From: Marcus Folkesson marcus.folkesson@gmail.com
commit 9e2238e3ae40d371a1130226e0e740aa1601efa6 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iio/adc/mcp3911.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
--- 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_d
*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; }