Re: [PATCH 1/2] staging: iio: ad7780: Add gain & filter gpio support

["Popa, Stefan Serban" <StefanSerban.Popa@analog.com>]

On Mi, 2018-11-28 at 16:15 -0200, Giuliano Belinassi wrote:
> Previously, the AD7780 driver only supported gpio for the 'powerdown'
> pin. This commit adds suppport for the 'gain' and 'filter' pin.
> 
> Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
> ---
> Changes in v2:
>     - Now this patch is part of the patchset that aims to remove ad7780
> out of staging. https://marc.info/?l=linux-iio&m=154282349808890&w=2
>     - Also, now it reads voltage and filter values from the userspace
> instead of gpio pin states.

Hello,
Please see bellow.

> 
>  drivers/staging/iio/adc/ad7780.c       | 78 ++++++++++++++++++++++++--
>  include/linux/iio/adc/ad_sigma_delta.h |  5 ++
>  2 files changed, 79 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7780.c
> b/drivers/staging/iio/adc/ad7780.c
> index c4a85789c2db..05979a79fda3 100644
> --- a/drivers/staging/iio/adc/ad7780.c
> +++ b/drivers/staging/iio/adc/ad7780.c
> @@ -39,6 +39,12 @@
>  #define AD7170_PATTERN		(AD7780_PAT0 | AD7170_PAT2)
>  #define AD7170_PATTERN_MASK	(AD7780_PAT0 | AD7780_PAT1 |
> AD7170_PAT2)
>  
> +#define AD7780_GAIN_GPIO	0
> +#define AD7780_FILTER_GPIO	1
> +
> +#define AD7780_GAIN_MIDPOINT	64
> +#define AD7780_FILTER_MIDPOINT	13350
> +
>  struct ad7780_chip_info {
>  	struct iio_chan_spec	channel;
>  	unsigned int		pattern_mask;
> @@ -50,6 +56,8 @@ struct ad7780_state {
>  	const struct ad7780_chip_info	*chip_info;
>  	struct regulator		*reg;
>  	struct gpio_desc		*powerdown_gpio;
> +	struct gpio_desc		*gain_gpio;
> +	struct gpio_desc		*filter_gpio;
>  	unsigned int	gain;
>  
>  	struct ad_sigma_delta sd;
> @@ -115,18 +123,65 @@ static int ad7780_read_raw(struct iio_dev
> *indio_dev,
>  	return -EINVAL;
>  }
>  
> +static int ad7780_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val,
> +			    int val2,
> +			    long m)
> +{
> +	struct ad7780_state *st = iio_priv(indio_dev);
> +	const struct ad7780_chip_info *chip_info = st->chip_info;
> +	int uvref, gain;
> +	unsigned int full_scale;
> +
> +	if (!chip_info->is_ad778x)
> +		return 0;
> +
> +	switch (m) {
> +	case IIO_CHAN_INFO_SCALE:
> +		if (val != 0)
> +			return -EINVAL;
> +
> +		uvref = regulator_get_voltage(st->reg);

regulator_get_voltage() has already been called in the probe function and
the result is stored in st->int_vref_mv.
My suggestion would be to use a local vref variable declared as unsigned
int. It is my fault that I haven't explained correctly in the previous
email, but you need to multiply vref_mv with 1000000LL in order to get the
right precision: vref = st->int_vref_mv * 1000000LL. Afterwards you will be
able to perform the divisions.
> +
> +		if (uvref < 0)
> +			return uvref;
> +
> +		full_scale = 1 << (chip_info->channel.scan_type.realbits 
> - 1);
> +		gain = DIV_ROUND_CLOSEST(uvref, full_scale);
> +		gain = DIV_ROUND_CLOSEST(gain, val2);
> +
> +		gpiod_set_value(st->gain_gpio, gain <
> AD7780_GAIN_MIDPOINT ? 0 : 1);

Once the gain is set, you can store it in st->gain variable.

> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		if (val2 != 0)
> +			return -EINVAL;
> +
> +		gpiod_set_value(st->filter_gpio, val <
> AD7780_FILTER_MIDPOINT ? 0 : 1);

This is probably fine, although I am not a big fan of the ternary operator.
A simple if else statement would do. However, I don't feel strongly about
it, so feel free to disagree. 

