iio: adc: stm32-dfsdm: add id registers support

Add support of identification registers to STM32 DFSDM
to allow hardware capabilities discovery and configuration check.
The number of filters and channels, are read from registers,
when they are available.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Link: https://lore.kernel.org/r/20230105125331.328275-1-olivier.moysan@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

ASoC: stm32: dfsdm: add actual resolution trace

Add a trace to report actual resolution of audio samples.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Link: https://lore.kernel.org/r/20201007153459.22155-3-olivier.moysan@st.com
Signed-off-by: Mark Brown <broonie@kernel.org>

iio: adc: stm32-dfsdm: add fast mode support

The use of fast mode allows to get a larger set of solution
for filter parameters. This can be useful to reach a better
output sample resolution, when fast mode can be used.

Fast mode is selected at startup if it is relevant.
The startup is performed in postenable callback context,
where there are too tight time constraints for filter parameters
computation. For this reason both fast and non fast filter parameters
are pre-computed previously.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: stm32-dfsdm: fix output resolution

In buffered mode, output samples are shifted left
unconditionally. This works for filter order 3,
but this shift is not adapted for other filter orders.
Compute required shift, left or right, and shift
output data accordingly.
Add also saturation management to avoid wrap-around
when maximum positive sample is reached.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Fixes: eca949800d2d ("IIO: ADC: add stm32 DFSDM support for PDM microphone")
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

IIO: ADC: add stm32 DFSDM core support

Add driver for stm32 DFSDM pheripheral. Its converts a sigma delta
stream in n bit samples through a low pass filter and an integrator.
stm32-dfsdm-core driver is the core part supporting the filter
instances dedicated to sigma-delta ADC or audio PDM microphone purpose.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>