iio: adc: meson-saradc: add calibration

This patch adds calibration for the Meson SAR ADC.
Points 25% vref and 75% vref are used for calibration.
It uses a simple linear calibration function: SCALE * val + BIAS

Successfully tested on a Odroid C2.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
index cde9ca7a01b88bdb408e2cf6e023fc566766e4d9..dd4190b50df6a71a43d0fb22175ddb3f1e7d64c7 100644 (file)
--- 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
 
 #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);