linux-kernel - Re: [PATCH v3 2/3] staging: iio: ad7780: update voltage on read

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Message-ID: <b0c6d0356b83259e1adad3bf74cca3a56ae33847.camel@analog.com>
Date:   Thu, 1 Nov 2018 15:20:55 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "lars@...afoo.de" <lars@...afoo.de>,
        "knaack.h@....de" <knaack.h@....de>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "renatogeh@...il.com" <renatogeh@...il.com>,
        "giuliano.belinassi@....br" <giuliano.belinassi@....br>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "kernel-usp@...glegroups.com" <kernel-usp@...glegroups.com>
Subject: Re: [PATCH v3 2/3] staging: iio: ad7780: update voltage on read

On Thu, 2018-11-01 at 11:43 -0300, Renato Lui Geh wrote:
> The ad7780 driver previously did not read the correct device output, as
> it read an outdated value set at initialization. It now updates its
> voltage on read.
> 
> Signed-off-by: Renato Lui Geh <renatogeh@...il.com>
> ---
> Changes in v3:
> 	- removed initialization (int voltage_uv = 0)
> 	- returns error when voltage_uv is null
> 
>  drivers/staging/iio/adc/ad7780.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7780.c
> b/drivers/staging/iio/adc/ad7780.c
> index 91e016d534ed..f2a11e9424cd 100644
> --- a/drivers/staging/iio/adc/ad7780.c
> +++ b/drivers/staging/iio/adc/ad7780.c
> @@ -87,12 +87,16 @@ static int ad7780_read_raw(struct iio_dev *indio_dev,
>  			   long m)
>  {
>  	struct ad7780_state *st = iio_priv(indio_dev);
> +	int voltage_uv;
>  
>  	switch (m) {
>  	case IIO_CHAN_INFO_RAW:
>  		return ad_sigma_delta_single_conversion(indio_dev, chan,
> val);
>  	case IIO_CHAN_INFO_SCALE:
> -		*val = st->int_vref_mv * st->gain;
> +		voltage_uv = regulator_get_voltage(st->reg);
> +		if (!voltage_uv)

This looks wrong.
I admit this was done in the same way in the probe function, but that looks
a bit wrong as well.

Typically, the return value of `regulator_get_voltage()` would get checked
with:

ret = regulator_get_voltage(st->reg);
if (ret < 0)
   return ret;
*val = ret / 1000;

So, negative values are errors and zero & positive values are valid voltage
values.

> +			return -EINVAL;
> +		*val = (voltage_uv / 1000) * st->gain;
>  		*val2 = chan->scan_type.realbits - 1;
>  		return IIO_VAL_FRACTIONAL_LOG2;
>  	case IIO_CHAN_INFO_OFFSET: