| Message ID | 20220722130726.7627-4-marcus.folkesson@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | Improve MCP3911 driver | expand |
On Fri, 22 Jul 2022 15:07:20 +0200 Marcus Folkesson <marcus.folkesson@gmail.com> 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@gmail.com> > Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com> 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; > } >
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; }
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> --- drivers/iio/adc/mcp3911.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)