The ADC conversion is actually not rail-to-rail but with a factor 1.5.
Make use of this factor when calculating actual voltage.
Fixes: 3a89b289df5d ("iio: adc: add support for mcp3911")
Signed-off-by: Marcus Folkesson <marcus.folkesson@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
---
drivers/iio/adc/mcp3911.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
index f8875076ae80..890af7dca62d 100644
--- a/drivers/iio/adc/mcp3911.c
+++ b/drivers/iio/adc/mcp3911.c
@@ -40,8 +40,8 @@
#define MCP3911_CHANNEL(x) (MCP3911_REG_CHANNEL0 + x * 3)
#define MCP3911_OFFCAL(x) (MCP3911_REG_OFFCAL_CH0 + x * 6)
-/* Internal voltage reference in uV */
-#define MCP3911_INT_VREF_UV 1200000
+/* Internal voltage reference in mV */
+#define MCP3911_INT_VREF_MV 1200
#define MCP3911_REG_READ(reg, id) ((((reg) << 1) | ((id) << 5) | (1 << 0)) & 0xff)
#define MCP3911_REG_WRITE(reg, id) ((((reg) << 1) | ((id) << 5) | (0 << 0)) & 0xff)
@@ -139,11 +139,18 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
*val = ret / 1000;
} else {
- *val = MCP3911_INT_VREF_UV;
+ *val = MCP3911_INT_VREF_MV;
}
- *val2 = 24;
- ret = IIO_VAL_FRACTIONAL_LOG2;
+ /*
+ * For 24bit Conversion
+ * Raw = ((Voltage)/(Vref) * 2^23 * Gain * 1.5
+ * Voltage = Raw * (Vref)/(2^23 * Gain * 1.5)
+ */
+
+ /* val2 = (2^23 * 1.5) */
+ *val2 = 12582912;
+ ret = IIO_VAL_FRACTIONAL;
break;
}
--
2.37.1
