staging:iio:ad7793: Fix temperature scale and offset

The temperature channel uses the internal 1.17V reference with 0.81 mv/C. The
reported temperature is in Kevlin, so we need to add the Kelvin to Celcius
offset when reporting the offset for the temperature channel.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

1 files changed, 18 insertions, 11 deletions

diff --git a/drivers/staging/iio/adc/ad7793.c b/drivers/staging/iio/adc/ad7793.c
index 56014a8b6876..3c8d1d4c6192 100644
--- a/drivers/staging/iio/adc/ad7793.c
+++ b/drivers/staging/iio/adc/ad7793.c
@@ -617,30 +617,37 @@ static int ad7793_read_raw(struct iio_dev *indio_dev,
                                 return IIO_VAL_INT_PLUS_NANO;
                         } else {
                                 /* 1170mV / 2^23 * 6 */
-                                scale_uv = (1170ULL * 100000000ULL * 6ULL)
-                                        >> (chan->scan_type.realbits -
-                                            (unipolar ? 0 : 1));
+                                scale_uv = (1170ULL * 100000000ULL * 6ULL);
                         }
                         break;
                 case IIO_TEMP:
-                        /* Always uses unity gain and internal ref */
-                        scale_uv = (2500ULL * 100000000ULL)
-                                >> (chan->scan_type.realbits -
-                                (unipolar ? 0 : 1));
+                                /* 1170mV / 0.81 mV/C / 2^23 */
+                                scale_uv = 1444444444444ULL;
                         break;
                 default:
                         return -EINVAL;
                 }
 
-                *val2 = do_div(scale_uv, 100000000) * 10;
-                *val =  scale_uv;
-
+                scale_uv >>= (chan->scan_type.realbits - (unipolar ? 0 : 1));
+                *val = 0;
+                *val2 = scale_uv;
                 return IIO_VAL_INT_PLUS_NANO;
         case IIO_CHAN_INFO_OFFSET:
                 if (!unipolar)
-                        *val -= (1 << (chan->scan_type.realbits - 1));
+                        *val = -(1 << (chan->scan_type.realbits - 1));
                 else
                         *val = 0;
+
+                /* Kelvin to Celsius */
+                if (chan->type == IIO_TEMP) {
+                        unsigned long long offset;
+                        unsigned int shift;
+
+                        shift = chan->scan_type.realbits - (unipolar ? 0 : 1);
+                        offset = 273ULL << shift;
+                        do_div(offset, 1444);
+                        *val -= offset;
+                }
                 return IIO_VAL_INT;
         }
         return -EINVAL;