Re: [PATCH v3] iio: adc: meson-saradc: add calibration

[Jonathan Cameron <jic23@kernel.org>]

On 24/03/17 22:24, Martin Blumenstingl wrote:
> Hi Heiner,
> 
> On Sat, Mar 18, 2017 at 7:38 PM, Heiner Kallweit <hkallweit1@gmail.com> wrote:
>> This patch adds calibration for the Meson SAR ADC.
>> Points 25% vref and 75% vref are used for calibration.
>> It usesa simple linear calibration function: SCALE * val + BIAS
> nit: should be "It uses a"
Fixed whilst applying.
>>
>> Successfully tested on a Odroid C2.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> looks good to me, so:
> 
> Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan
> 
>> ---
>> v2:
>> - added calibration scale
>> v3:
>> - added define MILLION
>> - don't bail out if calibration fails
>> ---
>>  drivers/iio/adc/meson_saradc.c | 77 ++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 75 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
>> index cde9ca7a..dd4190b5 100644
>> --- a/drivers/iio/adc/meson_saradc.c
>> +++ b/drivers/iio/adc/meson_saradc.c
>> @@ -166,6 +166,8 @@
>>
>>  #define MESON_SAR_ADC_MAX_FIFO_SIZE                            32
>>  #define MESON_SAR_ADC_TIMEOUT                                  100 /* ms */
>> +/* for use with IIO_VAL_INT_PLUS_MICRO */
>> +#define MILLION                                                        1000000
> back when the initial driver was reviewed I was asked to prefix all
> defines (so they won't clash with defines from other drivers, see [0])
> - this is why all defines start with MESON_SAR_ADC_
> if Jonathan or Peter think that it's worth renaming this #define then
> you could rename it to MESON_SAR_ADC_CALIBSCALE_REF (that's what I
> came up with, feel free to choose any other/more suitable name though)
> 
>>  #define MESON_SAR_ADC_CHAN(_chan) {                                    \
>>         .type = IIO_VOLTAGE,                                            \
>> @@ -173,7 +175,9 @@
>>         .channel = _chan,                                               \
>>         .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |                  \
>>                                 BIT(IIO_CHAN_INFO_AVERAGE_RAW),         \
>> -       .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),           \
>> +       .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |          \
>> +                               BIT(IIO_CHAN_INFO_CALIBBIAS) |          \
>> +                               BIT(IIO_CHAN_INFO_CALIBSCALE),          \
>>         .datasheet_name = "SAR_ADC_CH"#_chan,                           \
>>  }
>>
>> @@ -233,6 +237,8 @@ struct meson_sar_adc_priv {
>>         struct clk                              *adc_div_clk;
>>         struct clk_divider                      clk_div;
>>         struct completion                       done;
>> +       int                                     calibbias;
>> +       int                                     calibscale;
>>  };
>>
>>  static const struct regmap_config meson_sar_adc_regmap_config = {
>> @@ -252,6 +258,17 @@ static unsigned int meson_sar_adc_get_fifo_count(struct iio_dev *indio_dev)
>>         return FIELD_GET(MESON_SAR_ADC_REG0_FIFO_COUNT_MASK, regval);
>>  }
>>
>> +static int meson_sar_adc_calib_val(struct iio_dev *indio_dev, int val)
>> +{
>> +       struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
>> +       int tmp;
>> +
>> +       /* use val_calib = scale * val_raw + offset calibration function */
>> +       tmp = div_s64((s64)val * priv->calibscale, MILLION) + priv->calibbias;
>> +
>> +       return clamp(tmp, 0, (1 << priv->data->resolution) - 1);
>> +}
>> +
>>  static int meson_sar_adc_wait_busy_clear(struct iio_dev *indio_dev)
>>  {
>>         struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
