On Fri, 22 Jul 2022 15:07:20 +0200
Marcus Folkesson <marcus.folkesson@xxxxxxxxx> wrote:
> 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>
Patches 1-3 now applied to the fixes-togreg branch of iio.git
which is currently based on char-misc-linus which is at
Linus' tree just after he took the char-misc pull requests for
the merge window. I might rebase this on rc1 once available
or I might just use the base as is. Either way, it should be
fine in linux-next
Thanks,
Jonathan
> ---
> 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;
> }
>
