linux-kernel - Re: [PATCH v2 0/3] Re-add filter_type/filter

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Message-ID: <e7e9266f-082a-4bb4-931c-505c7ff20d47@baylibre.com>
Date: Tue, 7 Jan 2025 11:48:25 -0600
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Marcelo Schmitt <marcelo.schmitt@...log.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, cosmin.tanislav@...log.com, jic23@...nel.org,
 lars@...afoo.de, granquet@...libre.com, u.kleine-koenig@...libre.com
Subject: Re: [PATCH v2 0/3] Re-add filter_type/filter_mode

On 1/7/25 11:44 AM, Marcelo Schmitt wrote:
> On 01/07, David Lechner wrote:
>> On 1/7/25 9:11 AM, Marcelo Schmitt wrote:
>>> Better document sysfs ABI for ADC digital filter configuration.
>>>
>>> Change log v1 -> v2
>>> - Split into 3 patches.
>>> - Re-added sysfs-bus-iio-adc-ad4130 to keep filter_mode separate from filter_type.
>>
>> If ad7779 is the only driver with filter_type{,available} attributes while
>> ad4130 and admv8818 both have filter_mode{,available} attributes, shouldn't we
>> be deprecating filter_type and promoting filter_mode?
> 
> Oh, I had only grepped the adc dir and I didn't noticed admv8818 also had
> filter_mode.
> Hmm, don't know, though still biased towards filter_type.
> 
> - The admv8818 filter_mode_available ABI exports different values (auto,
>   manual, bypass).

Ah, I didn't look that far, so yes, I agree this is a good reason to standardize
on filter_type instead.

> - AD7768-1, ADAQ7768-1, AD7768/AD7768-4, AD7124-4, and AD4170 datasheets
>   refer to sinc filters as filter types (though not all of those designs are
>   supported in IIO or have filter attributes).
> - The AD4130 datasheets also refers to the digital filter as filter type in
>   some occasions.
> 
> But some datasheets seem to use filter mode and filter type interchangeably
> so I don't know. The admv8818 use case is valid and is both low and high-pass
> filtering while the ADCs sinc digital filters act like low-pass filter.
> Maybe even provide a different name for ADC digital filtering?
> digital_filter_type (or digital_filter_mode)?.
> 
> Thanks for pointing that out.