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>

diff --git a/drivers/staging/iio/adc/ad7793.c b/drivers/staging/iio/adc/ad7793.c
index 56014a8b687676fb7c1063cb879ac1840bf78f39..3c8d1d4c6192c1d1c0f1fe3d2a0e899372e2ad1f 100644 (file)
--- 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;