Re: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Jonathan Cameron]

On Mon, 18 Dec 2017 10:02:44 +0100
Stefan Brüns  wrote:

> On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote:
> > Calibration register is used for calculating current register in
> > hardware according to datasheet:
> > current = shunt_volt * calib_register / 2048 (ina 226)
> > current = shunt_volt * calib_register / 4096 (ina 219)
> > 
> > Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> > order to avoid truncation error and provide best precision allowed
> > by shunt_voltage measurement. Make current scale value follow changes
> > of shunt_resistor from sysfs as calib_register value is now fixed.
> > 
> > Power_lsb value should also follow shunt_resistor changes as stated in
> > datasheet:
> > power_lsb = 25 * current_lsb (ina 226)
> > power_lsb = 20 * current_lsb (ina 219)
> > 
> > This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394
> > 
> > Signed-off-by: Maciej Purski   
> 
> Reviewed-by:  Stefan Brüns 
Applied to the togreg branch of iio.git and pushed out ass testing
for the autobuilders to play with it.

Thanks,

Jonathan
> 
> > ---
> > Changes in v4:
> > - fix comments
> > 
> > Changes in v3:
> > - remove variable current_lsb and calculate it on each read of current
> >   and power scale value
> > - update comments
> > 
> > Changes in v2:
> > - rebase on top of the latest next
> > - remove a redundant variable - power_lsb_uW
> > - fix comments
> > ---
> >  drivers/iio/adc/ina2xx-adc.c | 64
> > +++- 1 file changed, 33
> > insertions(+), 31 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> > index ddf8781..9e8ca12 100644
> > --- a/drivers/iio/adc/ina2xx-adc.c
> > +++ b/drivers/iio/adc/ina2xx-adc.c
> > @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
> > 
> >  struct ina2xx_config {
> > u16 config_default;
> > -   int calibration_factor;
> > +   int calibration_value;
> > int shunt_voltage_lsb;  /* nV */
> > int bus_voltage_shift;  /* position of lsb */
> > int bus_voltage_lsb;/* uV */
> > -   int power_lsb;  /* uW */
> > +   /* fixed relation between current and power lsb, uW/uA */
> > +   int power_lsb_factor;
> > enum ina2xx_ids chip_id;
> >  };
> > 
> > @@ -149,20 +150,20 @@ struct ina2xx_chip_info {
> >  static const struct ina2xx_config ina2xx_config[] = {
> > [ina219] = {
> > .config_default = INA219_CONFIG_DEFAULT,
> > -   .calibration_factor = 4096,
> > +   .calibration_value = 4096,
> > .shunt_voltage_lsb = 1,
> > .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
> > .bus_voltage_lsb = 4000,
> > -   .power_lsb = 2,
> > +   .power_lsb_factor = 20,
> > .chip_id = ina219,
> > },
> > [ina226] = {
> > .config_default = INA226_CONFIG_DEFAULT,
> > -   .calibration_factor = 512,
> > +   .calibration_value = 2048,
> > .shunt_voltage_lsb = 2500,
> > .bus_voltage_shift = 0,
> > .bus_voltage_lsb = 1250,
> > -   .power_lsb = 25000,
> > +   .power_lsb_factor = 25,
> > .chip_id = ina226,
> > },
> >  };
> > @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
> > *val2 = 1000;
> > return IIO_VAL_FRACTIONAL;
> > 
> > -   case INA2XX_POWER:
> > -   /* processed (mW) = raw*lsb (uW) / 1000 */
> > -   *val = chip->config->power_lsb;
> > -   *val2 = 1000;
> > +   case INA2XX_CURRENT:
> > +   /*
> > +* processed (mA) = raw * current_lsb (mA)
> > +* current_lsb (mA) = shunt_voltage_lsb (nV) /
> > +*shunt_resistor (uOhm)
> > +*/
> > +   *val = chip->config->shunt_voltage_lsb;
> > +   *val2 = chip->shunt_resistor_uohm;
> > return IIO_VAL_FRACTIONAL;
> > 
> > -   case INA2XX_CURRENT:
> > -   /* processed (mA) = raw (mA) */
> > -   *val = 1;
> > -   return IIO_VAL_INT;
> > +   case INA2XX_POWER:
> > +   /*
> > +* processed (mW) = raw * power_lsb (mW)
> > +* power_lsb (mW) = power_lsb_factor (mW/mA) *
> > +*  current_lsb (mA)
> > +*/
> > +   *val = chip->config->power_lsb_factor *
> > +  chip->config->shunt_voltage_lsb;
> > +   *val2 = chip->shunt_resistor_uohm;
> > +   return IIO_VAL_FRACTIONAL;
> > }
> > 
> > case IIO_CHAN_INFO_HARDWAREGAIN:
> > @@ -541,25 +552,21 @@ static ssize_t 

Re: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Jonathan Cameron]

On Mon, 18 Dec 2017 10:02:44 +0100
Stefan Brüns  wrote:

> On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote:
> > Calibration register is used for calculating current register in
> > hardware according to datasheet:
> > current = shunt_volt * calib_register / 2048 (ina 226)
> > current = shunt_volt * calib_register / 4096 (ina 219)
> > 
> > Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> > order to avoid truncation error and provide best precision allowed
> > by shunt_voltage measurement. Make current scale value follow changes
> > of shunt_resistor from sysfs as calib_register value is now fixed.
> > 
> > Power_lsb value should also follow shunt_resistor changes as stated in
> > datasheet:
> > power_lsb = 25 * current_lsb (ina 226)
> > power_lsb = 20 * current_lsb (ina 219)
> > 
> > This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394
> > 
> > Signed-off-by: Maciej Purski   
> 
> Reviewed-by:  Stefan Brüns 
Applied to the togreg branch of iio.git and pushed out ass testing
for the autobuilders to play with it.

Thanks,

Jonathan
> 
> > ---
> > Changes in v4:
> > - fix comments
> > 
> > Changes in v3:
> > - remove variable current_lsb and calculate it on each read of current
> >   and power scale value
> > - update comments
> > 
> > Changes in v2:
> > - rebase on top of the latest next
> > - remove a redundant variable - power_lsb_uW
> > - fix comments
> > ---
> >  drivers/iio/adc/ina2xx-adc.c | 64
> > +++- 1 file changed, 33
> > insertions(+), 31 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> > index ddf8781..9e8ca12 100644
> > --- a/drivers/iio/adc/ina2xx-adc.c
> > +++ b/drivers/iio/adc/ina2xx-adc.c
> > @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
> > 
> >  struct ina2xx_config {
> > u16 config_default;
> > -   int calibration_factor;
> > +   int calibration_value;
> > int shunt_voltage_lsb;  /* nV */
> > int bus_voltage_shift;  /* position of lsb */
> > int bus_voltage_lsb;/* uV */
> > -   int power_lsb;  /* uW */
> > +   /* fixed relation between current and power lsb, uW/uA */
> > +   int power_lsb_factor;
> > enum ina2xx_ids chip_id;
> >  };
> > 
> > @@ -149,20 +150,20 @@ struct ina2xx_chip_info {
> >  static const struct ina2xx_config ina2xx_config[] = {
> > [ina219] = {
> > .config_default = INA219_CONFIG_DEFAULT,
> > -   .calibration_factor = 4096,
> > +   .calibration_value = 4096,
> > .shunt_voltage_lsb = 1,
> > .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
> > .bus_voltage_lsb = 4000,
> > -   .power_lsb = 2,
> > +   .power_lsb_factor = 20,
> > .chip_id = ina219,
> > },
> > [ina226] = {
> > .config_default = INA226_CONFIG_DEFAULT,
> > -   .calibration_factor = 512,
> > +   .calibration_value = 2048,
> > .shunt_voltage_lsb = 2500,
> > .bus_voltage_shift = 0,
> > .bus_voltage_lsb = 1250,
> > -   .power_lsb = 25000,
> > +   .power_lsb_factor = 25,
> > .chip_id = ina226,
> > },
> >  };
> > @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
> > *val2 = 1000;
> > return IIO_VAL_FRACTIONAL;
> > 
> > -   case INA2XX_POWER:
> > -   /* processed (mW) = raw*lsb (uW) / 1000 */
> > -   *val = chip->config->power_lsb;
> > -   *val2 = 1000;
> > +   case INA2XX_CURRENT:
> > +   /*
> > +* processed (mA) = raw * current_lsb (mA)
> > +* current_lsb (mA) = shunt_voltage_lsb (nV) /
> > +*shunt_resistor (uOhm)
> > +*/
> > +   *val = chip->config->shunt_voltage_lsb;
> > +   *val2 = chip->shunt_resistor_uohm;
> > return IIO_VAL_FRACTIONAL;
> > 
> > -   case INA2XX_CURRENT:
> > -   /* processed (mA) = raw (mA) */
> > -   *val = 1;
> > -   return IIO_VAL_INT;
> > +   case INA2XX_POWER:
> > +   /*
> > +* processed (mW) = raw * power_lsb (mW)
> > +* power_lsb (mW) = power_lsb_factor (mW/mA) *
> > +*  current_lsb (mA)
> > +*/
> > +   *val = chip->config->power_lsb_factor *
> > +  chip->config->shunt_voltage_lsb;
> > +   *val2 = chip->shunt_resistor_uohm;
> > +   return IIO_VAL_FRACTIONAL;
> > }
> > 
> > case IIO_CHAN_INFO_HARDWAREGAIN:
> > @@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct
> > device *dev, }
> > 
> >  /*
> > - * Set current LSB to 

