On Fri, Nov 06, 2020 at 12:18:25PM +0200, Alexandru Ardelean wrote: > The sense resistor is a parameter of the board. It should be configured in > the driver via a device-tree / ACPI property, so that the proper current > measurements can be done in the driver. > > It shouldn't be necessary that userspace need to know about the value of > the resistor. It makes things a bit harder to make the application code > portable from one board to another. > > This change implements support for the sense resistor to be configured from > DT/ACPI and used in current calculations. >
This will require a matching deevicetree document. > Signed-off-by: Alexandru Ardelean <[email protected]> > --- > drivers/hwmon/ltc2945.c | 48 ++++++++++++++++++----------------------- > 1 file changed, 21 insertions(+), 27 deletions(-) > > diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c > index 75d997d31e01..500401a82c49 100644 > --- a/drivers/hwmon/ltc2945.c > +++ b/drivers/hwmon/ltc2945.c > @@ -61,9 +61,11 @@ > /** > * struct ltc2945_state - driver instance specific data > * @regmap regmap object to access device registers > + * @r_sense_uohm current sense resistor value > */ > struct ltc2945_state { > struct regmap *regmap; > + u32 r_sense_uohm; > }; > > static inline bool is_power_reg(u8 reg) > @@ -101,9 +103,8 @@ 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 by and scale it with the configured > + * 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. > */ > @@ -112,10 +113,10 @@ static long long ltc2945_reg_to_val(struct device *dev, > u8 reg) > return ret; > if (control & CONTROL_MULT_SELECT) { > /* 25 mV * 25 uV = 0.625 uV resolution. */ > - val *= 625LL; > + val = DIV_ROUND_CLOSEST_ULL(val * 625LL * 1000, > st->r_sense_uohm); > } else { > /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ > - val = (val * 25LL) >> 1; > + val = DIV_ROUND_CLOSEST_ULL(val * 25LL * 1000, > st->r_sense_uohm) >> 1; > } > break; > case LTC2945_VIN_H: > @@ -140,13 +141,10 @@ static long long ltc2945_reg_to_val(struct device *dev, > u8 reg) > 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. > + * 25 uV resolution. Convert to current and scale it > + * with the value of the sense resistor. > */ > - val *= 25; > + val = DIV_ROUND_CLOSEST_ULL(val * 25 * 1000, st->r_sense_uohm); > break; > default: > return -EINVAL; > @@ -169,9 +167,8 @@ 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. > + * Convert to register value, scale it with the configured sense > + * resistor value, 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. > @@ -181,14 +178,10 @@ 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_ULL(val, 625); > + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 625 * > st->r_sense_uohm); > } else { > - /* > - * 0.5 mV * 25 uV = 0.0125 uV resolution. > - * Divide first to avoid overflow; > - * accept loss of accuracy. > - */ > - val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2; > + /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ > + val = DIV_ROUND_CLOSEST_ULL(val * 2 * 1000, 25 * > st->r_sense_uohm); > } > break; > case LTC2945_VIN_H: > @@ -213,13 +206,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 > reg, > 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. > + * 25 uV resolution. Convert to current and scale it > + * with the value of the sense resistor, in mA. > */ > - val = DIV_ROUND_CLOSEST_ULL(val, 25); > + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 25 * st->r_sense_uohm); > break; > default: > return -EINVAL; > @@ -475,6 +465,10 @@ static int ltc2945_probe(struct i2c_client *client) > return PTR_ERR(regmap); > } > > + if (device_property_read_u32(dev, "shunt-resistor-micro-ohms", > + &st->r_sense_uohm)) > + st->r_sense_uohm = 1000; > + Devicetree could set shunt-resistor-micro-ohms to 0, which would result in divide by 0 errors. Guenter > st->regmap = regmap; > > /* Clear faults */ > -- > 2.27.0 >
