Re: [PATCH 1/2] staging: iio: ad7606: replace range/range_available with corresponding scale

[Eva Rachel Retuya <eraretuya@gmail.com>]

Hello, 

Thanks for explaining it. Now I understand better why read_raw is
formatted in that manner. I have some questions in-line:

On Fri, Nov 11, 2016 at 03:18:37PM +0100, Lars-Peter Clausen wrote:
> On 11/11/2016 07:34 AM, Eva Rachel Retuya wrote:
> > Eliminate the non-standard attribute in_voltage_range and move its
> > functionality under the scale attribute. read_raw() has been taken care
> > of previously so only write_raw() is handled here.
> > 
> > Additionally, rename the attribute in_voltage_range_available into
> > in_voltage_scale_available.
> > 
> > Suggested-by: Lars-Peter Clausen <lars@metafoo.de>
> > Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
> 
> Hi,
> 
> Thanks for the patch. Unfortunately this is not quite this straight forward.
> 
> The scale is what you multiply the raw with to get the value in the standard
> IIO unit. Range as implemented in this driver is the maximum output voltage.
> 
> To get the scale we need to look at the transfer function of the ADC [1].
> The transfer function tells us that 1 LSB is 305uV for the 10V range and
> 152uV for the 5V range.

Instead of 10000 and 5000, these will be the values for the
scale_available attribute?

> 
> More specifically this is $RANGE*2/2**16 (times two since the ADC is bipolar).
> 
> Since the default unit for IIO is mV for voltages we need to multiply this
> by 1000.
> 
> The other thing we need to handle is the case where the RANGE pin is not
> connected to a GPIO but either hardwired to 1 or 0. Which we need to handle
> somehow.

Will this be on the same patch or a separate one? Can you please give a
hint on how to check if it is hardwired?

Eva

> 
> [1]
> http://www.analog.com/media/en/technical-documentation/data-sheets/AD7606_7606-6_7606-4.pdf#page=23
> (right bottom)
> 
> > ---
> >  drivers/staging/iio/adc/ad7606.c | 56 ++++++++++++----------------------------
> >  1 file changed, 16 insertions(+), 40 deletions(-)
> > 
> > diff --git a/drivers/staging/iio/adc/ad7606.c b/drivers/staging/iio/adc/ad7606.c
> > index 4531908..cceb18c 100644
> > --- a/drivers/staging/iio/adc/ad7606.c
> > +++ b/drivers/staging/iio/adc/ad7606.c
> > @@ -161,42 +161,7 @@ static int ad7606_read_raw(struct iio_dev *indio_dev,
> >  	return -EINVAL;
> >  }
> >  
> > -static ssize_t ad7606_show_range(struct device *dev,
> > -				 struct device_attribute *attr, char *buf)
> > -{
> > -	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > -	struct ad7606_state *st = iio_priv(indio_dev);
> > -
> > -	return sprintf(buf, "%u\n", st->range);
> > -}
> > -
> > -static ssize_t ad7606_store_range(struct device *dev,
> > -				  struct device_attribute *attr,
> > -				  const char *buf, size_t count)
> > -{
> > -	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > -	struct ad7606_state *st = iio_priv(indio_dev);
> > -	unsigned long lval;
> > -	int ret;
> > -
> > -	ret = kstrtoul(buf, 10, &lval);
> > -	if (ret)
> > -		return ret;
> > -
> > -	if (!(lval == 5000 || lval == 10000))
> > -		return -EINVAL;
> > -
> > -	mutex_lock(&indio_dev->mlock);
> > -	gpiod_set_value(st->gpio_range, lval == 10000);
> > -	st->range = lval;
> > -	mutex_unlock(&indio_dev->mlock);
> > -
> > -	return count;
> > -}
> > -
> > -static IIO_DEVICE_ATTR(in_voltage_range, S_IRUGO | S_IWUSR,
> > -		       ad7606_show_range, ad7606_store_range, 0);
> > -static IIO_CONST_ATTR(in_voltage_range_available, "5000 10000");
> > +static IIO_CONST_ATTR(in_voltage_scale_available, "5000 10000");
> >  
> >  static int ad7606_oversampling_get_index(unsigned int val)
> >  {
> > @@ -221,6 +186,19 @@ static int ad7606_write_raw(struct iio_dev *indio_dev,
> >  	int ret;
> >  
> >  	switch (mask) {
> > +	case IIO_CHAN_INFO_SCALE:
> > +		if (val2)
> > +			return -EINVAL;
> > +
> > +		if (!(val == 5000 || val == 10000))
> > +			return -EINVAL;
> > +
> > +		mutex_lock(&indio_dev->mlock);
> > +		gpiod_set_value(st->gpio_range, val == 10000);
> > +		st->range = val;
> > +		mutex_unlock(&indio_dev->mlock);
> > +
> > +		return 0;
> >  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> >  		if (val2)
> >  			return -EINVAL;
> > @@ -247,8 +225,7 @@ static int ad7606_write_raw(struct iio_dev *indio_dev,
> >  static IIO_CONST_ATTR(oversampling_ratio_available, "1 2 4 8 16 32 64");
> >  
> >  static struct attribute *ad7606_attributes_os_and_range[] = {
> > -	&iio_dev_attr_in_voltage_range.dev_attr.attr,
> > -	&iio_const_attr_in_voltage_range_available.dev_attr.attr,
> > +	&iio_const_attr_in_voltage_scale_available.dev_attr.attr,
> >  	&iio_const_attr_oversampling_ratio_available.dev_attr.attr,
> >  	NULL,
> >  };
> > @@ -267,8 +244,7 @@ static const struct attribute_group ad7606_attribute_group_os = {
> >  };
> >  
> >  static struct attribute *ad7606_attributes_range[] = {
> > -	&iio_dev_attr_in_voltage_range.dev_attr.attr,
> > -	&iio_const_attr_in_voltage_range_available.dev_attr.attr,
> > +	&iio_const_attr_in_voltage_scale_available.dev_attr.attr,
> >  	NULL,
> >  };
> >  
> > 
>