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
Successfully tested on a Odroid C2.
Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Tested-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
---
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
#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
--
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