Re: [PATCH V3 1/2] iio: adc: spmi-vadc: Update changes to support reporting of Raw adc code.

[Jonathan Cameron <jic23@kernel.org>]

On 26/10/16 15:41, Rama Krishna Phani A wrote:
> Logic to convert adc code to voltage is generic across all channels.
> Different scaling can be done on the obtained voltage to report in physical
> units. Implement separate function for generic conversion logic.
> Scaling functionality can be changed per channel. Update changes to support
> reporting of Raw adc code.
Pleas rewrite this description.  Perhaps give examples of the changes
it makes to what is read from the various attributes? 

I haven't immediately followed what this change is actually doing.

I 'think' the point here is to not apply the calibration to
the raw adc counts when a true raw read is requested?

There are several unconnected looking changes in here...
> 
> Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>
> ---
>  drivers/iio/adc/qcom-spmi-vadc.c | 54 +++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/iio/adc/qcom-spmi-vadc.c b/drivers/iio/adc/qcom-spmi-vadc.c
> index c2babe5..ff4d549 100644
> --- a/drivers/iio/adc/qcom-spmi-vadc.c
> +++ b/drivers/iio/adc/qcom-spmi-vadc.c
> @@ -1,5 +1,5 @@
>  /*
> - * Copyright (c) 2012-2014, The Linux Foundation. All rights reserved.
> + * Copyright (c) 2012-2016, The Linux Foundation. All rights reserved.
>   *
>   * This program is free software; you can redistribute it and/or modify
>   * it under the terms of the GNU General Public License version 2 and
> @@ -84,7 +84,7 @@
>  #define VADC_MAX_ADC_CODE			0xa800
>  
>  #define VADC_ABSOLUTE_RANGE_UV			625000
> -#define VADC_RATIOMETRIC_RANGE_UV		1800000
> +#define VADC_RATIOMETRIC_RANGE			1800
>  
>  #define VADC_DEF_PRESCALING			0 /* 1:1 */
>  #define VADC_DEF_DECIMATION			0 /* 512 */
> @@ -418,7 +418,7 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
>  	u16 read_1, read_2;
>  	int ret;
>  
> -	vadc->graph[VADC_CALIB_RATIOMETRIC].dx = VADC_RATIOMETRIC_RANGE_UV;
> +	vadc->graph[VADC_CALIB_RATIOMETRIC].dx = VADC_RATIOMETRIC_RANGE;
>  	vadc->graph[VADC_CALIB_ABSOLUTE].dx = VADC_ABSOLUTE_RANGE_UV;
>  
>  	prop = vadc_get_channel(vadc, VADC_REF_1250MV);
> @@ -468,21 +468,30 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
>  	return ret;
>  }
>  
> -static s32 vadc_calibrate(struct vadc_priv *vadc,
> -			  const struct vadc_channel_prop *prop, u16 adc_code)
> +static void vadc_scale_calib(struct vadc_priv *vadc, u16 adc_code,
> +			     const struct vadc_channel_prop *prop,
> +			     s64 *scale_voltage)
>  {
> -	const struct vadc_prescale_ratio *prescale;
> -	s64 voltage;
> +	*scale_voltage = (adc_code -
> +		vadc->graph[prop->calibration].gnd);
> +	*scale_voltage *= vadc->graph[prop->calibration].dx;
> +	*scale_voltage = div64_s64(*scale_voltage,
> +		vadc->graph[prop->calibration].dy);
> +	if (prop->calibration == VADC_CALIB_ABSOLUTE)
> +		*scale_voltage +=
> +		vadc->graph[prop->calibration].dx;
>  
> -	voltage = adc_code - vadc->graph[prop->calibration].gnd;
> -	voltage *= vadc->graph[prop->calibration].dx;
> -	voltage = div64_s64(voltage, vadc->graph[prop->calibration].dy);
> +	if (*scale_voltage < 0)
> +		*scale_voltage = 0;
> +}
>  
> -	if (prop->calibration == VADC_CALIB_ABSOLUTE)
> -		voltage += vadc->graph[prop->calibration].dx;
> +static s64 vadc_scale_fn(struct vadc_priv *vadc,
> +			 const struct vadc_channel_prop *prop, u16 adc_code)
> +{
> +	const struct vadc_prescale_ratio *prescale;
> +	s64 voltage = 0;
>  
> -	if (voltage < 0)
> -		voltage = 0;
> +	vadc_scale_calib(vadc, adc_code, prop, &voltage);
>  
>  	prescale = &vadc_prescale_ratios[prop->prescale];
>  
> @@ -552,11 +561,8 @@ static int vadc_read_raw(struct iio_dev *indio_dev,
>  		if (ret)
>  			break;
>  
> -		*val = vadc_calibrate(vadc, prop, adc_code);
> +		*val = vadc_scale_fn(vadc, prop, adc_code);
>  
> -		/* 2mV/K, return milli Celsius */
> -		*val /= 2;
> -		*val -= KELVINMIL_CELSIUSMIL;
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_RAW:
>  		prop = &vadc->chan_props[chan->address];
> @@ -564,12 +570,8 @@ static int vadc_read_raw(struct iio_dev *indio_dev,
>  		if (ret)
>  			break;
>  
> -		*val = vadc_calibrate(vadc, prop, adc_code);
> +		*val = (int)adc_code;
>  		return IIO_VAL_INT;
So this is 'more raw'.
> -	case IIO_CHAN_INFO_SCALE:
> -		*val = 0;
> -		*val2 = 1000;
> -		return IIO_VAL_INT_PLUS_MICRO;
>  	default:
>  		ret = -EINVAL;
>  		break;
> @@ -616,8 +618,8 @@ struct vadc_channels {
>  	VADC_CHAN(_dname, IIO_TEMP, BIT(IIO_CHAN_INFO_PROCESSED), _pre)	\
>  
>  #define VADC_CHAN_VOLT(_dname, _pre)					\
> -	VADC_CHAN(_dname, IIO_VOLTAGE,					\
> -		  BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),	\
> +	VADC_CHAN(_dname, IIO_VOLTAGE,				\
> +		  BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_PROCESSED),\
>  		  _pre)							\
It very unusual to report both raw and processed values.  Please explain
why that is needed here?  It may be valid to maintain backwards compatibility
of ABI. Which would be fine. However if I read the above correctly you are
changing what comes out of reading the raw value so the ABI just changed...


>  
>  /*
> @@ -850,9 +852,9 @@ static int vadc_get_dt_data(struct vadc_priv *vadc, struct device_node *node)
>  
>  		iio_chan->channel = prop.channel;
>  		iio_chan->datasheet_name = vadc_chan->datasheet_name;
> +		iio_chan->extend_name = child->name;
What's this change?
>  		iio_chan->info_mask_separate = vadc_chan->info_mask;
>  		iio_chan->type = vadc_chan->type;
> -		iio_chan->indexed = 1;
Or for that matter this one...
>  		iio_chan->address = index++;
>  
>  		iio_chan++;
>