iio: adc: meson-saradc: improve meson_sar_adc_read_raw_sample

After sampling there should always be only one value in the FIFO.
This also applies to averaging mode as the averaging is done
chip-internally. So we don't have to loop and let the driver
complain if there's not exactly one value in the FIFO.

If the value belongs to a different channel then don't silently
swallow the value but complain.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-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 9f186de..cde9ca7 100644 (file)
--- a/drivers/iio/adc/meson_saradc.c
+++ b/drivers/iio/adc/meson_saradc.c
@@ -278,33 +278,31 @@ static int meson_sar_adc_read_raw_sample(struct iio_dev *indio_dev,
                                         int *val)
 {
        struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
-       int regval, fifo_chan, fifo_val, sum = 0, count = 0;
+       int regval, fifo_chan, fifo_val, count;
 
        if(!wait_for_completion_timeout(&priv->done,
                                msecs_to_jiffies(MESON_SAR_ADC_TIMEOUT)))
                return -ETIMEDOUT;
 
-       while (meson_sar_adc_get_fifo_count(indio_dev) > 0 &&
-              count < MESON_SAR_ADC_MAX_FIFO_SIZE) {
-               regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, &regval);
-
-               fifo_chan = FIELD_GET(MESON_SAR_ADC_FIFO_RD_CHAN_ID_MASK,
-                                     regval);
-               if (fifo_chan != chan->channel)
-                       continue;
-
-               fifo_val = FIELD_GET(MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK,
-                                    regval);
-               fifo_val &= (BIT(priv->data->resolution) - 1);
-
-               sum += fifo_val;
-               count++;
+       count = meson_sar_adc_get_fifo_count(indio_dev);
+       if (count != 1) {
+               dev_err(&indio_dev->dev,
+                       "ADC FIFO has %d element(s) instead of one\n", count);
+               return -EINVAL;
        }
 
-       if (!count)
-               return -ENOENT;
+       regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, &regval);
+       fifo_chan = FIELD_GET(MESON_SAR_ADC_FIFO_RD_CHAN_ID_MASK, regval);
+       if (fifo_chan != chan->channel) {
+               dev_err(&indio_dev->dev,
+                       "ADC FIFO entry belongs to channel %d instead of %d\n",
+                       fifo_chan, chan->channel);
+               return -EINVAL;
+       }
 
-       *val = sum / count;
+       fifo_val = FIELD_GET(MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK, regval);
+       fifo_val &= GENMASK(priv->data->resolution - 1, 0);
+       *val = fifo_val;
 
        return 0;
 }