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

[Jonathan Cameron <jic23-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On 31/10/16 08:48, Rama Krishna Phani A wrote:
> Hi Jonathan,
> 
> On 30-Oct-16 11:05 PM, Jonathan Cameron wrote:
>> 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?
> There are several channels in the ADC of PMIC which can be used to
> measure voltage, temperature, current etc., Hardware provides
> readings for all channels in adc code. That adc code needs to be
> converted to voltage. The logic for conversion of adc code to voltage
> is common for all ADC channels(voltage, temperature and current
> .,etc). Once voltage is obtained ., scaling is done on that voltage.
> 
> For Ex., Thermal SW wants to know the temperature of thermistor on
> PMIC and it expects the temperature to be reported in millidegC. ADC
> channel is used to read the adc code and convert it to voltage. Once
> the voltage is available based on the thermistor spec that voltage is
> mapped to a temperature and then that value is reported to Thermal
> SW.
> 
> Mapping of voltage to temperature is called scaling for that channel
> and scaling function can be different per channel based on how the
> voltage is reported.
Is the thermistor always part of the device? (i.e. in the chip) in which
case this might be fine.  If it's external then it needs to be described
by a separate device which acts as a consumer of the IIO channel and
in turn provides the scaled output to thermal.

The thermistor should really be separately described.   This is already
done in drivers/hwmon/ntc_thermistor 

Are any of these scalings characteristics of the chip supported by
this driver, or are they the result of external hardware?
>>
>> 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?
>>
> When a true raw read is requested .,Scaling is not applied.
>> There are several unconnected looking changes in here...
>>>
>>> Signed-off-by: Rama Krishna Phani A <rphani-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.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'.
> Yes., its raw value.
>>> -    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...
>>
> With the help of IIO sysfs ., we can read the ADC channel readings
> either in RAW format or in processed format. There are two separate
> individual entries to read the ADC channel either in Raw format or in
> processed format. Most of the clients for ADC expect the readings in
> processed format.
If we are talking in kernel, that is worked out by the application of
scale.  The IIO in kernel interfaces will do this automatically.

I we are talking in userspace, then the userspace needs to be
extended to support raw and scale reading.
>> 

>>>  /*
>>> @@ -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?
> We can choose how we want to display our adc channel entries in sysfs. Am using the child node name to be displayed as the sysfs entry rather than channel number for easy interpretation.
> 
> For ex: for vcoin(coin battery voltage channel.,) with this change it appears like below in iio adc sysfs
> 
> "in_voltage_vcoin_input"
No.  This introduces a mass of undocumented (and uncontrolled) ABI.
If there are reasons to add such a label then it should not be done
in the file name.
> 
>>>          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...
> reason explained above.
>>>          iio_chan->address = index++;
>>>
>>>          iio_chan++;
>>>
>>
> 
> Thanks,
> Ramakrishna
> 
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