Re: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Stefan Brüns]

On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote:
> Calibration register is used for calculating current register in
> hardware according to datasheet:
> current = shunt_volt * calib_register / 2048 (ina 226)
> current = shunt_volt * calib_register / 4096 (ina 219)
> 
> Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> order to avoid truncation error and provide best precision allowed
> by shunt_voltage measurement. Make current scale value follow changes
> of shunt_resistor from sysfs as calib_register value is now fixed.
> 
> Power_lsb value should also follow shunt_resistor changes as stated in
> datasheet:
> power_lsb = 25 * current_lsb (ina 226)
> power_lsb = 20 * current_lsb (ina 219)
> 
> This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394
> 
> Signed-off-by: Maciej Purski 

Reviewed-by:  Stefan Brüns 

> ---
> Changes in v4:
> - fix comments
> 
> Changes in v3:
> - remove variable current_lsb and calculate it on each read of current
>   and power scale value
> - update comments
> 
> Changes in v2:
> - rebase on top of the latest next
> - remove a redundant variable - power_lsb_uW
> - fix comments
> ---
>  drivers/iio/adc/ina2xx-adc.c | 64
> +++- 1 file changed, 33
> insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> index ddf8781..9e8ca12 100644
> --- a/drivers/iio/adc/ina2xx-adc.c
> +++ b/drivers/iio/adc/ina2xx-adc.c
> @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
> 
>  struct ina2xx_config {
>   u16 config_default;
> - int calibration_factor;
> + int calibration_value;
>   int shunt_voltage_lsb;  /* nV */
>   int bus_voltage_shift;  /* position of lsb */
>   int bus_voltage_lsb;/* uV */
> - int power_lsb;  /* uW */
> + /* fixed relation between current and power lsb, uW/uA */
> + int power_lsb_factor;
>   enum ina2xx_ids chip_id;
>  };
> 
> @@ -149,20 +150,20 @@ struct ina2xx_chip_info {
>  static const struct ina2xx_config ina2xx_config[] = {
>   [ina219] = {
>   .config_default = INA219_CONFIG_DEFAULT,
> - .calibration_factor = 4096,
> + .calibration_value = 4096,
>   .shunt_voltage_lsb = 1,
>   .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
>   .bus_voltage_lsb = 4000,
> - .power_lsb = 2,
> + .power_lsb_factor = 20,
>   .chip_id = ina219,
>   },
>   [ina226] = {
>   .config_default = INA226_CONFIG_DEFAULT,
> - .calibration_factor = 512,
