Re: [PATCH v3 3/3] Documentation: ABI: IIO: Re-add sysfs-bus-iio-adc-ad4130

[David Lechner]

On 2/3/25 1:11 PM, Marcelo Schmitt wrote:
> The ad4130 driver exports in_voltageY-voltageZ_filter_mode and
> in_voltage-voltage_filter_mode_available attributes to user space. A
> previous patch merged the documentation for those attributes with the
> documentation for filter_type/filter_type_available into sysfs-bus-iio.
> Filter mode and filter type refer to the same feature which is the digital
> filter applied over ADC samples. However, since datasheets use the term
> `filter type` and ad4130 driver is the only one using filter_mode,
> deprecate the filter_mode ABI in favor of filter_type and keep the docs
> separate to avoid confusion and intricate attribute descriptions.
> 


> The digital filter helps shape the noise rejection bandwidth and is
> supposed to be adjusted according to the signal of interest. Depending on
> the particular ADC design, the digital filter configuration may have an
> impact on the output data rate (ODR) (which is equivalent to the sampling
> frequency for SAR ADCs - `sampling_frequency` ABI), 3dB cutoff frequency of
> the filter (`_low_pass_3db_frequency` attributes), or settling time.
> 
> Digital filters are a common feature among sigma-delta ADCs and
> IIO drivers set digital filters according to different attributes.
> ad4130 and ad7779 filter options are supported through dedicated
> filter_mode/filter_type attributes in sysfs.
> ad7768-1 and ad7173 set the sinc filters according to the
> sampling_frequency attribute. No filter_type attribute.
> ad7124 sets the digital filter according to a filter_low_pass_3db_frequency
> attribute so it doesn't export filter type attributes to user space.

These last two paragraphs seems a bit excessive and could be dropped.

> 
> Fixes: 01bb12922b60 ("Documentation: ABI: added filter mode doc in sysfs-bus-iio")
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
> ---
>  Documentation/ABI/testing/sysfs-bus-iio       |  1 -
>  .../ABI/testing/sysfs-bus-iio-adc-ad4130      | 20 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  3 files changed, 21 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
> index ff9cc09360dc..e4fd99c92d81 100644
> --- a/Documentation/ABI/testing/sysfs-bus-iio
> +++ b/Documentation/ABI/testing/sysfs-bus-iio
> @@ -2277,7 +2277,6 @@ Description:
>  		representing the sensor unique ID number.
>  
>  What:		/sys/bus/iio/devices/iio:deviceX/filter_type_available
> -What:		/sys/bus/iio/devices/iio:deviceX/in_voltage-voltage_filter_mode_available

Instead of removing the line, I think we need to replace it with:

/sys/bus/iio/devices/iio:deviceX/in_voltage-voltage_filter_type_available

(change mode to type)

This attribute is used in the previous patch.


>  KernelVersion:	6.1
>  Contact:	linux-iio@xxxxxxxxxxxxxxx
>  Description:
With those changes...

Reviewed-by: David Lechner <dlechner@xxxxxxxxxxxx>