Re: [PATCH 2/4] staging:iio:dac:ad5791: Allow asymmetrical reference voltages

[Jonathan Cameron <jic23@cam.ac.uk>]

On 10/19/11 13:23, Lars-Peter Clausen wrote:
> The ad5791 currently assumes that the negative and positive supply have the
> same absolute value, which is not necessarily true. This patch introduces a
> offset attribute which will contain the negative supply voltage scaled
> according to the iio spec. The raw attribute now accepts values in the range
> of 0 to max instead of -max/2 to max/2.
> 
> While we are at it also fix the vref span calculation. Since both positive and
> negative reference voltages are specificed as absolute values we need to add
> them and not subtract them to get the reference voltage span.
Everything commented here is fine, but one odd looking removal...
> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> ---
>  drivers/staging/iio/dac/ad5791.c |   24 ++++++++++++++++--------
>  drivers/staging/iio/dac/ad5791.h |    2 ++
>  2 files changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/staging/iio/dac/ad5791.c b/drivers/staging/iio/dac/ad5791.c
> index 9a76c43..c465fcf 100644
> --- a/drivers/staging/iio/dac/ad5791.c
> +++ b/drivers/staging/iio/dac/ad5791.c
> @@ -77,7 +77,8 @@ static int ad5791_spi_read(struct spi_device *spi, u8 addr, u32 *val)
>  	.indexed = 1,					\
>  	.address = AD5791_ADDR_DAC0,			\
>  	.channel = 0,					\
> -	.info_mask = (1 << IIO_CHAN_INFO_SCALE_SHARED),	\
> +	.info_mask = (1 << IIO_CHAN_INFO_SCALE_SHARED) | \
> +		(1 << IIO_CHAN_INFO_OFFSET_SHARED),	\
>  	.scan_type = IIO_ST('u', bits, 24, shift)	\
>  }
>  
> @@ -225,6 +226,7 @@ static int ad5791_read_raw(struct iio_dev *indio_dev,
>  			   long m)
>  {
>  	struct ad5791_state *st = iio_priv(indio_dev);
> +	u64 val64;
>  	int ret;
>  
>  	switch (m) {
> @@ -234,12 +236,16 @@ static int ad5791_read_raw(struct iio_dev *indio_dev,
>  			return ret;
>  		*val &= AD5791_DAC_MASK;
>  		*val >>= chan->scan_type.shift;
> -		*val -= (1 << (chan->scan_type.realbits - 1));
>  		return IIO_VAL_INT;
>  	case (1 << IIO_CHAN_INFO_SCALE_SHARED):
>  		*val = 0;
>  		*val2 = (st->vref_mv * 1000) >> chan->scan_type.realbits;
>  		return IIO_VAL_INT_PLUS_MICRO;
> +	case (1 << IIO_CHAN_INFO_OFFSET_SHARED):
> +		val64 = (((u64)st->vref_neg_mv) << chan->scan_type.realbits);
> +		do_div(val64, st->vref_mv);
> +		*val = -val64;
> +		return IIO_VAL_INT;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -257,7 +263,6 @@ static int ad5791_write_raw(struct iio_dev *indio_dev,
>  
>  	switch (mask) {
>  	case 0:
> -		val += (1 << (chan->scan_type.realbits - 1));
This line looks suspicious.  What is it doing in this patch?
I'll be honest and say I'm not sure why it was there in the first place, but
I can't immediately see what it has to do with the rest of the patch.
>  		val &= AD5791_RES_MASK(chan->scan_type.realbits);
>  		val <<= chan->scan_type.shift;
>  
> @@ -309,12 +314,15 @@ static int __devinit ad5791_probe(struct spi_device *spi)
>  	st->pwr_down = true;
>  	st->spi = spi;
>  
> -	if (!IS_ERR(st->reg_vss) && !IS_ERR(st->reg_vdd))
> -		st->vref_mv = (pos_voltage_uv - neg_voltage_uv) / 1000;
> -	else if (pdata)
> -		st->vref_mv = pdata->vref_pos_mv - pdata->vref_neg_mv;
> -	else
> +	if (!IS_ERR(st->reg_vss) && !IS_ERR(st->reg_vdd)) {
> +		st->vref_mv = (pos_voltage_uv + neg_voltage_uv) / 1000;
> +		st->vref_neg_mv = neg_voltage_uv / 1000;
> +	} else if (pdata) {
> +		st->vref_mv = pdata->vref_pos_mv + pdata->vref_neg_mv;
> +		st->vref_neg_mv = pdata->vref_neg_mv;
> +	} else {
>  		dev_warn(&spi->dev, "reference voltage unspecified\n");
> +	}
>  
>  	ret = ad5791_spi_write(spi, AD5791_ADDR_SW_CTRL, AD5791_SWCTRL_RESET);
>  	if (ret)
> diff --git a/drivers/staging/iio/dac/ad5791.h b/drivers/staging/iio/dac/ad5791.h
> index 2a50a11..fd7edbd 100644
> --- a/drivers/staging/iio/dac/ad5791.h
> +++ b/drivers/staging/iio/dac/ad5791.h
> @@ -82,6 +82,7 @@ struct ad5791_chip_info {
>   * @reg_vss:		negative supply regulator
>   * @chip_info:		chip model specific constants
>   * @vref_mv:		actual reference voltage used
> + * @vref_neg_mv:	voltage of the negative supply
>   * @pwr_down_mode	current power down mode
>   */
>  
> @@ -91,6 +92,7 @@ struct ad5791_state {
>  	struct regulator		*reg_vss;
>  	const struct ad5791_chip_info	*chip_info;
>  	unsigned short			vref_mv;
> +	unsigned int			vref_neg_mv;
>  	unsigned			ctrl;
>  	unsigned			pwr_down_mode;
>  	bool				pwr_down;