> +	break;
> +	}
> +
> +	return 0;
> +}
> +
>  static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
>  				     unsigned int raw_sample)
>  {
>  	struct ad7780_state *st = ad_sigma_delta_to_ad7780(sigma_delta);
>  	const struct ad7780_chip_info *chip_info = st->chip_info;
> +	int val;
>  
>  	if ((raw_sample & AD7780_ERR) ||
>  	    ((raw_sample & chip_info->pattern_mask) != chip_info-
> >pattern))
>  		return -EIO;
>  
>  	if (chip_info->is_ad778x) {
> -		if (raw_sample & AD7780_GAIN)
> +		val = raw_sample & AD7780_GAIN;
> +
> +		if (val != gpiod_get_value(st->gain_gpio))
> +			return -EIO;

It is not obvious to me what is the point of this check. Maybe you can add
a comment?

> +
> +		if (val)
>  			st->gain = 1;
>  		else
>  			st->gain = 128;

Do we still need this? I am not convinced. 

> @@ -141,18 +196,20 @@ static const struct ad_sigma_delta_info
> ad7780_sigma_delta_info = {
>  	.has_registers = false,
>  };
>  
> -#define AD7780_CHANNEL(bits, wordsize) \
> +#define AD7170_CHANNEL(bits, wordsize) \
>  	AD_SD_CHANNEL_NO_SAMP_FREQ(1, 0, 0, bits, 32, wordsize - bits)
> +#define AD7780_CHANNEL(bits, wordsize) \
> +	AD_SD_CHANNEL_GAIN_FILTER(1, 0, 0, bits, 32, wordsize - bits)
>  
>  static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
>  	[ID_AD7170] = {
> -		.channel = AD7780_CHANNEL(12, 24),
> +		.channel = AD7170_CHANNEL(12, 24),
>  		.pattern = AD7170_PATTERN,
>  		.pattern_mask = AD7170_PATTERN_MASK,
>  		.is_ad778x = false,
>  	},
>  	[ID_AD7171] = {
> -		.channel = AD7780_CHANNEL(16, 24),
> +		.channel = AD7170_CHANNEL(16, 24),
>  		.pattern = AD7170_PATTERN,
>  		.pattern_mask = AD7170_PATTERN_MASK,
>  		.is_ad778x = false,
> @@ -173,6 +230,7 @@ static const struct ad7780_chip_info
> ad7780_chip_info_tbl[] = {
>  
>  static const struct iio_info ad7780_info = {
>  	.read_raw = ad7780_read_raw,
> +	.write_raw = ad7780_write_raw,
>  };
>  
>  static int ad7780_probe(struct spi_device *spi)
> @@ -222,6 +280,18 @@ static int ad7780_probe(struct spi_device *spi)
>  		goto error_disable_reg;
>  	}
>  
> +	if (st->chip_info->is_ad778x) {
> +		st->gain_gpio = devm_gpiod_get_optional(&spi->dev,
> +							"gain",
> +							GPIOD_OUT_HIGH);
> +		if (IS_ERR(st->gain_gpio)) {

if the GPIO is optional, then we should continue in case of -ENODEV.

Shouldn't we have a devm_gpiod_get_optional() call also for filter_gpio?

> +			ret = PTR_ERR(st->gain_gpio);
> +			dev_err(&spi->dev, "Failed to request gain GPIO:
> %d\n",
> +				ret);
> +			goto error_disable_reg;
> +		}
> +	}
> +
>  	ret = ad_sd_setup_buffer_and_trigger(indio_dev);
>  	if (ret)
>  		goto error_disable_reg;
> diff --git a/include/linux/iio/adc/ad_sigma_delta.h
> b/include/linux/iio/adc/ad_sigma_delta.h
> index 730ead1a46df..6cadab6fd5fd 100644
> --- a/include/linux/iio/adc/ad_sigma_delta.h
> +++ b/include/linux/iio/adc/ad_sigma_delta.h
> @@ -173,6 +173,11 @@ int ad_sd_validate_trigger(struct iio_dev
> *indio_dev, struct iio_trigger *trig);
>  	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
>  		_storagebits, _shift, NULL, IIO_VOLTAGE, 0)
>  
> +#define AD_SD_CHANNEL_GAIN_FILTER(_si, _channel, _address, _bits, \
> +	_storagebits, _shift) \
> +	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> +		_storagebits, _shift, NULL, IIO_VOLTAGE,
> BIT(IIO_CHAN_INFO_RAW))
> +
>  #define AD_SD_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
>  	__AD_SD_CHANNEL(_si, 0, -1, _address, _bits, \
>  		_storagebits, _shift, NULL, IIO_TEMP, \