> + .calibration_value = 2048,
>   .shunt_voltage_lsb = 2500,
>   .bus_voltage_shift = 0,
>   .bus_voltage_lsb = 1250,
> - .power_lsb = 25000,
> + .power_lsb_factor = 25,
>   .chip_id = ina226,
>   },
>  };
> @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
>   *val2 = 1000;
>   return IIO_VAL_FRACTIONAL;
> 
> - case INA2XX_POWER:
> - /* processed (mW) = raw*lsb (uW) / 1000 */
> - *val = chip->config->power_lsb;
> - *val2 = 1000;
> + case INA2XX_CURRENT:
> + /*
> +  * processed (mA) = raw * current_lsb (mA)
> +  * current_lsb (mA) = shunt_voltage_lsb (nV) /
> +  *shunt_resistor (uOhm)
> +  */
> + *val = chip->config->shunt_voltage_lsb;
> + *val2 = chip->shunt_resistor_uohm;
>   return IIO_VAL_FRACTIONAL;
> 
> - case INA2XX_CURRENT:
> - /* processed (mA) = raw (mA) */
> - *val = 1;
> - return IIO_VAL_INT;
> + case INA2XX_POWER:
> + /*
> +  * processed (mW) = raw * power_lsb (mW)
> +  * power_lsb (mW) = power_lsb_factor (mW/mA) *
> +  *  current_lsb (mA)
> +  */
> + *val = chip->config->power_lsb_factor *
> +chip->config->shunt_voltage_lsb;
> + *val2 = chip->shunt_resistor_uohm;
> + return IIO_VAL_FRACTIONAL;
>   }
> 
>   case IIO_CHAN_INFO_HARDWAREGAIN:
> @@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct
> device *dev, }
> 
>  /*
> - * Set current LSB to 1mA, shunt is in uOhms
> - * (equation 13 in datasheet). We hardcode a Current_LSB
> - * of 1.0 x10-3. The only remaining parameter is RShunt.
> - * There is no need to expose the CALIBRATION register
> - * to the user for now. But we need to reset this 

Re: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Stefan Brüns]

On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote:
> Calibration register is used for calculating current register in
> hardware according to datasheet:
> current = shunt_volt * calib_register / 2048 (ina 226)
> current = shunt_volt * calib_register / 4096 (ina 219)
> 
> Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> order to avoid truncation error and provide best precision allowed
> by shunt_voltage measurement. Make current scale value follow changes
> of shunt_resistor from sysfs as calib_register value is now fixed.
> 
> Power_lsb value should also follow shunt_resistor changes as stated in
> datasheet:
> power_lsb = 25 * current_lsb (ina 226)
> power_lsb = 20 * current_lsb (ina 219)
> 
> This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394
> 
> Signed-off-by: Maciej Purski 

Reviewed-by:  Stefan Brüns 

> ---
> Changes in v4:
> - fix comments
> 
> Changes in v3:
> - remove variable current_lsb and calculate it on each read of current
>   and power scale value
> - update comments
> 
> Changes in v2:
> - rebase on top of the latest next
> - remove a redundant variable - power_lsb_uW
> - fix comments
> ---
>  drivers/iio/adc/ina2xx-adc.c | 64
> +++- 1 file changed, 33
> insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> index ddf8781..9e8ca12 100644
> --- a/drivers/iio/adc/ina2xx-adc.c
> +++ b/drivers/iio/adc/ina2xx-adc.c
> @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
> 
>  struct ina2xx_config {
>   u16 config_default;
> - int calibration_factor;
> + int calibration_value;
>   int shunt_voltage_lsb;  /* nV */
>   int bus_voltage_shift;  /* position of lsb */
>   int bus_voltage_lsb;/* uV */
> - int power_lsb;  /* uW */
> + /* fixed relation between current and power lsb, uW/uA */
> + int power_lsb_factor;
>   enum ina2xx_ids chip_id;
>  };
> 
> @@ -149,20 +150,20 @@ struct ina2xx_chip_info {
>  static const struct ina2xx_config ina2xx_config[] = {
>   [ina219] = {
>   .config_default = INA219_CONFIG_DEFAULT,
> - .calibration_factor = 4096,
> + .calibration_value = 4096,
>   .shunt_voltage_lsb = 1,
>   .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
>   .bus_voltage_lsb = 4000,
> - .power_lsb = 2,
> + .power_lsb_factor = 20,
>   .chip_id = ina219,
>   },
>   [ina226] = {
>   .config_default = INA226_CONFIG_DEFAULT,
> - .calibration_factor = 512,
> + .calibration_value = 2048,
>   .shunt_voltage_lsb = 2500,
>   .bus_voltage_shift = 0,
>   .bus_voltage_lsb = 1250,
> - .power_lsb = 25000,
> + .power_lsb_factor = 25,
>   .chip_id = ina226,
>   },
>  };
> @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
>   *val2 = 1000;
>   return IIO_VAL_FRACTIONAL;
> 
> - case INA2XX_POWER:
> - /* processed (mW) = raw*lsb (uW) / 1000 */
> - *val = chip->config->power_lsb;
> - *val2 = 1000;
> + case INA2XX_CURRENT:
> + /*
> +  * processed (mA) = raw * current_lsb (mA)
> +  * current_lsb (mA) = shunt_voltage_lsb (nV) /
> +  *shunt_resistor (uOhm)
> +  */
> + *val = chip->config->shunt_voltage_lsb;
> + *val2 = chip->shunt_resistor_uohm;
>   return IIO_VAL_FRACTIONAL;
> 
> - case INA2XX_CURRENT:
> - /* processed (mA) = raw (mA) */
> - *val = 1;
> - return IIO_VAL_INT;
> + case INA2XX_POWER:
> + /*
> +  * processed (mW) = raw * power_lsb (mW)
> +  * power_lsb (mW) = power_lsb_factor (mW/mA) *
> +  *  current_lsb (mA)
> +  */
> + *val = chip->config->power_lsb_factor *
> +chip->config->shunt_voltage_lsb;
> + *val2 = chip->shunt_resistor_uohm;
> + return IIO_VAL_FRACTIONAL;
>   }
> 
>   case IIO_CHAN_INFO_HARDWAREGAIN:
> @@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct
> device *dev, }
> 
>  /*
> - * Set current LSB to 1mA, shunt is in uOhms
> - * (equation 13 in datasheet). We hardcode a Current_LSB
> - * of 1.0 x10-3. The only remaining parameter is RShunt.
> - * There is no need to expose the CALIBRATION register
> - * to the user for now. But we need to reset this register
> - * if the user updates RShunt after driver 

[PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Maciej Purski]

Calibration register is used for calculating current register in
hardware according to datasheet:
current = shunt_volt * calib_register / 2048 (ina 226)
current = shunt_volt * calib_register / 4096 (ina 219)

Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
order to avoid truncation error and provide best precision allowed
by shunt_voltage measurement. Make current scale value follow changes
of shunt_resistor from sysfs as calib_register value is now fixed.

