[PATCH 5.4 40/69] iio: mtk-auxadc: fix case IIO_CHAN_INFO_PROCESSED

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Hui Liu <hui.liu@mediatek.com>

commit c2980c64c7fd4585d684574c92d1624d44961edd upstream.

The previous driver does't apply the necessary scaling to take the
voltage range into account.
We change readback value from raw data to input voltage to fix case
IIO_CHAN_INFO_PROCESSED.

Fixes: ace4cdfe67be ("iio: adc: mt2701: Add Mediatek auxadc driver for mt2701.")
Signed-off-by: Hui Liu <hui.liu@mediatek.com>
Link: https://lore.kernel.org/r/20210926073028.11045-2-hui.liu@mediatek.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/iio/adc/mt6577_auxadc.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/iio/adc/mt6577_auxadc.c
+++ b/drivers/iio/adc/mt6577_auxadc.c
@@ -82,6 +82,10 @@ static const struct iio_chan_spec mt6577
 	MT6577_AUXADC_CHANNEL(15),
 };
 
+/* For Voltage calculation */
+#define VOLTAGE_FULL_RANGE  1500	/* VA voltage */
+#define AUXADC_PRECISE      4096	/* 12 bits */
+
 static int mt_auxadc_get_cali_data(int rawdata, bool enable_cali)
 {
 	return rawdata;
@@ -191,6 +195,10 @@ static int mt6577_auxadc_read_raw(struct
 		}
 		if (adc_dev->dev_comp->sample_data_cali)
 			*val = mt_auxadc_get_cali_data(*val, true);
+
+		/* Convert adc raw data to voltage: 0 - 1500 mV */
+		*val = *val * VOLTAGE_FULL_RANGE / AUXADC_PRECISE;
+
 		return IIO_VAL_INT;
 
 	default: