On 01/12, Jonathan Cameron wrote: > On Sun, 12 Jan 2025 12:20:47 +0000 > Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > > 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. > Reading the code I realised I'd misunderstood this question. > Yes for controlling decimation via oversampling. Decimation (to me at least) > means 'ignoring' data but seems here it means averaging it. > Yes, for this device the decimation is indeed averaging the data. > Controls should be in order of preference > sampling_frequency (try to keep this constant as others chagnes - if you have to because of range issues, > tweak it) This is the rate we get data at after filter. > oversampling_ratio (again try to keep constant) - controls samples taken per output one. > _3db_frequency - anything left to control on the filter, or just a RO output of what it currently means. > > Jonathan > Great, then. Decimation will be controlled by oversampling, frequency modulator controlled by sampling frequency and _3db_frequency as RO attribute, since there are no parameters left. > > > > > > Jonathan > > > > > > > > > >
