[PATCH 3/3] iio:humidity:si7020: added processed data

[Nicola Corna <nicola@corna.info>]

The value given by the Si7013/20/21 modules needs a conversion using a
small expression in order to obtain the measurement in °C or %RH. This
patch adds the computation inside the si7020 module, allowing the user to
obtain the measurement in m°C and 10E-3%RH without any additional
calculation.

Signed-off-by: Nicola Corna <nicola@corna.info>
---
 drivers/iio/humidity/si7020.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
index a8bad04..c534706 100644
--- a/drivers/iio/humidity/si7020.c
+++ b/drivers/iio/humidity/si7020.c
@@ -70,6 +70,7 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+	case IIO_CHAN_INFO_PROCESSED:
 		if (holdmode) {
 			ret = i2c_smbus_read_word_data(*client,
 						       chan->type == IIO_TEMP ?
@@ -108,6 +109,17 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
 			else if (*val > 55575) /* 100%RH */
 				*val = 55575;
 		}
+		if (mask == IIO_CHAN_INFO_PROCESSED) {
+			/*
+			 * To avoid overflows the fractions can be simplified:
+			 * temperature --> 175720 / (65536 >> 2) = 21965 / 2048
+			 * humidity    --> 125000 / (65536 >> 2) = 15625 / 2048
+			 */
+			if (chan->type == IIO_TEMP)
+				*val = (*val - 4368) * 21965 / 2048;
+			else
+				*val = (*val - 768) * 15625 / 2048;
+		}
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		if (chan->type == IIO_TEMP)
@@ -142,12 +154,14 @@ static const struct iio_chan_spec si7020_channels[] = {
 	{
 		.type = IIO_HUMIDITYRELATIVE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |
+			BIT(IIO_CHAN_INFO_PROCESSED),
 	},
 	{
 		.type = IIO_TEMP,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |
+			BIT(IIO_CHAN_INFO_PROCESSED),
 	}
 };
 
-- 
2.5.0