc2945_data {
+	struct regmap *regmap;
+	u32 shunt_resistor;
+};
+
 static inline bool is_power_reg(u8 reg)
 {
 	return reg < LTC2945_SENSE_H;
@@ -72,7 +82,9 @@ 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;
@@ -84,10 +96,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 		return ret;
 
 	if (is_power_reg(reg)) {
-		/* power */
+		/* 24-bit power */
 		val = (buf[0] << 16) + (buf[1] << 8) + buf[2];
 	} else {
-		/* current, voltage */
+		/* 12-bit current, voltage */
 		val = (buf[0] << 4) + (buf[1] >> 4);
 	}
 
@@ -98,9 +110,7 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 	case LTC2945_MAX_POWER_THRES_H:
 	case LTC2945_MIN_POWER_THRES_H:
 		/*
-		 * Convert to uW by assuming current is measured with
-		 * an 1mOhm sense resistor, similar to current
-		 * measurements.
+		 * Convert to uW
 		 * Control register bit 0 selects if voltage at SENSE+/VDD
 		 * or voltage at ADIN is used to measure power.
 		 */
@@ -114,6 +124,14 @@ 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;
+		/* Overflow check: Assuming max 24-bit power, val is at most 53 bits right now. */
+		val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
+		/*
+		 * Overflow check: After division, depending on shunt resistor,
+		 * val can still be > 32 bits so returning long long makes sense
+		 */
+
 		break;
 	case LTC2945_VIN_H:
 	case LTC2945_MAX_VIN_H:
@@ -136,14 +154,11 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 	case LTC2945_MIN_SENSE_H:
 	case LTC2945_MAX_SENSE_THRES_H:
 	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.
-		 */
-		val *= 25;
+		/* 25 uV resolution. Convert to mA. */
+		val *= 25 * 1000;
+		/* Overflow check: Assuming max 12-bit sense, val is at most 27 bits right now */
+		val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
+		/* Overflow check: After division, <= 27 bits */
 		break;
 	default:
 		return -EINVAL;
@@ -151,13 +166,18 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
 	return val;
 }
 
-static int ltc2945_val_to_reg(struct device *dev, u8 reg,
-			      unsigned long val)
+static long long ltc2945_val_to_reg(struct device *dev, u8 reg,
+				    unsigned long 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;
 
+	/* Ensure we don't overflow */
+	val = clamp_val(val, 0, U32_MAX);
+
 	switch (reg) {
 	case LTC2945_POWER_H:
 	case LTC2945_MAX_POWER_H:
@@ -165,9 +185,6 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 	case LTC2945_MAX_POWER_THRES_H:
 	case LTC2945_MIN_POWER_THRES_H:
 		/*
-		 * Convert to register value by assuming current is measured
-		 * with an 1mOhm sense resistor, 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.
@@ -177,14 +194,16 @@ 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;
+			/* Overflow check: Assuming 32-bit val and shunt resistor, val <= 64bits */
+			val = DIV_ROUND_CLOSEST_ULL(val, 625 * 1000);
+			/* Overflow check: val is now <= 44 bits */
 		} 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;
+			/* 0.5 mV * 25 uV = 0.0125 uV resolution. */
+			val *= shunt_resistor;
+			/* Overflow check: Assuming 32-bit val and shunt resistor, val <= 64bits */
+			val = DIV_ROUND_CLOSEST_ULL(val, 25 * 1000) * 2;
+			/* Overflow check: val is now <= 51 bits */
 		}
 		break;
 	case LTC2945_VIN_H:
@@ -193,7 +212,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 	case LTC2945_MAX_VIN_THRES_H:
 	case LTC2945_MIN_VIN_THRES_H:
 		/* 25 mV resolution. */
-		val /= 25;
+		val = DIV_ROUND_CLOSEST_ULL(val, 25);
 		break;
 	case LTC2945_ADIN_H:
 	case LTC2945_MAX_ADIN_H:
@@ -208,14 +227,11 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
 	case LTC2945_MIN_SENSE_H:
 	case LTC2945_MAX_SENSE_THRES_H:
 	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.
-		 */
-		val = DIV_ROUND_CLOSEST(val, 25);
+		/* 25 uV resolution. Convert to  mA. */
+		val *= shunt_resistor;
+		/* Overflow check: Assuming 32-bit val and 32-bit shunt resistor, val is 64bits */
+		val = DIV_ROUND_CLOSEST_ULL(val, 25 * 1000);
+		/* Overflow check: val is now <= 50 bits */
 		break;
 	default:
 		return -EINVAL;
@@ -240,15 +256,16 @@ 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;
+	unsigned int val;
 	u8 regbuf[3];
 	int num_regs;
-	int regval;
+	long long regval;
 	int ret;
 
-	ret = kstrtoul(buf, 10, &val);
+	ret = kstrtouint(buf, 10, &val);
 	if (ret)
 		return ret;
 
@@ -277,7 +294,8 @@ 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 };
@@ -329,7 +347,8 @@ 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;
 
@@ -458,6 +477,12 @@ static int ltc2945_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct device *hwmon_dev;
 	struct regmap *regmap;
+	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)) {
@@ -465,11 +490,19 @@ static int ltc2945_probe(struct i2c_client *client)
 		return PTR_ERR(regmap);
 	}
 
+	data->regmap = regmap;
+	if (device_property_read_u32(dev, "shunt-resistor-micro-ohms",
+				     &data->shunt_resistor))
+		data->shunt_resistor = 1000;
+
+	if (data->shunt_resistor == 0)
+		return -EINVAL;
+
 	/* 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);
 }