>> @@ -302,7 +319,7 @@ static int meson_sar_adc_read_raw_sample(struct iio_dev *indio_dev,
>>
>>         fifo_val = FIELD_GET(MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK, regval);
>>         fifo_val &= GENMASK(priv->data->resolution - 1, 0);
>> -       *val = fifo_val;
>> +       *val = meson_sar_adc_calib_val(indio_dev, fifo_val);
>>
>>         return 0;
>>  }
>> @@ -527,6 +544,15 @@ static int meson_sar_adc_iio_info_read_raw(struct iio_dev *indio_dev,
>>                 *val2 = priv->data->resolution;
>>                 return IIO_VAL_FRACTIONAL_LOG2;
>>
>> +       case IIO_CHAN_INFO_CALIBBIAS:
>> +               *val = priv->calibbias;
>> +               return IIO_VAL_INT;
>> +
>> +       case IIO_CHAN_INFO_CALIBSCALE:
>> +               *val = priv->calibscale / MILLION;
>> +               *val2 = priv->calibscale % MILLION;
>> +               return IIO_VAL_INT_PLUS_MICRO;
>> +
>>         default:
>>                 return -EINVAL;
>>         }
>> @@ -762,6 +788,47 @@ static irqreturn_t meson_sar_adc_irq(int irq, void *data)
>>         return IRQ_HANDLED;
>>  }
>>
>> +static int meson_sar_adc_calib(struct iio_dev *indio_dev)
>> +{
>> +       struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
>> +       int ret, nominal0, nominal1, value0, value1;
>> +
>> +       /* use points 25% and 75% for calibration */
>> +       nominal0 = (1 << priv->data->resolution) / 4;
>> +       nominal1 = (1 << priv->data->resolution) * 3 / 4;
>> +
>> +       meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_VDD_DIV4);
>> +       usleep_range(10, 20);
>> +       ret = meson_sar_adc_get_sample(indio_dev,
>> +                                      &meson_sar_adc_iio_channels[7],
>> +                                      MEAN_AVERAGING, EIGHT_SAMPLES, &value0);
>> +       if (ret < 0)
>> +               goto out;
>> +
>> +       meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_VDD_MUL3_DIV4);
>> +       usleep_range(10, 20);
>> +       ret = meson_sar_adc_get_sample(indio_dev,
>> +                                      &meson_sar_adc_iio_channels[7],
>> +                                      MEAN_AVERAGING, EIGHT_SAMPLES, &value1);
>> +       if (ret < 0)
>> +               goto out;
>> +
>> +       if (value1 <= value0) {
>> +               ret = -EINVAL;
>> +               goto out;
>> +       }
>> +
>> +       priv->calibscale = div_s64((nominal1 - nominal0) * (s64)MILLION,
>> +                                  value1 - value0);
>> +       priv->calibbias = nominal0 - div_s64((s64)value0 * priv->calibscale,
>> +                                            MILLION);
>> +       ret = 0;
>> +out:
>> +       meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_CH7_INPUT);
>> +
>> +       return ret;
>> +}
>> +
>>  static const struct iio_info meson_sar_adc_iio_info = {
>>         .read_raw = meson_sar_adc_iio_info_read_raw,
>>         .driver_module = THIS_MODULE,
>> @@ -901,6 +968,8 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
>>                 return PTR_ERR(priv->vref);
>>         }
>>
>> +       priv->calibscale = MILLION;
>> +
>>         ret = meson_sar_adc_init(indio_dev);
>>         if (ret)
>>                 goto err;
>> @@ -909,6 +978,10 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
>>         if (ret)
>>                 goto err;
>>
>> +       ret = meson_sar_adc_calib(indio_dev);
>> +       if (ret)
>> +               dev_warn(&pdev->dev, "calibration failed\n");
>> +
>>         platform_set_drvdata(pdev, indio_dev);
>>
>>         ret = iio_device_register(indio_dev);
>> --
>> 2.12.0
>>
>>
> 
> Regards,
> Martin
> 
> [0] http://lists.infradead.org/pipermail/linux-amlogic/2017-January/002009.html
>