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

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

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"
>
> 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>

> ---
> 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