diff options
| author | Marcus Folkesson <marcus.folkesson@gmail.com> | 2022-07-22 15:07:20 +0200 |
|---|---|---|
| committer | Jonathan Cameron <Jonathan.Cameron@huawei.com> | 2022-08-21 18:24:16 +0100 |
| commit | 9e2238e3ae40d371a1130226e0e740aa1601efa6 (patch) | |
| tree | 45a66365f957cb1451c3ddc28f828db82f2fbe47 /drivers/iio | |
| parent | cfbd76d5c9c449739bb74288d982bccf9ff822f4 (diff) | |
iio: adc: mcp3911: use correct formula for AD conversion
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@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220722130726.7627-4-marcus.folkesson@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Diffstat (limited to 'drivers/iio')
| -rw-r--r-- | drivers/iio/adc/mcp3911.c | 17 |
1 files 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; } |