Power_lsb value should also follow shunt_resistor changes as stated in
datasheet:
power_lsb = 25 * current_lsb (ina 226)
power_lsb = 20 * current_lsb (ina 219)

This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394

Signed-off-by: Maciej Purski 

---
Changes in v4:
- fix comments

Changes in v3:
- remove variable current_lsb and calculate it on each read of current
  and power scale value
- update comments

Changes in v2:
- rebase on top of the latest next
- remove a redundant variable - power_lsb_uW
- fix comments
---
 drivers/iio/adc/ina2xx-adc.c | 64 +++-
 1 file changed, 33 insertions(+), 31 deletions(-)

diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
index ddf8781..9e8ca12 100644
--- a/drivers/iio/adc/ina2xx-adc.c
+++ b/drivers/iio/adc/ina2xx-adc.c
@@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
 
 struct ina2xx_config {
u16 config_default;
-   int calibration_factor;
+   int calibration_value;
int shunt_voltage_lsb;  /* nV */
int bus_voltage_shift;  /* position of lsb */
int bus_voltage_lsb;/* uV */
-   int power_lsb;  /* uW */
+   /* fixed relation between current and power lsb, uW/uA */
+   int power_lsb_factor;
enum ina2xx_ids chip_id;
 };
 
@@ -149,20 +150,20 @@ struct ina2xx_chip_info {
 static const struct ina2xx_config ina2xx_config[] = {
[ina219] = {
.config_default = INA219_CONFIG_DEFAULT,
-   .calibration_factor = 4096,
+   .calibration_value = 4096,
.shunt_voltage_lsb = 1,
.bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
.bus_voltage_lsb = 4000,
-   .power_lsb = 2,
+   .power_lsb_factor = 20,
.chip_id = ina219,
},
[ina226] = {
.config_default = INA226_CONFIG_DEFAULT,
-   .calibration_factor = 512,
+   .calibration_value = 2048,
.shunt_voltage_lsb = 2500,
.bus_voltage_shift = 0,
.bus_voltage_lsb = 1250,
-   .power_lsb = 25000,
+   .power_lsb_factor = 25,
.chip_id = ina226,
},
 };
@@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
*val2 = 1000;
return IIO_VAL_FRACTIONAL;
 
-   case INA2XX_POWER:
-   /* processed (mW) = raw*lsb (uW) / 1000 */
-   *val = chip->config->power_lsb;
-   *val2 = 1000;
+   case INA2XX_CURRENT:
+   /*
+* processed (mA) = raw * current_lsb (mA)
+* current_lsb (mA) = shunt_voltage_lsb (nV) /
+*shunt_resistor (uOhm)
+*/
+   *val = chip->config->shunt_voltage_lsb;
+   *val2 = chip->shunt_resistor_uohm;
return IIO_VAL_FRACTIONAL;
 
-   case INA2XX_CURRENT:
-   /* processed (mA) = raw (mA) */
-   *val = 1;
-   return IIO_VAL_INT;
+   case INA2XX_POWER:
+   /*
+* processed (mW) = raw * power_lsb (mW)
+* power_lsb (mW) = power_lsb_factor (mW/mA) *
+*  current_lsb (mA)
+*/
+   *val = chip->config->power_lsb_factor *
+  chip->config->shunt_voltage_lsb;
+   *val2 = chip->shunt_resistor_uohm;
+   return IIO_VAL_FRACTIONAL;
}
 
case IIO_CHAN_INFO_HARDWAREGAIN:
@@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct 
device *dev,
 }
 
 /*
- * Set current LSB to 1mA, shunt is in uOhms
- * (equation 13 in datasheet). We hardcode a Current_LSB
- * of 1.0 x10-3. The only remaining parameter is RShunt.
- * There is no need to expose the CALIBRATION register
- * to the user for now. But we need to reset this register
- * if the user updates RShunt after driver init, e.g upon
- * reading an EEPROM/Probe-type value.
+ * Calibration register is set to the best value, which eliminates
+ * truncation errors on calculating current register in 

[PATCH v4] iio: adc: ina2xx: Make calibration register value fixed

[Maciej Purski]

Calibration register is used for calculating current register in
hardware according to datasheet:
current = shunt_volt * calib_register / 2048 (ina 226)
current = shunt_volt * calib_register / 4096 (ina 219)

Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
order to avoid truncation error and provide best precision allowed
by shunt_voltage measurement. Make current scale value follow changes
of shunt_resistor from sysfs as calib_register value is now fixed.

