From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: =?iso-8859-1?Q?Br=FCns=2C_Stefan?= To: Maciej Purski CC: Jonathan Cameron , "linux-iio@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-hwmon@vger.kernel.org" , Peter Meerwald-Stadler , Lars-Peter Clausen , Hartmut Knaack , "Jean Delvare" , Guenter Roeck , "Marek Szyprowski" , Bartlomiej Zolnierkiewicz Subject: Re: [PATCH v2] iio: adc: ina2xx: Make calibration register value fixed Date: Thu, 7 Dec 2017 16:10:40 +0000 Message-ID: <3656355.n9BamPbOAV@sbruens-linux> References: <1512648167-11482-1-git-send-email-m.purski@samsung.com> In-Reply-To: <1512648167-11482-1-git-send-email-m.purski@samsung.com> Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 List-ID: On Donnerstag, 7. Dezember 2017 13:02:47 CET Maciej Purski wrote:=0A= > Calibration register is used for calculating current register in=0A= > hardware according to datasheet:=0A= > current =3D shunt_volt * calib_register / 2048 (ina 226)=0A= > current =3D shunt_volt * calib_register / 4096 (ina 219)=0A= > =0A= > Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in=0A= > order to avoid truncation error and provide best precision allowed=0A= > by shunt_voltage measurement. Make current scale value follow changes=0A= > of shunt_resistor from sysfs as calib_register value is now fixed.=0A= > =0A= > Power_lsb value should also follow shunt_resistor changes as stated in=0A= > datasheet:=0A= > power_lsb =3D 25 * current_lsb (ina 226)=0A= > power_lsb =3D 20 * current_lsb (ina 219)=0A= > =0A= > This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394=0A= > =0A= > Signed-off-by: Maciej Purski =0A= > =0A= > ---=0A= > Changes in v2:=0A= > - rebase on top of the latest next=0A= > - remove a redundant variable - power_lsb_uW=0A= > - fix comments=0A= > ---=0A= > drivers/iio/adc/ina2xx-adc.c | 58=0A= > +++++++++++++++++++++++--------------------- 1 file changed, 31=0A= > insertions(+), 27 deletions(-)=0A= > =0A= > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c= =0A= > index ddf8781..3e4972f 100644=0A= > --- a/drivers/iio/adc/ina2xx-adc.c=0A= > +++ b/drivers/iio/adc/ina2xx-adc.c=0A= > @@ -124,11 +124,11 @@ enum ina2xx_ids { ina219, ina226 };=0A= > =0A= > struct ina2xx_config {=0A= > u16 config_default;=0A= > - int calibration_factor;=0A= > + int calibration_value;=0A= > int shunt_voltage_lsb; /* nV */=0A= > int bus_voltage_shift; /* position of lsb */=0A= > int bus_voltage_lsb; /* uV */=0A= > - int power_lsb; /* uW */=0A= > + int power_lsb_factor;=0A= > enum ina2xx_ids chip_id;=0A= > };=0A= > =0A= > @@ -138,6 +138,7 @@ struct ina2xx_chip_info {=0A= > const struct ina2xx_config *config;=0A= > struct mutex state_lock;=0A= > unsigned int shunt_resistor_uohm;=0A= > + unsigned int current_lsb_uA;=0A= =0A= I don't think you need current_lsb_uA, see below ...=0A= =0A= > int avg;=0A= > int int_time_vbus; /* Bus voltage integration time uS */=0A= > int int_time_vshunt; /* Shunt voltage integration time uS */=0A= > @@ -149,20 +150,20 @@ struct ina2xx_chip_info {=0A= > static const struct ina2xx_config ina2xx_config[] =3D {=0A= > [ina219] =3D {=0A= > .config_default =3D INA219_CONFIG_DEFAULT,=0A= > - .calibration_factor =3D 40960000,=0A= > + .calibration_value =3D 4096,=0A= > .shunt_voltage_lsb =3D 10000,=0A= > .bus_voltage_shift =3D INA219_BUS_VOLTAGE_SHIFT,=0A= > .bus_voltage_lsb =3D 4000,=0A= > - .power_lsb =3D 20000,=0A= > + .power_lsb_factor =3D 20,=0A= > .chip_id =3D ina219,=0A= > },=0A= > [ina226] =3D {=0A= > .config_default =3D INA226_CONFIG_DEFAULT,=0A= > - .calibration_factor =3D 5120000,=0A= > + .calibration_value =3D 2048,=0A= > .shunt_voltage_lsb =3D 2500,=0A= > .bus_voltage_shift =3D 0,=0A= > .bus_voltage_lsb =3D 1250,=0A= > - .power_lsb =3D 25000,=0A= > + .power_lsb_factor =3D 25,=0A= > .chip_id =3D ina226,=0A= > },=0A= > };=0A= > @@ -229,14 +230,16 @@ static int ina2xx_read_raw(struct iio_dev *indio_de= v,=0A= > =0A= > case INA2XX_POWER:=0A= > /* processed (mW) =3D raw*lsb (uW) / 1000 */=0A= > - *val =3D chip->config->power_lsb;=0A= > + *val =3D chip->config->power_lsb_factor *=0A= > + chip->current_lsb_uA;=0A= > *val2 =3D 1000;=0A= > return IIO_VAL_FRACTIONAL;=0A= > =0A= > case INA2XX_CURRENT:=0A= > - /* processed (mA) =3D raw (mA) */=0A= > - *val =3D 1;=0A= > - return IIO_VAL_INT;=0A= > + /* processed (mA) =3D raw*lsb (uA) / 1000 */=0A= > + *val =3D chip->current_lsb_uA;=0A= > + *val2 =3D 1000;=0A= =0A= ... this is the only place where current_lsb_uA is used ...