On Thu, Jan 07, 2021 at 12:34:16PM +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. > Also, the maximum power and current that can be represented by the driver > are scaled with the value of the sense resistor. >
In a way you are correct, but that applies to all hwmon drivers, not just to this one. A solution which only applies to a single driver doesn't solve the underlying problem, which would be the desire or need to provide kernel-based scaling for hwmon drivers. As such, I am not inclined to accept this patch. We should think about a generic solution instead. Note that this patch doesn't compile on 32-bit targets. Thanks, Guenter > Signed-off-by: Alexandru Ardelean <[email protected]> > --- > drivers/hwmon/ltc2945.c | 60 ++++++++++++++++++++++++++--------------- > 1 file changed, 39 insertions(+), 21 deletions(-) > > diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c > index 41df2c8b7673..e60b15832b0e 100644 > --- a/drivers/hwmon/ltc2945.c > +++ b/drivers/hwmon/ltc2945.c > @@ -70,9 +70,15 @@ > /** > * struct ltc2945_state - driver instance specific data > * @regmap: regmap object to access device registers > + * @max_power_uw: maximum power that can be represented based on sense > resistor > + * @max_current_ma: maximum current that can be represented based on sense > resistor > + * @r_sense_mohm: current sense resistor value > */ > struct ltc2945_state { > struct regmap *regmap; > + u32 max_power_uw; > + u32 max_current_ma; > + u32 r_sense_mohm; > }; > > static inline bool is_power_reg(u8 reg) > @@ -110,9 +116,8 @@ 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. > */ > @@ -126,6 +131,7 @@ 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 /= st->r_sense_mohm; > break; > case LTC2945_VIN_H: > case LTC2945_MAX_VIN_H: > @@ -149,13 +155,11 @@ 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 /= st->r_sense_mohm; > break; > default: > return -EINVAL; > @@ -163,7 +167,8 @@ static long long ltc2945_reg_to_val(struct device *dev, > u8 reg) > return val; > } > > -static unsigned long ltc2945_val_clamp(u8 reg, unsigned long val) > +static unsigned long ltc2945_val_clamp(struct ltc2945_state *st, u8 reg, > + unsigned long val) > { > switch (reg) { > case LTC2945_POWER_H: > @@ -171,8 +176,7 @@ static unsigned long ltc2945_val_clamp(u8 reg, unsigned > long val) > case LTC2945_MIN_POWER_H: > case LTC2945_MAX_POWER_THRES_H: > case LTC2945_MIN_POWER_THRES_H: > - /* No sense in clamping now, LTC2945_POWER_FULL_SCALE_UW is > larger than UINT32_MAX */ > - return val; > + return clamp_val(val, 0, st->max_power_uw); > case LTC2945_VIN_H: > case LTC2945_MAX_VIN_H: > case LTC2945_MIN_VIN_H: > @@ -190,7 +194,7 @@ static unsigned long ltc2945_val_clamp(u8 reg, unsigned > long val) > case LTC2945_MIN_SENSE_H: > case LTC2945_MAX_SENSE_THRES_H: > case LTC2945_MIN_SENSE_THRES_H: > - return clamp_val(val, 0, LTC2945_SENSE_FULL_SCALE_MA); > + return clamp_val(val, 0, st->max_current_ma); > default: > /* > * This is unlikely to happen, and if it does, it should > @@ -215,9 +219,8 @@ 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. > @@ -236,6 +239,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, > */ > val = DIV_ROUND_CLOSEST(val, 25) * 2; > } > + val *= st->r_sense_mohm; > break; > case LTC2945_VIN_H: > case LTC2945_MAX_VIN_H: > @@ -259,12 +263,10 @@ 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 *= st->r_sense_mohm; > val = DIV_ROUND_CLOSEST(val, 25); > break; > default: > @@ -303,7 +305,7 @@ static ssize_t ltc2945_value_store(struct device *dev, > if (ret) > return ret; > > - val = ltc2945_val_clamp(reg, val); > + val = ltc2945_val_clamp(st, reg, val); > > /* convert to register value, then clamp and write result */ > regval = ltc2945_val_to_reg(dev, reg, val); > @@ -512,6 +514,7 @@ static int ltc2945_probe(struct i2c_client *client) > struct ltc2945_state *st; > struct device *hwmon_dev; > struct regmap *regmap; > + u64 val64; > > st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL); > if (!st) > @@ -523,7 +526,22 @@ 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_mohm)) > + st->r_sense_mohm = 1000; > + > + if (st->r_sense_mohm < 1000) { > + dev_err(dev, "Value too small for sense resistor, minimum > 1000\n"); > + return -EINVAL; > + } > + st->r_sense_mohm /= 1000; > + > st->regmap = regmap; > + val64 = LTC2945_POWER_FULL_SCALE_UW / st->r_sense_mohm; > + /* clamp power to ULONG_MAX, since we represent it on 32 bits */ > + st->max_power_uw = clamp_val(val64, 0, ULONG_MAX); > + > + st->max_current_ma = LTC2945_SENSE_FULL_SCALE_MA / st->r_sense_mohm; > > /* Clear faults */ > regmap_write(regmap, LTC2945_FAULT, 0x00); > -- > 2.17.1 >
