On Sat, 11 Jan 2025 20:22:36 -0300 Jonathan Santos <jonath4nns@xxxxxxxxx> wrote: > On 01/07, David Lechner wrote: > > On 1/7/25 9:24 AM, Jonathan Santos wrote: > > > Add ABI documentation specific to the ad7768-1 device, detailing > > > the decimation_rate attribute for better clarity and usability. > > > > > > Signed-off-by: Jonathan Santos <Jonathan.Santos@xxxxxxxxxx> > > > --- > > > .../ABI/testing/sysfs-bus-iio-adc-ad7768-1 | 13 +++++++++++++ > > > 1 file changed, 13 insertions(+) > > > create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-adc-ad7768-1 > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7768-1 b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7768-1 > > > new file mode 100644 > > > index 000000000000..065247f07cfb > > > --- /dev/null > > > +++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7768-1 > > > @@ -0,0 +1,13 @@ > > > +What: /sys/bus/iio/devices/iio:deviceX/decimation_rate_available > > > +KernelVersion: > > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > > +Description: > > > + Reading returns a range of possible decimation rate values. > > > + > > > +What: /sys/bus/iio/devices/iio:deviceX/decimation_rate > > > +KernelVersion: > > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > > +Description: > > > + Sets up the decimation rate for the digital filter. This can > > > + directly impact in the final sampling frequency. Reading returns > > > + the decimation rate. Writing sets the decimation rate. > > > > If this only affects the filter, I would suggest to add `filter_` to the > > beginning of the attribute names. > > > > Also, an explanation of how to interpret the numbers would be helpful. It looks > > like a unitless number that acts a sort of a multiplier or divider, but that > > part isn't so clear to me. > > > > Or... > > > > Since the decimation rate affects the -3dB point of the filters we could use > > the standard IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY instead of introducing > > a new attribute. > > Well, here the -3dB cutoff depends on the ODR, which is determined by both the MCLK > divider and decimation rate. > > Wideband: -3dB at 0.433 × ODR > Sinc5: -3dB at 0.204 × ODR > Sinc3: -3dB at 0.2617 × ODR > > If we use _filter_low_pass_3db_frequency to control the decimation and _sampling_frequency > to control the MCLK divider, wouldn’t it be confusing for one to always affect the other? > A different ODR would result in a different cutoff, and vice versa. We should definitely not have a filter control changing sampling frequency (which tends to be a more common control for users to fiddle with). However the other way around is fine. So for a given _sampling_frequency present via in_xx_filter_low_pass_3db_frequency_available the list of possible 3db frequencies and use them to configure the decimation. > > Would something like <type>[_name]_oversampling_ratio make more sense? Let me know what you think I'd rather not if we can avoid that new ABI, but it is is better than a new term like decimation_rate. Jonathan >
