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>

diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
index ac15298a655836334d816129f42adb0ce6fb85ce..3494f7261ebf5ed93c3ee492b9aa564b82867d72 100644 (file)
--- a/drivers/hwmon/ltc2945.c
+++ b/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);
 }