Power_lsb value should also follow shunt_resistor changes as stated in
datasheet:
power_lsb = 25 * current_lsb (ina 226)
power_lsb = 20 * current_lsb (ina 219)

This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394

Signed-off-by: Maciej Purski 

---
Changes in v4:
- fix comments

Changes in v3:
- remove variable current_lsb and calculate it on each read of current
  and power scale value
- update comments

Changes in v2:
- rebase on top of the latest next
- remove a redundant variable - power_lsb_uW
- fix comments
---
 drivers/iio/adc/ina2xx-adc.c | 64 +++-
 1 file changed, 33 insertions(+), 31 deletions(-)

diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
index ddf8781..9e8ca12 100644
--- a/drivers/iio/adc/ina2xx-adc.c
+++ b/drivers/iio/adc/ina2xx-adc.c
@@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
 
 struct ina2xx_config {
u16 config_default;
-   int calibration_factor;
+   int calibration_value;
int shunt_voltage_lsb;  /* nV */
int bus_voltage_shift;  /* position of lsb */
int bus_voltage_lsb;/* uV */
-   int power_lsb;  /* uW */
+   /* fixed relation between current and power lsb, uW/uA */
+   int power_lsb_factor;
enum ina2xx_ids chip_id;
 };
 
@@ -149,20 +150,20 @@ struct ina2xx_chip_info {
 static const struct ina2xx_config ina2xx_config[] = {
[ina219] = {
.config_default = INA219_CONFIG_DEFAULT,
-   .calibration_factor = 4096,
+   .calibration_value = 4096,
.shunt_voltage_lsb = 1,
.bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
.bus_voltage_lsb = 4000,
-   .power_lsb = 2,
+   .power_lsb_factor = 20,
.chip_id = ina219,
},
[ina226] = {
.config_default = INA226_CONFIG_DEFAULT,
-   .calibration_factor = 512,
+   .calibration_value = 2048,
.shunt_voltage_lsb = 2500,
.bus_voltage_shift = 0,
.bus_voltage_lsb = 1250,
-   .power_lsb = 25000,
+   .power_lsb_factor = 25,
.chip_id = ina226,
},
 };
@@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
*val2 = 1000;
return IIO_VAL_FRACTIONAL;
 
-   case INA2XX_POWER:
-   /* processed (mW) = raw*lsb (uW) / 1000 */
-   *val = chip->config->power_lsb;
-   *val2 = 1000;
+   case INA2XX_CURRENT:
+   /*
+* processed (mA) = raw * current_lsb (mA)
+* current_lsb (mA) = shunt_voltage_lsb (nV) /
+*shunt_resistor (uOhm)
+*/
+   *val = chip->config->shunt_voltage_lsb;
+   *val2 = chip->shunt_resistor_uohm;
return IIO_VAL_FRACTIONAL;
 
-   case INA2XX_CURRENT:
-   /* processed (mA) = raw (mA) */
-   *val = 1;
-   return IIO_VAL_INT;
+   case INA2XX_POWER:
+   /*
+* processed (mW) = raw * power_lsb (mW)
+* power_lsb (mW) = power_lsb_factor (mW/mA) *
+*  current_lsb (mA)
+*/
+   *val = chip->config->power_lsb_factor *
+  chip->config->shunt_voltage_lsb;
+   *val2 = chip->shunt_resistor_uohm;
+   return IIO_VAL_FRACTIONAL;
}
 
case IIO_CHAN_INFO_HARDWAREGAIN:
@@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct 
device *dev,
 }
 
 /*
- * Set current LSB to 1mA, shunt is in uOhms
- * (equation 13 in datasheet). We hardcode a Current_LSB
- * of 1.0 x10-3. The only remaining parameter is RShunt.
- * There is no need to expose the CALIBRATION register
- * to the user for now. But we need to reset this register
- * if the user updates RShunt after driver init, e.g upon
- * reading an EEPROM/Probe-type value.
+ * Calibration register is set to the best value, which eliminates
+ * truncation errors on calculating current register in hardware.
+ * According to