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

From: Cormier, Jonathan
Date: Wed Dec 14 2022 - 17:07:56 EST

From: John Pruitt <jpruitt@xxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxx>
Signed-off-by: John Pruitt <jpruitt@xxxxxxxxxxxxxxxx>
---
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