Re: [PATCH] iio: adc: nau7802: Expose possible gains in sysfs

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 18/05/2016 at 17:16:18 +0200, Quentin Schulz wrote :
>
> The Nuvoton NAU7802 ADC is able to adjust its gain but prior knowledge of
> its possible values was required to adjust it. Users had to guess the
> possible gain values based on the ADC datasheet or on this driver's code.
> 
> This exposes the possible values in the in_voltage_scale_available file of
> each nau7802 ADC device. The gain is set for the whole ADC and is therefore
> not configurable by channel. Thus, there exists only one
> in_voltage_scale_available file for each nau7802 ADC device even if it has
> two separate channels.
> 
> Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

> ---
> 
> There exists two files to set the gain: in_voltageX_scale_available and
> in_voltage-voltage_scale_available. What are the differences between those
> two? What are the use cases for each? Which one should I have used?
> 
>  drivers/iio/adc/nau7802.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/iio/adc/nau7802.c b/drivers/iio/adc/nau7802.c
> index e525aa6..57365c5 100644
> --- a/drivers/iio/adc/nau7802.c
> +++ b/drivers/iio/adc/nau7802.c
> @@ -79,10 +79,29 @@ static const struct iio_chan_spec nau7802_chan_array[] = {
>  static const u16 nau7802_sample_freq_avail[] = {10, 20, 40, 80,
>  						10, 10, 10, 320};
>  
> +static ssize_t nau7802_show_scales(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	struct nau7802_state *st = iio_priv(dev_to_iio_dev(dev));
> +	int i, len = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(st->scale_avail); i++)
> +		len += scnprintf(buf + len, PAGE_SIZE - len, "0.%09d ",
> +				 st->scale_avail[i]);
> +
> +	buf[len-1] = '\n';
> +
> +	return len;
> +}
> +
>  static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("10 40 80 320");
>  
> +static IIO_DEVICE_ATTR(in_voltage_scale_available, S_IRUGO, nau7802_show_scales,
> +		       NULL, 0);
> +
>  static struct attribute *nau7802_attributes[] = {
>  	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> +	&iio_dev_attr_in_voltage_scale_available.dev_attr.attr,
>  	NULL
>  };
>  
> -- 
> 2.5.0
> 

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com