=0A= =0A= > + return IIO_VAL_FRACTIONAL;=0A= > }=0A= > =0A= > case IIO_CHAN_INFO_HARDWAREGAIN:=0A= > @@ -541,28 +544,34 @@ static ssize_t ina2xx_allow_async_readout_store(str= uct=0A= > device *dev, }=0A= > =0A= > /*=0A= > - * Set current LSB to 1mA, shunt is in uOhms=0A= > - * (equation 13 in datasheet). We hardcode a Current_LSB=0A= > - * of 1.0 x10-3. The only remaining parameter is RShunt.=0A= > - * There is no need to expose the CALIBRATION register=0A= > - * to the user for now. But we need to reset this register=0A= > - * if the user updates RShunt after driver init, e.g upon=0A= > - * reading an EEPROM/Probe-type value.=0A= > + * Calibration register is set to the best value, which eliminates=0A= > + * truncation errors on calculating current register in hardware.=0A= > + * According to datasheet (INA 226: eq. 3, INA219: eq. 4) the best value= s=0A= > + * are 2048 for ina226 and 4096 for ina219. They are hardcoded as=0A= > + * calibration_value.=0A= > */=0A= > static int ina2xx_set_calibration(struct ina2xx_chip_info *chip)=0A= > {=0A= > - u16 regval =3D DIV_ROUND_CLOSEST(chip->config->calibration_factor,=0A= > - chip->shunt_resistor_uohm);=0A= > -=0A= > - return regmap_write(chip->regmap, INA2XX_CALIBRATION, regval);=0A= > + return regmap_write(chip->regmap, INA2XX_CALIBRATION,=0A= > + chip->config->calibration_value);=0A= > }=0A= > =0A= > +/*=0A= > + * In order to keep calibration register value fixed, the product=0A= > + * of current_lsb and shunt_resistor should also be fixed and equal=0A= > + * to shunt_voltage_lsb =3D 1 / shunt_div multiplied by 10^9 in order=0A= > + * to keep the scale.=0A= > + */=0A= > static int set_shunt_resistor(struct ina2xx_chip_info *chip, unsigned in= t=0A= > val) {=0A= > - if (val <=3D 0 || val > chip->config->calibration_factor)=0A= > + unsigned int dividend =3D DIV_ROUND_CLOSEST(1000000000,=0A= > + chip->config->shunt_div);=0A= > +=0A= > + if (val <=3D 0 || val > dividend)=0A= > return -EINVAL;=0A= > =0A= > chip->shunt_resistor_uohm =3D val;=0A= > + chip->current_lsb_uA =3D DIV_ROUND_CLOSEST(dividend, val);=0A= =0A= 1st: shunt_div no longer exists, but shunt_voltage_lsb[nV], so this code do= es =0A= not even compile ...=0A= =0A= This function does two things - range check and calculation of the =0A= curren_lsb_uA auxiliary variable.=0A= =0A= Lets start with the second part:=0A= =0A= read_raw returns the IIO_VAL_FRACTIONAL=0A= val / val2 =3D current_lsb_uA / 1000 (1)=0A= =0A= =0A= from set_shunt_resistor(...):=0A= =0A= dividend =3D 1e9 / shunt_div (2)=0A= current_lsb_uA =3D dividend / shunt_resistor_uohm (3)=0A= =0A= shunt_div no longer exists, but can be substituted:=0A= shunt_div =3D 1e6 / shunt_voltage_lsb (4)=0A= =0A= substituting (2), (3) and (4) in (1), we end up with=0A= =0A= val / val2 =3D 1e9 / (shunt_div * shunt_resistor_uohm * 1000)=0A= =0A= =3D> val / val2 =3D 1e6 / ((1e6 / shunt_voltage_lsb) * shunt_resistor_uohm= )=0A= =3D> val / val2 =3D shunt_voltage_lsb / shunt_resistor_uohm=0A= =3D> [mA] =3D [nV] / [uOhm]=0A= =0A= The auxiliary variable is gone, as are the two DIV_ROUND_CLOSEST calls.=0A= =0A= =0A= Part 2, range check:=0A= =0A= lower bound is obviously 1 uOhm. The upper bound is only limited by=0A= typeof(val2) and typeof(shunt_resistor_uohm), both are ints.=0A= =0A= so the range check can be simplified to=0A= =0A= if (val =3D=3D 0 || val > INT_MAX)=0A= return -EINVAL=0A= =0A= Kind regards,=0A= =0A= Stefan=0A= =0A=